Preface
Working with both Object-Oriented software and Relational Databases can be cumbersome and time-consuming.
Development costs are significantly higher due to a paradigm mismatch between how data is represented in objects versus relational databases.
Hibernate is an Object/Relational Mapping solution for Java environments.
The term Object/Relational Mapping refers to the technique of mapping data from an object model representation to a relational data model representation (and vice versa).
Hibernate not only takes care of the mapping from Java classes to database tables (and from Java data types to SQL data types), but also provides data query and retrieval facilities.
It can significantly reduce development time otherwise spent with manual data handling in SQL and JDBC.
Hibernate’s design goal is to relieve the developer from 95% of common data persistence-related programming tasks by eliminating the need for manual, hand-crafted data processing using SQL and JDBC.
However, unlike many other persistence solutions, Hibernate does not hide the power of SQL from you and guarantees that your investment in relational technology and knowledge is as valid as always.
Hibernate may not be the best solution for data-centric applications that only use stored-procedures to implement the business logic in the database, it is most useful with object-oriented domain models and business logic in the Java-based middle-tier.
However, Hibernate can certainly help you to remove or encapsulate vendor-specific SQL code and will help with the common task of result set translation from a tabular representation to a graph of objects.
System Requirements
Hibernate 6.3 requires at least Java 11 and JDBC 4.2.
Getting Started
While a strong background in SQL is not required to use Hibernate, a basic understanding of its concepts is useful — especially the principles of data modeling.
Understanding the basics of transactions and design patterns such as Unit of Work are important as well.
New users may want to first look at the tutorial-style Quick Start guide. This User Guide is really more of a reference guide. There is also a series of topical guides providing deep dives into various topics such as logging, compatibility and support, etc. |
Get Involved
-
Use Hibernate and report any bugs or issues you find. See Issue Tracker for details.
-
Try your hand at fixing some bugs or implementing enhancements. Again, see Issue Tracker.
-
Engage with the community using the methods listed in the Community section.
-
Help improve this documentation. Contact us on the developer mailing list or Zulip if you have interest.
-
Spread the word. Let the rest of your organization know about the benefits of Hibernate.
1. Architecture
1.1. Overview
Hibernate, as an ORM solution, effectively «sits between» the Java application data access layer and the Relational Database, as can be seen in the diagram above.
The Java application makes use of the Hibernate APIs to load, store, query, etc. its domain data.
Here we will introduce the essential Hibernate APIs.
This will be a brief introduction; we will discuss these contracts in detail later.
As a Jakarta Persistence provider, Hibernate implements the Java Persistence API specifications and the association between Jakarta Persistence interfaces and Hibernate specific implementations can be visualized in the following diagram:
- SessionFactory (
org.hibernate.SessionFactory
) -
A thread-safe (and immutable) representation of the mapping of the application domain model to a database.
Acts as a factory fororg.hibernate.Session
instances. TheEntityManagerFactory
is the Jakarta Persistence equivalent of aSessionFactory
and basically, those two converge into the sameSessionFactory
implementation.A
SessionFactory
is very expensive to create, so, for any given database, the application should have only one associatedSessionFactory
.
TheSessionFactory
maintains services that Hibernate uses across allSession(s)
such as second level caches, connection pools, transaction system integrations, etc. - Session (
org.hibernate.Session
) -
A single-threaded, short-lived object conceptually modeling a «Unit of Work» (PoEAA).
In Jakarta Persistence nomenclature, theSession
is represented by anEntityManager
.Behind the scenes, the Hibernate
Session
wraps a JDBCjava.sql.Connection
and acts as a factory fororg.hibernate.Transaction
instances.
It maintains a generally «repeatable read» persistence context (first level cache) of the application domain model. - Transaction (
org.hibernate.Transaction
) -
A single-threaded, short-lived object used by the application to demarcate individual physical transaction boundaries.
EntityTransaction
is the Jakarta Persistence equivalent and both act as an abstraction API to isolate the application from the underlying transaction system in use (JDBC or JTA).
2. Domain Model
The term domain model comes from the realm of data modeling.
It is the model that ultimately describes the problem domain you are working in.
Sometimes you will also hear the term persistent classes.
Ultimately the application domain model is the central character in an ORM.
They make up the classes you wish to map. Hibernate works best if these classes follow the Plain Old Java Object (POJO) / JavaBean programming model.
However, none of these rules are hard requirements.
Indeed, Hibernate assumes very little about the nature of your persistent objects. You can express a domain model in other ways (using trees of java.util.Map
instances, for example).
Historically applications using Hibernate would have used its proprietary XML mapping file format for this purpose.
With the coming of Jakarta Persistence, most of this information is now defined in a way that is portable across ORM/Jakarta Persistence providers using annotations (and/or standardized XML format).
This chapter will focus on Jakarta Persistence mapping where possible.
For Hibernate mapping features not supported by Jakarta Persistence we will prefer Hibernate extension annotations.
This chapter mostly uses «implicit naming» for table names, column names, etc. For details on |
2.1. Mapping types
Hibernate understands both the Java and JDBC representations of application data.
The ability to read/write this data from/to the database is the function of a Hibernate type.
A type, in this usage, is an implementation of the org.hibernate.type.Type
interface.
This Hibernate type also describes various behavioral aspects of the Java type such as how to check for equality, how to clone values, etc.
Usage of the word type The Hibernate type is neither a Java type nor a SQL data type. When you encounter the term type in discussions of Hibernate, it may refer to the Java type, the JDBC type, or the Hibernate type, depending on the context. |
To help understand the type categorizations, let’s look at a simple table and domain model that we wish to map.
Example 1. A simple table and domain model
create table Contact (
id integer not null,
first varchar(255),
last varchar(255),
middle varchar(255),
notes varchar(255),
starred boolean not null,
website varchar(255),
primary key (id)
)
@Entity(name = "Contact")
public static class Contact {
@Id
private Integer id;
private Name name;
private String notes;
private URL website;
private boolean starred;
//Getters and setters are omitted for brevity
}
@Embeddable
public class Name {
private String firstName;
private String middleName;
private String lastName;
// getters and setters omitted
}
In the broadest sense, Hibernate categorizes types into two groups:
-
Value types
-
Entity types
2.1.1. Value types
A value type is a piece of data that does not define its own lifecycle.
It is, in effect, owned by an entity, which defines its lifecycle.
Looked at another way, all the state of an entity is made up entirely of value types.
These state fields or JavaBean properties are termed persistent attributes.
The persistent attributes of the Contact
class are value types.
Value types are further classified into three sub-categories:
- Basic types
-
in mapping the
Contact
table, all attributes except for name would be basic types. Basic types are discussed in detail in Basic types - Embeddable types
-
the
name
attribute is an example of an embeddable type, which is discussed in details in Embeddable types - Collection types
-
although not featured in the aforementioned example, collection types are also a distinct category among value types. Collection types are further discussed in Collections
2.1.2. Entity types
Entities, by nature of their unique identifier, exist independently of other objects whereas values do not.
Entities are domain model classes which correlate to rows in a database table, using a unique identifier.
Because of the requirement for a unique identifier, entities exist independently and define their own lifecycle.
The Contact
class itself would be an example of an entity.
Mapping entities is discussed in detail in Entity types.
2.2. Basic values
A basic type is a mapping between a Java type and a single database column.
Hibernate can map many standard Java types (Integer
, String
, etc.) as basic
types. The mapping for many come from tables B-3 and B-4 in the JDBC specification[jdbc].
Others (URL
as VARCHAR
, e.g.) simply make sense.
Additionally, Hibernate provides multiple, flexible ways to indicate how the Java type
should be mapped to the database.
The Jakarta Persistence specification strictly limits the Java types that can be marked as basic to the following:
If provider portability is a concern, you should stick to just these basic types. Java Persistence 2.1 introduced the |
2.2.1. @Basic
Strictly speaking, a basic type is denoted by the jakarta.persistence.Basic
annotation.
Generally, the @Basic
annotation can be ignored as it is assumed by default. Both of the following
examples are ultimately the same.
Example 2. @Basic
explicit
@Entity(name = "Product")
public class Product {
@Id
@Basic
private Integer id;
@Basic
private String sku;
@Basic
private String name;
@Basic
private String description;
}
Example 3. @Basic
implied
@Entity(name = "Product")
public class Product {
@Id
private Integer id;
private String sku;
private String name;
private String description;
}
The @Basic
annotation defines 2 attributes.
optional
— boolean (defaults to true)-
Defines whether this attribute allows nulls. Jakarta Persistence defines
this as «a hint», which means the provider is free to ignore it. Jakarta Persistence also says that it will be
ignored if the type is primitive. As long as the type is not primitive, Hibernate will honor this
value. Works in conjunction with@Column#nullable
— see @Column. fetch
— FetchType (defaults to EAGER)-
Defines whether this attribute should be fetched eagerly or lazily.
EAGER
indicates that the value will be fetched as part of loading the owner.LAZY
values are
fetched only when the value is accessed. Jakarta Persistence requires providers to supportEAGER
, while support for
LAZY
is optional meaning that a provider is free to not support it. Hibernate supports lazy loading
of basic values as long as you are using its bytecode enhancement
support.
2.2.2. @Column
Jakarta Persistence defines rules for implicitly determining the name of tables and columns.
For a detailed discussion of implicit naming see Naming strategies.
For basic type attributes, the implicit naming rule is that the column name is the same as the attribute name.
If that implicit naming rule does not meet your requirements, you can explicitly tell Hibernate (and other providers) the column name to use.
Example 4. Explicit column naming
@Entity(name = "Product")
public class Product {
@Id
private Integer id;
private String sku;
private String name;
@Column(name = "NOTES")
private String description;
}
Here we use @Column
to explicitly map the description
attribute to the NOTES
column, as opposed to the
implicit column name description
. See Naming strategies for additional details.
The @Column
annotation defines other mapping information as well. See its Javadocs for details.
2.2.3. @Formula
@Formula
allows mapping any database computed value as a virtual read-only column.
|
Example 5. @Formula
mapping usage
@Entity(name = "Account")
public static class Account {
@Id
private Long id;
private Double credit;
private Double rate;
@Formula(value = "credit * rate")
private Double interest;
//Getters and setters omitted for brevity
}
When loading the Account
entity, Hibernate is going to calculate the interest
property using the configured @Formula
:
Example 6. Persisting an entity with a @Formula
mapping
doInJPA(this::entityManagerFactory, entityManager -> {
Account account = new Account();
account.setId(1L);
account.setCredit(5000d);
account.setRate(1.25 / 100);
entityManager.persist(account);
});
doInJPA(this::entityManagerFactory, entityManager -> {
Account account = entityManager.find(Account.class, 1L);
assertEquals(Double.valueOf(62.5d), account.getInterest());
});
INSERT INTO Account (credit, rate, id)
VALUES (5000.0, 0.0125, 1)
SELECT
a.id as id1_0_0_,
a.credit as credit2_0_0_,
a.rate as rate3_0_0_,
a.credit * a.rate as formula0_0_
FROM
Account a
WHERE
a.id = 1
The SQL fragment defined by the |
2.2.4. Mapping basic values
To deal with values of basic type, Hibernate needs to understand a few things about the mapping:
-
The capabilities of the Java type. For example:
-
How to compare values
-
How to calculate a hash-code
-
How to coerce values of this type to another type
-
-
The JDBC type it should use
-
How to bind values to JDBC statements
-
How to extract from JDBC results
-
-
Any conversion it should perform on the value to/from the database
-
The mutability of the value — whether the internal state can change like
java.util.Date
or is immutable likejava.lang.String
This section covers how Hibernate determines these pieces and how to influence that determination process.
The following sections focus on approaches introduced in version 6 to influence how Hibernate will This includes removal of the following deprecated legacy annotations:
See the 6.0 migration guide for discussions about migrating uses of these annotations The new annotations added as part of 6.0 support composing mappings in annotations |
Looking at this example, how does Hibernate know what mapping
to use for these attributes? The annotations do not really provide much information.
This is an illustration of Hibernate’s implicit basic-type resolution, which is a series of checks to determine
the appropriate mapping to use. Describing the complete process for implicit resolution is beyond the scope
of this documentation[2].
This is primarily driven by the Java type defined for the basic type, which can generally
be determined through reflection. Is the Java type an enum? Is it temporal? These answers
can indicate certain mappings be used.
The fallback is to map the value to the «recommended» JDBC type.
Worst case, if the Java type is Serializable
Hibernate will try to handle it via binary serialization.
For cases where the Java type is not a standard type or if some specialized handling is desired, Hibernate
provides 2 main approaches to influence this mapping resolution:
-
A compositional approach using a combination of one-or-more annotations to describe specific
aspects of the mapping. This approach is covered in Compositional basic mapping. -
The
UserType
contract, which is covered in Custom type mapping
These 2 approaches should be considered mutually exclusive. A custom UserType will always
take precedence over compositional annotations.
The next few sections look at common, standard Java types and discusses various ways to map them.
See Case Study : BitSet for examples of mapping BitSet
as a basic type using all of these approaches.
2.2.5. Enums
Hibernate supports the mapping of Java enums as basic value types in a number of different ways.
@Enumerated
The original Jakarta Persistence-compliant way to map enums was via the @Enumerated
or @MapKeyEnumerated
annotations, working on the principle that the enum values are stored according to one of 2 strategies indicated
by jakarta.persistence.EnumType
:
ORDINAL
-
stored according to the enum value’s ordinal position within the enum class, as indicated by
java.lang.Enum#ordinal
STRING
-
stored according to the enum value’s name, as indicated by
java.lang.Enum#name
Assuming the following enumeration:
Example 7. PhoneType
enumeration
public enum PhoneType {
LAND_LINE,
MOBILE;
}
In the ORDINAL example, the phone_type
column is defined as a (nullable) INTEGER type and would hold:
NULL
-
For null values
0
-
For the
LAND_LINE
enum 1
-
For the
MOBILE
enum
Example 8. @Enumerated(ORDINAL)
example
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
@Column(name = "phone_number")
private String number;
@Enumerated(EnumType.ORDINAL)
@Column(name = "phone_type")
private PhoneType type;
//Getters and setters are omitted for brevity
}
When persisting this entity, Hibernate generates the following SQL statement:
Example 9. Persisting an entity with an @Enumerated(ORDINAL)
mapping
Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("123-456-78990");
phone.setType(PhoneType.MOBILE);
entityManager.persist(phone);
INSERT INTO Phone (phone_number, phone_type, id)
VALUES ('123-456-78990', 1, 1)
In the STRING example, the phone_type
column is defined as a (nullable) VARCHAR type and would hold:
NULL
-
For null values
LAND_LINE
-
For the
LAND_LINE
enum MOBILE
-
For the
MOBILE
enum
Example 10. @Enumerated(STRING)
example
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
@Column(name = "phone_number")
private String number;
@Enumerated(EnumType.STRING)
@Column(name = "phone_type")
private PhoneType type;
//Getters and setters are omitted for brevity
}
Persisting the same entity as in the @Enumerated(ORDINAL)
example, Hibernate generates the following SQL statement:
Example 11. Persisting an entity with an @Enumerated(STRING)
mapping
INSERT INTO Phone (phone_number, phone_type, id)
VALUES ('123-456-78990', 'MOBILE', 1)
Using AttributeConverter
Let’s consider the following Gender
enum which stores its values using the 'M'
and 'F'
codes.
Example 12. Enum with a custom constructor
public enum Gender {
MALE('M'),
FEMALE('F');
private final char code;
Gender(char code) {
this.code = code;
}
public static Gender fromCode(char code) {
if (code == 'M' || code == 'm') {
return MALE;
}
if (code == 'F' || code == 'f') {
return FEMALE;
}
throw new UnsupportedOperationException(
"The code " + code + " is not supported!"
);
}
public char getCode() {
return code;
}
}
You can map enums in a Jakarta Persistence compliant way using a Jakarta Persistence AttributeConverter.
Example 13. Enum mapping with AttributeConverter
example
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
@Convert(converter = GenderConverter.class)
public Gender gender;
//Getters and setters are omitted for brevity
}
@Converter
public static class GenderConverter
implements AttributeConverter<Gender, Character> {
public Character convertToDatabaseColumn(Gender value) {
if (value == null) {
return null;
}
return value.getCode();
}
public Gender convertToEntityAttribute(Character value) {
if (value == null) {
return null;
}
return Gender.fromCode(value);
}
}
Here, the gender column is defined as a CHAR type and would hold:
NULL
-
For null values
'M'
-
For the
MALE
enum 'F'
-
For the
FEMALE
enum
For additional details on using AttributeConverters, see AttributeConverters section.
Jakarta Persistence explicitly disallows the use of an So, when using the |
Custom type
You can also map enums using a Hibernate custom type mapping.
Let’s again revisit the Gender enum example, this time using a custom Type to store the more standardized 'M'
and 'F'
codes.
Example 14. Enum mapping with custom Type example
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
@Type(GenderType.class)
@Column(length = 6)
public Gender gender;
//Getters and setters are omitted for brevity
}
public class GenderType extends UserTypeSupport<Gender> {
public GenderType() {
super(Gender.class, Types.CHAR);
}
}
public class GenderJavaType extends AbstractClassJavaType<Gender> {
public static final GenderJavaType INSTANCE =
new GenderJavaType();
protected GenderJavaType() {
super(Gender.class);
}
public String toString(Gender value) {
return value == null ? null : value.name();
}
public Gender fromString(CharSequence string) {
return string == null ? null : Gender.valueOf(string.toString());
}
public <X> X unwrap(Gender value, Class<X> type, WrapperOptions options) {
return CharacterJavaType.INSTANCE.unwrap(
value == null ? null : value.getCode(),
type,
options
);
}
public <X> Gender wrap(X value, WrapperOptions options) {
return Gender.fromCode(
CharacterJavaType.INSTANCE.wrap( value, options)
);
}
}
Again, the gender column is defined as a CHAR type and would hold:
NULL
-
For null values
'M'
-
For the
MALE
enum 'F'
-
For the
FEMALE
enum
For additional details on using custom types, see Custom type mapping section.
2.2.6. Boolean
By default, Boolean
attributes map to BOOLEAN
columns, at least when the database has a
dedicated BOOLEAN
type. On databases which don’t, Hibernate uses whatever else is available:
BIT
, TINYINT
, or SMALLINT
.
Example 15. Implicit boolean mapping
// this will be mapped to BIT or BOOLEAN on the database
@Basic
boolean implicit;
However, it is quite common to find boolean values encoded as a character or as an integer.
Such cases are exactly the intention of AttributeConverter
. For convenience, Hibernate
provides 3 built-in converters for the common boolean mapping cases:
-
YesNoConverter
encodes a boolean value as'Y'
or'N'
, -
TrueFalseConverter
encodes a boolean value as'T'
or'F'
, and -
NumericBooleanConverter
encodes the value as an integer,1
for true, and0
for false.
Example 16. Using AttributeConverter
// this will get mapped to CHAR or NCHAR with a conversion
@Basic
@Convert(converter = org.hibernate.type.YesNoConverter.class)
boolean convertedYesNo;
// this will get mapped to CHAR or NCHAR with a conversion
@Basic
@Convert(converter = org.hibernate.type.TrueFalseConverter.class)
boolean convertedTrueFalse;
// this will get mapped to TINYINT with a conversion
@Basic
@Convert(converter = org.hibernate.type.NumericBooleanConverter.class)
boolean convertedNumeric;
If the boolean value is defined in the database as something other than BOOLEAN
, character or integer,
the value can also be mapped using a custom AttributeConverter
— see AttributeConverters.
A UserType
may also be used — see Custom type mapping
2.2.7. Byte
By default, Hibernate maps values of Byte
/ byte
to the TINYINT
JDBC type.
Example 17. Mapping Byte
// these will both be mapped using TINYINT
Byte wrapper;
byte primitive;
See Byte array for mapping arrays of bytes.
2.2.8. Short
By default, Hibernate maps values of Short
/ short
to the SMALLINT
JDBC type.
Example 18. Mapping Short
// these will both be mapped using SMALLINT
Short wrapper;
short primitive;
2.2.9. Integer
By default, Hibernate maps values of Integer
/ int
to the INTEGER
JDBC type.
Example 19. Mapping Integer
// these will both be mapped using INTEGER
Integer wrapper;
int primitive;
2.2.10. Long
By default, Hibernate maps values of Long
/ long
to the BIGINT
JDBC type.
Example 20. Mapping Long
// these will both be mapped using BIGINT
Long wrapper;
long primitive;
2.2.11. BigInteger
By default, Hibernate maps values of BigInteger
to the NUMERIC
JDBC type.
Example 21. Mapping BigInteger
// will be mapped using NUMERIC
BigInteger wrapper;
2.2.12. Double
By default, Hibernate maps values of Double
to the DOUBLE
, FLOAT
, REAL
or
NUMERIC
JDBC type depending on the capabilities of the database
Example 22. Mapping Double
// these will be mapped using DOUBLE, FLOAT, REAL or NUMERIC
// depending on the capabilities of the database
Double wrapper;
double primitive;
A specific type can be influenced using any of the JDBC type influencers covered in
JdbcType section.
If @JdbcTypeCode
is used, the Dialect is still consulted to make sure the database
supports the requested type. If not, an appropriate type is selected
2.2.13. Float
By default, Hibernate maps values of Float
to the FLOAT
, REAL
or
NUMERIC
JDBC type depending on the capabilities of the database.
Example 23. Mapping Float
// these will be mapped using FLOAT, REAL or NUMERIC
// depending on the capabilities of the database
Float wrapper;
float primitive;
A specific type can be influenced using any of the JDBC type influencers covered in
Mapping basic values section.
If @JdbcTypeCode
is used, the Dialect is still consulted to make sure the database
supports the requested type. If not, an appropriate type is selected
2.2.14. BigDecimal
By default, Hibernate maps values of BigDecimal
to the NUMERIC
JDBC type.
Example 24. Mapping BigDecimal
// will be mapped using NUMERIC
BigDecimal wrapper;
2.2.15. Character
By default, Hibernate maps Character
to the CHAR
JDBC type.
Example 25. Mapping Character
// these will be mapped using CHAR
Character wrapper;
char primitive;
2.2.16. String
By default, Hibernate maps String
to the VARCHAR
JDBC type.
Example 26. Mapping String
// will be mapped using VARCHAR
String string;
// will be mapped using CLOB
@Lob
String clobString;
Optionally, you may specify the maximum length of the string using @Column(length=…)
,
or using the @Size
annotation from Hibernate Validator.
For very large strings, you can use one of the constant values defined by the class
org.hibernate.Length
, for example:
@Column(length=Length.LONG)
private String text;
Alternatively, you may explicitly specify the JDBC type LONGVARCHAR
, which is treated
as a VARCHAR
mapping with default length=Length.LONG
when no length
is explicitly
specified:
@JdbcTypeCode(Types.LONGVARCHAR)
private String text;
If you use Hibernate for schema generation, Hibernate will generate DDL with a column type
that is large enough to accommodate the maximum length you’ve specified.
If the maximum length you specify is too long to fit in the largest |
See Handling LOB data for details on mapping to a database CLOB.
For databases which support nationalized character sets, you can also store strings as
nationalized data.
Example 27. Mapping String as nationalized
// will be mapped using NVARCHAR
@Nationalized
String nstring;
// will be mapped using NCLOB
@Lob
@Nationalized
String nclobString;
See Handling nationalized character data for details on mapping strings using nationalized character sets.
2.2.17. Character arrays
By default, Hibernate maps char[]
to the VARCHAR
JDBC type.
Since Character[]
can contain null elements, it is mapped as basic array type instead.
Prior to Hibernate 6.2, also Character[]
mapped to VARCHAR
, yet disallowed null
elements.
To continue mapping Character[]
to the VARCHAR
JDBC type, or for LOBs mapping to the CLOB
JDBC type,
it is necessary to annotate the persistent attribute with @JavaType( CharacterArrayJavaType.class )
.
Example 28. Mapping Character
// mapped as VARCHAR
char[] primitive;
Character[] wrapper;
@JavaType( CharacterArrayJavaType.class )
Character[] wrapperOld;
// mapped as CLOB
@Lob
char[] primitiveClob;
@Lob
Character[] wrapperClob;
See Handling LOB data for details on mapping as database LOB.
For databases which support nationalized character sets, you can also store character arrays as
nationalized data.
Example 29. Mapping character arrays as nationalized
// mapped as NVARCHAR
@Nationalized
char[] primitiveNVarchar;
@Nationalized
Character[] wrapperNVarchar;
@Nationalized
@JavaType( CharacterArrayJavaType.class )
Character[] wrapperNVarcharOld;
// mapped as NCLOB
@Lob
@Nationalized
char[] primitiveNClob;
@Lob
@Nationalized
Character[] wrapperNClob;
See Handling nationalized character data for details on mapping strings using nationalized character sets.
2.2.18. Clob / NClob
Be sure to check out Handling LOB data which covers basics of LOB handling and Handling nationalized character data which covers basics |
By default, Hibernate will map the java.sql.Clob
Java type to CLOB
and java.sql.NClob
to NCLOB
.
Considering we have the following database table:
Example 30. CLOB — SQL
CREATE TABLE Product (
id INTEGER NOT NULL,
name VARCHAR(255),
warranty CLOB,
PRIMARY KEY (id)
)
Let’s first map this using the @Lob
Jakarta Persistence annotation and the java.sql.Clob
type:
Example 31. CLOB
mapped to java.sql.Clob
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
private Clob warranty;
//Getters and setters are omitted for brevity
}
To persist such an entity, you have to create a Clob
using the ClobProxy
Hibernate utility:
Example 32. Persisting a java.sql.Clob
entity
String warranty = "My product warranty";
final Product product = new Product();
product.setId(1);
product.setName("Mobile phone");
product.setWarranty(ClobProxy.generateProxy(warranty));
entityManager.persist(product);
To retrieve the Clob
content, you need to transform the underlying java.io.Reader
:
Example 33. Returning a java.sql.Clob
entity
Product product = entityManager.find(Product.class, productId);
try (Reader reader = product.getWarranty().getCharacterStream()) {
assertEquals("My product warranty", toString(reader));
}
We could also map the CLOB in a materialized form. This way, we can either use a String
or a char[]
.
Example 34. CLOB
mapped to String
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
private String warranty;
//Getters and setters are omitted for brevity
}
We might even want the materialized data as a char array.
Example 35. CLOB — materialized char[]
mapping
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
private char[] warranty;
//Getters and setters are omitted for brevity
}
Just like with CLOB
, Hibernate can also deal with NCLOB
SQL data types:
Example 36. NCLOB
— SQL
CREATE TABLE Product (
id INTEGER NOT NULL ,
name VARCHAR(255) ,
warranty nclob ,
PRIMARY KEY ( id )
)
Hibernate can map the NCLOB
to a java.sql.NClob
Example 37. NCLOB
mapped to java.sql.NClob
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
@Nationalized
// Clob also works, because NClob extends Clob.
// The database type is still NCLOB either way and handled as such.
private NClob warranty;
//Getters and setters are omitted for brevity
}
To persist such an entity, you have to create an NClob
using the NClobProxy
Hibernate utility:
Example 38. Persisting a java.sql.NClob
entity
String warranty = "My product warranty";
final Product product = new Product();
product.setId(1);
product.setName("Mobile phone");
product.setWarranty(NClobProxy.generateProxy(warranty));
entityManager.persist(product);
To retrieve the NClob
content, you need to transform the underlying java.io.Reader
:
Example 39. Returning a java.sql.NClob
entity
Product product = entityManager.find(Product.class, 1);
try (Reader reader = product.getWarranty().getCharacterStream()) {
assertEquals("My product warranty", toString(reader));
}
We could also map the NCLOB
in a materialized form. This way, we can either use a String
or a char[]
.
Example 40. NCLOB
mapped to String
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
@Nationalized
private String warranty;
//Getters and setters are omitted for brevity
}
We might even want the materialized data as a char array.
Example 41. NCLOB — materialized char[]
mapping
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
@Nationalized
private char[] warranty;
//Getters and setters are omitted for brevity
}
2.2.19. Byte array
By default, Hibernate maps byte[]
to the VARBINARY
JDBC type.
Since Byte[]
can contain null elements, it is mapped as basic array type instead.
Prior to Hibernate 6.2, also Byte[]
mapped to VARBINARY
, yet disallowed null
elements.
To continue mapping Byte[]
to the VARBINARY
JDBC type, or for LOBs mapping to the BLOB
JDBC type,
it is necessary to annotate the persistent attribute with @JavaType( ByteArrayJavaType.class )
.
Example 42. Mapping arrays of bytes
// mapped as VARBINARY
private byte[] primitive;
private Byte[] wrapper;
@JavaType( ByteArrayJavaType.class )
private Byte[] wrapperOld;
// mapped as (materialized) BLOB
@Lob
private byte[] primitiveLob;
@Lob
private Byte[] wrapperLob;
Just like with strings, you may specify the maximum length using @Column(length=…)
or the @Size
annotation from Hibernate Validator.
For very large arrays, you can use the constants defined by org.hibernate.Length
.
Alternatively @JdbcTypeCode(Types.LONGVARBINARY)
is treated as a VARBINARY
mapping
with default length=Length.LONG
when no length is explicitly specified.
If you use Hibernate for schema generation, Hibernate will generate DDL with a column type
that is large enough to accommodate the maximum length you’ve specified.
If the maximum length you specify is too long to fit in the largest |
See Handling LOB data for details on mapping to a database BLOB.
2.2.20. Blob
Be sure to check out Handling LOB data which covers basics of LOB handling. |
By default, Hibernate will map the java.sql.Blob
Java type to BLOB
.
Considering we have the following database table:
Example 43. BLOB — SQL
CREATE TABLE Product (
id INTEGER NOT NULL ,
image blob ,
name VARCHAR(255) ,
PRIMARY KEY ( id )
)
Let’s first map this using the JDBC java.sql.Blob
type.
Example 44. BLOB
mapped to java.sql.Blob
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
private Blob image;
//Getters and setters are omitted for brevity
}
To persist such an entity, you have to create a Blob
using the BlobProxy
Hibernate utility:
Example 45. Persisting a java.sql.Blob
entity
byte[] image = new byte[] {1, 2, 3};
final Product product = new Product();
product.setId(1);
product.setName("Mobile phone");
product.setImage(BlobProxy.generateProxy(image));
entityManager.persist(product);
To retrieve the Blob
content, you need to transform the underlying java.io.InputStream
:
Example 46. Returning a java.sql.Blob
entity
Product product = entityManager.find(Product.class, productId);
try (InputStream inputStream = product.getImage().getBinaryStream()) {
assertArrayEquals(new byte[] {1, 2, 3}, toBytes(inputStream));
}
We could also map the BLOB in a materialized form (e.g. byte[]
).
Example 47. BLOB
mapped to byte[]
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Lob
private byte[] image;
//Getters and setters are omitted for brevity
}
2.2.21. Duration
By default, Hibernate maps Duration
to the NUMERIC
SQL type.
It’s possible to map Duration to the INTERVAL_SECOND SQL type using @JdbcTypeCode(INTERVAL_SECOND) or by setting hibernate.type.preferred_duration_jdbc_type=INTERVAL_SECOND
|
Example 48. Mapping Duration
private Duration duration;
2.2.22. Instant
Instant
is mapped to the TIMESTAMP_UTC
SQL type.
Example 49. Mapping Instant
// mapped as TIMESTAMP
private Instant instant;
See Handling temporal data for basics of temporal mapping
2.2.23. LocalDate
LocalDate
is mapped to the DATE
JDBC type.
Example 50. Mapping LocalDate
// mapped as DATE
private LocalDate localDate;
See Handling temporal data for basics of temporal mapping
2.2.24. LocalDateTime
LocalDateTime
is mapped to the TIMESTAMP
JDBC type.
Example 51. Mapping LocalDateTime
// mapped as TIMESTAMP
private LocalDateTime localDateTime;
See Handling temporal data for basics of temporal mapping
2.2.25. LocalTime
LocalTime
is mapped to the TIME
JDBC type.
Example 52. Mapping LocalTime
// mapped as TIME
private LocalTime localTime;
See Handling temporal data for basics of temporal mapping
2.2.26. OffsetDateTime
OffsetDateTime
is mapped to the TIMESTAMP
or TIMESTAMP_WITH_TIMEZONE
JDBC type
depending on the database.
Example 53. Mapping OffsetDateTime
// mapped as TIMESTAMP or TIMESTAMP_WITH_TIMEZONE
private OffsetDateTime offsetDateTime;
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.27. OffsetTime
OffsetTime
is mapped to the TIME
or TIME_WITH_TIMEZONE
JDBC type
depending on the database.
Example 54. Mapping OffsetTime
// mapped as TIME or TIME_WITH_TIMEZONE
private OffsetTime offsetTime;
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.28. TimeZone
TimeZone
is mapped to VARCHAR
JDBC type.
Example 55. Mapping OffsetTime
// mapped as VARCHAR
private TimeZone timeZone;
2.2.29. ZonedDateTime
ZonedDateTime
is mapped to the TIMESTAMP
or TIMESTAMP_WITH_TIMEZONE
JDBC type
depending on the database.
Example 56. Mapping ZonedDateTime
// mapped as TIMESTAMP or TIMESTAMP_WITH_TIMEZONE
private ZonedDateTime zonedDateTime;
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.30. ZoneOffset
ZoneOffset
is mapped to VARCHAR
JDBC type.
Example 57. Mapping ZoneOffset
// mapped as VARCHAR
private ZoneOffset zoneOffset;
2.2.31. Calendar
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.32. Date
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.33. Time
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.34. Timestamp
See Handling temporal data for basics of temporal mapping
See Using a specific time zone for basics of time-zone handling
2.2.35. Class
Hibernate maps Class
references to VARCHAR
JDBC type
Example 58. Mapping Class
// mapped as VARCHAR
private Class<?> clazz;
2.2.36. Currency
Hibernate maps Currency
references to VARCHAR
JDBC type
Example 59. Mapping Currency
// mapped as VARCHAR
private Currency currency;
2.2.37. Locale
Hibernate maps Locale
references to VARCHAR
JDBC type
Example 60. Mapping Locale
// mapped as VARCHAR
private Locale locale;
2.2.38. UUID
Hibernate allows mapping UUID values in a number of ways. By default, Hibernate will
store UUID values in the native form by using the SQL type UUID
or in binary form with the BINARY
JDBC type
if the database does not have a native UUID type.
The default uses the binary representation because it uses a more efficient column storage. However, many applications prefer the readability of the character-based column storage. To switch the default mapping, set the |
UUID as binary
As mentioned, the default mapping for UUID attributes.
Maps the UUID to a byte[]
using java.util.UUID#getMostSignificantBits
and java.util.UUID#getLeastSignificantBits
and stores that as BINARY
data.
Chosen as the default simply because it is generally more efficient from a storage perspective.
UUID as (var)char
Maps the UUID to a String using java.util.UUID#toString
and java.util.UUID#fromString
and stores that as CHAR
or VARCHAR
data.
UUID as identifier
Hibernate supports using UUID values as identifiers, and they can even be generated on the user’s behalf.
For details, see the discussion of generators in Identifiers.
2.2.39. InetAddress
By default, Hibernate will map InetAddress
to the INET
SQL type and fallback to BINARY
if necessary.
Example 61. Mapping InetAddress
private InetAddress address;
2.2.40. JSON mapping
Hibernate will only use the JSON
type if explicitly configured through @JdbcTypeCode( SqlTypes.JSON )
.
The JSON library used for serialization/deserialization is detected automatically,
but can be overridden by setting hibernate.type.json_format_mapper
as can be read in the Configurations section.
Example 62. Mapping JSON
@JdbcTypeCode( SqlTypes.JSON )
private Map<String, String> stringMap;
2.2.41. XML mapping
Hibernate will only use the XML
type if explicitly configured through @JdbcTypeCode( SqlTypes.SQLXML )
.
The XML library used for serialization/deserialization is detected automatically,
but can be overridden by setting hibernate.type.xml_format_mapper
as can be read in the Configurations section.
Example 63. Mapping XML
@JdbcTypeCode( SqlTypes.SQLXML )
private Map<String, StringNode> stringMap;
2.2.42. Basic array mapping
Basic arrays, other than byte[]
/Byte[] and char[]
/Character[]
, map to the type code SqlTypes.ARRAY
by default,
which maps to the SQL standard array
type if possible,
as determined via the new methods getArrayTypeName
and supportsStandardArrays
of org.hibernate.dialect.Dialect
.
If SQL standard array types are not available, data will be modeled as SqlTypes.JSON
, SqlTypes.XML
or SqlTypes.VARBINARY
,
depending on the database support as determined via the new method org.hibernate.dialect.Dialect.getPreferredSqlTypeCodeForArray
.
Example 64. Mapping basic arrays
Short[] wrapper;
short[] primitive;
2.2.43. Basic collection mapping
Basic collections (only subtypes of Collection
), which are not annotated with @ElementCollection
,
map to the type code SqlTypes.ARRAY
by default, which maps to the SQL standard array
type if possible,
as determined via the new methods getArrayTypeName
and supportsStandardArrays
of org.hibernate.dialect.Dialect
.
If SQL standard array types are not available, data will be modeled as SqlTypes.JSON
, SqlTypes.XML
or SqlTypes.VARBINARY
,
depending on the database support as determined via the new method org.hibernate.dialect.Dialect.getPreferredSqlTypeCodeForArray
.
Example 65. Mapping basic collections
List<Short> list;
SortedSet<Short> sortedSet;
2.2.44. Compositional basic mapping
The compositional approach allows defining how the mapping should work in terms of influencing
individual parts that make up a basic-value mapping. This section will look at these individual
parts and the specifics of influencing each.
JavaType
Hibernate needs to understand certain aspects of the Java type to handle values properly and efficiently.
Hibernate understands these capabilities through its org.hibernate.type.descriptor.java.JavaType
contract.
Hibernate provides built-in support for many JDK types (Integer
, String
, e.g.), but also supports the ability
for the application to change the handling for any of the standard JavaType
registrations as well as
add in handling for non-standard types. Hibernate provides multiple ways for the application to influence
the JavaType
descriptor to use.
The resolution can be influenced locally using the @JavaType
annotation on a particular mapping. The
indicated descriptor will be used just for that mapping. There are also forms of @JavaType
for influencing
the keys of a Map (@MapKeyJavaType
), the index of a List or array (@ListIndexJavaType
), the identifier
of an ID-BAG mapping (@CollectionIdJavaType
) as well as the discriminator (@AnyDiscriminator
) and
key (@AnyKeyJavaClass
, @AnyKeyJavaType
) of an ANY mapping.
The resolution can also be influenced globally by registering the appropriate JavaType
descriptor with the
JavaTypeRegistry
. This approach is able to both «override» the handling for certain Java types or
to register new types. See Registries for discussion of JavaTypeRegistry
.
See Resolving the composition for a discussion of the process used to resolve the
mapping composition.
JdbcType
Hibernate also needs to understand aspects of the JDBC type it should use (how it should bind values,
how it should extract values, etc.) which is the role of its org.hibernate.type.descriptor.jdbc.JdbcType
contract. Hibernate provides multiple ways for the application to influence the JdbcType
descriptor to use.
Locally, the resolution can be influenced using either the @JdbcType
or @JdbcTypeCode
annotations. There
are also annotations for influencing the JdbcType
in relation to Map keys (@MapKeyJdbcType
, @MapKeyJdbcTypeCode
),
the index of a List or array (@ListIndexJdbcType
, @ListIndexJdbcTypeCode
), the identifier of an ID-BAG mapping
(@CollectionIdJdbcType
, @CollectionIdJdbcTypeCode
) as well as the key of an ANY mapping (@AnyKeyJdbcType
,
@AnyKeyJdbcTypeCode
). The @JdbcType
specifies a specific JdbcType
implementation to use while @JdbcTypeCode
specifies a «code» that is then resolved against the JdbcTypeRegistry
.
The «type code» relative to a |
Customizing the JdbcTypeRegistry
can be accomplished through @JdbcTypeRegistration
and
TypeContributor
. See Registries for discussion of JavaTypeRegistry
.
See TypeContributor for discussion of TypeContributor
.
See the @JdbcTypeCode
Javadoc for details.
See Resolving the composition for a discussion of the process used to resolve the
mapping composition.
MutabilityPlan
MutabilityPlan
is the means by which Hibernate understands how to deal with the domain value in terms
of its internal mutability as well as related concerns such as making copies. While it seems like a minor
concern, it can have a major impact on performance. See AttributeConverter
Mutability Plan for one case where
this can manifest. See also Case Study : BitSet for another discussion.
The MutabilityPlan
for a mapping can be influenced by any of the following annotations:
-
@Mutability
-
@Immutable
-
@MapKeyMutability
-
@CollectionIdMutability
Hibernate checks the following places for @Mutability
and @Immutable
, in order of precedence:
-
Local to the mapping
-
On the associated
AttributeConverter
implementation class (if one) -
On the value’s Java type
In most cases, the fallback defined by JavaType#getMutabilityPlan
is the proper strategy.
Hibernate uses MutabilityPlan
to:
-
Check whether a value is considered dirty
-
Make deep copies
-
Marshal values to and from the second-level cache
Generally speaking, immutable values perform better in all of these cases
-
To check for dirtiness, Hibernate just needs to check object identity (
==
) as opposed
to equality (Object#equals
). -
The same value instance can be used as the deep copy of itself.
-
The same value can be used from the second-level cache as well as the value we put into the
second-level cache.
If a particular Java type is considered mutable (a Date
e.g.), @Immutable
or a immutable-specific
MutabilityPlan
implementation can be specified to have Hibernate treat the value as immutable. This
also acts as a contract from the application that the internal state of these objects is not changed
by the application. Specifying that a mutable type is immutable and then changing the internal state
will lead to problems; so only do this if the application unequivocally does not change the internal
state.
See Resolving the composition for a discussion of the process used to resolve the
mapping composition.
BasicValueConverter
BasicValueConverter
is roughly analogous to AttributeConverter
in that it describes a conversion to
happen when reading or writing values of a basic-valued model part. In fact, internally Hibernate wraps
an applied AttributeConverter
in a BasicValueConverter
. It also applies implicit BasicValueConverter
converters in certain cases such as enum handling, etc.
Hibernate does not provide an explicit facility to influence these conversions beyond AttributeConverter
.
See AttributeConverters.
See Resolving the composition for a discussion of the process used to resolve the
mapping composition.
Resolving the composition
Using this composition approach, Hibernate will need to resolve certain parts of this mapping. Often
this involves «filling in the blanks» as it will be configured for just parts of the mapping. This section
outlines how this resolution happens.
This is a complicated process and is only covered at a high level for the most common cases here. For the full specifics, consult the source code for |
First, we look for a custom type. If found, this takes predence. See Custom type mapping for details
If an AttributeConverter
is applied, we use it as the basis for the resolution
-
If
@JavaType
is also used, that specificJavaType
is used for the converter’s «domain type». Otherwise,
the Java type defined by the converter as its «domain type» is resolved against theJavaTypeRegistry
-
If
@JdbcType
or@JdbcTypeCode
is used, the indicatedJdbcType
is used and the converted «relational Java
type» is determined byJdbcType#getJdbcRecommendedJavaTypeMapping
. Otherwise, the Java type defined by the
converter as its relational type is used and theJdbcType
is determined byJdbcType#getRecommendedJdbcType
-
The
MutabilityPlan
can be specified using@Mutability
or@Immutable
on theAttributeConverter
implementation,
the basic value mapping or the Java type used as the domain-type. Otherwise,JdbcType#getJdbcRecommendedJavaTypeMapping
for the conversion’s domain-type is used to determine the mutability-plan.
Next we try to resolve the JavaType
to use for the mapping. We check for an explicit @JavaType
and use the specified
JavaType
if found. Next any «implicit» indication is checked; for example, the index for a List has the implicit Java type
of Integer
. Next, we use reflection if possible. If we are unable to determine the JavaType
to use through the preceeding
steps, we try to resolve an explicitly specified JdbcType
to use and, if found, use its
JdbcType#getJdbcRecommendedJavaTypeMapping
as the mapping’s JavaType
. If we are not able to determine the
JavaType
by this point, an error is thrown.
The JavaType
resolved earlier is then inspected for a number of special cases.
-
For enum values, we check for an explicit
@Enumerated
and create an enumeration mapping. Note that this resolution
still uses any explicitJdbcType
indicators -
For temporal values, we check for
@Temporal
and create an enumeration mapping. Note that this resolution
still uses any explicitJdbcType
indicators; this includes@JdbcType
and@JdbcTypeCode
, as well as
@TimeZoneStorage
and@TimeZoneColumn
if appropriate.
The fallback at this point is to use the JavaType
and JdbcType
determined in earlier steps to create a
JDBC-mapping (which encapsulates the JavaType
and JdbcType
) and combines it with the resolved MutabilityPlan
When using the compositional approach, there are other ways to influence the resolution as covered
in Enums, Handling temporal data, Handling LOB data and Handling nationalized character data
See TypeContributor for an alternative to @JavaTypeRegistration
and @JdbcTypeRegistration
.
2.2.45. Custom type mapping
Another approach is to supply the implementation of the org.hibernate.usertype.UserType
contract using @Type
.
There are also corresponding, specialized forms of @Type
for specific model parts:
-
When mapping a Map,
@Type
describes the Map value while@MapKeyType
describe the Map key -
When mapping an id-bag,
@Type
describes the elements while@CollectionIdType
describes the collection-id -
For other collection mappings,
@Type
describes the elements -
For discriminated association mappings (
@Any
and@ManyToAny
),@Type
describes the discriminator value
@Type
allows for more complex mapping concerns; but, AttributeConverter and
Compositional basic mapping should generally be preferred as simpler solutions
2.2.46. Handling nationalized character data
How nationalized character data is handled and stored depends on the underlying database.
Most databases support storing nationalized character data through the standardized SQL
NCHAR, NVARCHAR, LONGNVARCHAR and NCLOB variants.
Others support storing nationalized data as part of CHAR, VARCHAR, LONGVARCHAR
and CLOB. Generally these databases do not support NCHAR, NVARCHAR, LONGNVARCHAR
and NCLOB, even as aliased types.
Ultimately Hibernate understands this through Dialect#getNationalizationSupport()
To ensure nationalized character data gets stored and accessed correctly, @Nationalized
can be used locally or hibernate.use_nationalized_character_data
can be set globally.
|
For databases with no See also Handling LOB data regarding similar limitation for databases which do not support |
Considering we have the following database table:
Example 66. NVARCHAR
— SQL
CREATE TABLE Product (
id INTEGER NOT NULL ,
name VARCHAR(255) ,
warranty NVARCHAR(255) ,
PRIMARY KEY ( id )
)
To map a specific attribute to a nationalized variant data type, Hibernate defines the @Nationalized
annotation.
Example 67. NVARCHAR
mapping
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private String name;
@Nationalized
private String warranty;
//Getters and setters are omitted for brevity
}
2.2.47. Handling LOB data
The @Lob
annotation specifies that character or binary data should be written to the database
using the special JDBC APIs for handling database LOB (Large OBject) types.
How JDBC deals with Some database drivers (i.e. PostgreSQL) are especially problematic and in such cases you might |
For databases with no |
There’s two ways a LOB may be represented in the Java domain model:
-
using a special JDBC-defined LOB locator type, or
-
using a regular «materialized» type like
String
,char[]
, orbyte[]
.
LOB Locator
The JDBC LOB locator types are:
-
java.sql.Blob
-
java.sql.Clob
-
java.sql.NClob
These types represent references to off-table LOB data.
In principle, they allow JDBC drivers to support more efficient access to the LOB data.
Some drivers stream parts of the LOB data as needed, potentially consuming less memory.
However, java.sql.Blob
and java.sql.Clob
can be unnatural to deal with and suffer
certain limitations.
For example, it’s not portable to access a LOB locator after the end of the transaction
in which it was obtained.
Materialized LOB
Alternatively, Hibernate lets you access LOB data via the familiar Java types String
,
char[]
, and byte[]
. But of course this requires materializing the entire contents
of the LOB in memory when the object is first retrieved. Whether this performance cost
is acceptable depends on many factors, including the vagaries of the JDBC driver.
You don’t need to use a |
2.2.48. Handling temporal data
Hibernate supports mapping temporal values in numerous ways, though ultimately these strategies
boil down to the 3 main Date/Time types defined by the SQL specification:
- DATE
-
Represents a calendar date by storing years, months and days.
- TIME
-
Represents the time of a day by storing hours, minutes and seconds.
- TIMESTAMP
-
Represents both a DATE and a TIME plus nanoseconds.
- TIMESTAMP WITH TIME ZONE
-
Represents both a DATE and a TIME plus nanoseconds and zone id or offset.
The mapping of java.time
temporal types to the specific SQL Date/Time types is implied as follows:
- DATE
-
java.time.LocalDate
- TIME
-
java.time.LocalTime
,java.time.OffsetTime
- TIMESTAMP
-
java.time.Instant
,java.time.LocalDateTime
,java.time.OffsetDateTime
andjava.time.ZonedDateTime
- TIMESTAMP WITH TIME ZONE
-
java.time.OffsetDateTime
,java.time.ZonedDateTime
Although Hibernate recommends the use of the java.time
package for representing temporal values,
it does support using java.sql.Date
, java.sql.Time
, java.sql.Timestamp
, java.util.Date
and
java.util.Calendar
.
The mappings for java.sql.Date
, java.sql.Time
, java.sql.Timestamp
are implicit:
- DATE
-
java.sql.Date
- TIME
-
java.sql.Time
- TIMESTAMP
-
java.sql.Timestamp
Applying |
When using java.util.Date
or java.util.Calendar
, Hibernate assumes TIMESTAMP
. To alter that,
use @Temporal
.
Example 68. Mapping java.util.Date
// mapped as TIMESTAMP by default
Date dateAsTimestamp;
// explicitly mapped as DATE
@Temporal(TemporalType.DATE)
Date dateAsDate;
// explicitly mapped as TIME
@Temporal(TemporalType.TIME)
Date dateAsTime;
Using a specific time zone
When the time zone is not specified, the JDBC driver is going to use the underlying JVM default time zone, which might not be suitable if the application is used from all across the globe.
For this reason, it is very common to use a single reference time zone (e.g. UTC) whenever saving/loading data from the database.
One alternative would be to configure all JVMs to use the reference time zone:
- Declaratively
-
java -Duser.timezone=UTC ...
- Programmatically
-
TimeZone.setDefault( TimeZone.getTimeZone( "UTC" ) );
However, as explained in this article, this is not always practical, especially for front-end nodes.
For this reason, Hibernate offers the hibernate.jdbc.time_zone
configuration property which can be configured:
- Declaratively, at the
SessionFactory
level -
settings.put( AvailableSettings.JDBC_TIME_ZONE, TimeZone.getTimeZone( "UTC" ) );
- Programmatically, on a per
Session
basis -
Session session = sessionFactory() .withOptions() .jdbcTimeZone( TimeZone.getTimeZone( "UTC" ) ) .openSession();
Handling time zoned temporal data
By default, Hibernate will convert and normalize OffsetDateTime
and ZonedDateTime
to java.sql.Timestamp
in UTC.
This behavior can be altered by configuring the hibernate.timezone.default_storage
property
settings.put(
AvailableSettings.TIMEZONE_DEFAULT_STORAGE,
TimeZoneStorageType.AUTO
);
Other possible storage types are AUTO
, COLUMN
, NATIVE
and NORMALIZE
(the default).
With COLUMN
, Hibernate will save the time zone information into a dedicated column,
whereas NATIVE
will require the support of database for a TIMESTAMP WITH TIME ZONE
data type
that retains the time zone information.
NORMALIZE
doesn’t store time zone information and will simply convert the timestamp to UTC.
Hibernate understands what a database/dialect supports through Dialect#getTimeZoneSupport
and will abort with a boot error if the NATIVE
is used in conjunction with a database that doesn’t support this.
For AUTO
, Hibernate tries to use NATIVE
if possible and falls back to COLUMN
otherwise.
2.2.49. @TimeZoneStorage
Hibernate supports defining the storage to use for time zone information for individual properties
via the @TimeZoneStorage
and @TimeZoneColumn
annotations.
The storage type can be specified via the @TimeZoneStorage
by specifying a org.hibernate.annotations.TimeZoneStorageType
.
The default storage type is AUTO
which will ensure that the time zone information is retained.
The @TimeZoneColumn
annotation can be used in conjunction with AUTO
or COLUMN
and allows to define
the column details for the time zone information storage.
Storing the zone offset might be problematic for future timestamps as zone rules can change. |
Example 69. @TimeZoneColumn
usage
@TimeZoneStorage(TimeZoneStorageType.COLUMN)
@TimeZoneColumn(name = "birthtime_offset_offset")
@Column(name = "birthtime_offset")
private OffsetTime offsetTimeColumn;
@TimeZoneStorage(TimeZoneStorageType.COLUMN)
@TimeZoneColumn(name = "birthday_offset_offset")
@Column(name = "birthday_offset")
private OffsetDateTime offsetDateTimeColumn;
@TimeZoneStorage(TimeZoneStorageType.COLUMN)
@TimeZoneColumn(name = "birthday_zoned_offset")
@Column(name = "birthday_zoned")
private ZonedDateTime zonedDateTimeColumn;
2.2.50. AttributeConverters
With a custom AttributeConverter
, the application developer can map a given JDBC type to an entity basic type.
In the following example, the java.time.Period
is going to be mapped to a VARCHAR
database column.
Example 70. java.time.Period
custom AttributeConverter
@Converter
public class PeriodStringConverter
implements AttributeConverter<Period, String> {
@Override
public String convertToDatabaseColumn(Period attribute) {
return attribute.toString();
}
@Override
public Period convertToEntityAttribute(String dbData) {
return Period.parse(dbData);
}
}
To make use of this custom converter, the @Convert
annotation must decorate the entity attribute.
Example 71. Entity using the custom java.time.Period
AttributeConverter
mapping
@Entity(name = "Event")
public static class Event {
@Id
@GeneratedValue
private Long id;
@Convert(converter = PeriodStringConverter.class)
@Column(columnDefinition = "")
private Period span;
//Getters and setters are omitted for brevity
}
When persisting such entity, Hibernate will do the type conversion based on the AttributeConverter
logic:
Example 72. Persisting entity using the custom AttributeConverter
INSERT INTO Event ( span, id )
VALUES ( 'P1Y2M3D', 1 )
An AttributeConverter
can be applied globally for (@Converter( autoApply=true )
) or locally.
AttributeConverter
Java and JDBC types
In cases when the Java type specified for the «database side» of the conversion (the second AttributeConverter
bind parameter) is not known,
Hibernate will fallback to a java.io.Serializable
type.
If the Java type is not known to Hibernate, you will encounter the following message:
HHH000481: Encountered Java type for which we could not locate a JavaType and which does not appear to implement equals and/or hashCode.
This can lead to significant performance problems when performing equality/dirty checking involving this Java type.
Consider registering a custom JavaType or at least implementing equals/hashCode.
A Java type is «known» if it has an entry in the JavaTypeRegistry
. While Hibernate does load many JDK types into
the JavaTypeRegistry
, an application can also expand the JavaTypeRegistry
by adding new JavaType
entries as discussed in Compositional basic mapping and TypeContributor.
Mapping an AttributeConverter using HBM mappings
When using HBM mappings, you can still make use of the Jakarta Persistence AttributeConverter
because Hibernate supports
such mapping via the type
attribute as demonstrated by the following example.
Let’s consider we have an application-specific Money
type:
Example 73. Application-specific Money
type
public class Money {
private long cents;
public Money(long cents) {
this.cents = cents;
}
public long getCents() {
return cents;
}
public void setCents(long cents) {
this.cents = cents;
}
}
Now, we want to use the Money
type when mapping the Account
entity:
Example 74. Account
entity using the Money
type
public class Account {
private Long id;
private String owner;
private Money balance;
//Getters and setters are omitted for brevity
}
Since Hibernate has no knowledge how to persist the Money
type, we could use a Jakarta Persistence AttributeConverter
to transform the Money
type as a Long
. For this purpose, we are going to use the following
MoneyConverter
utility:
Example 75. MoneyConverter
implementing the Jakarta Persistence AttributeConverter
interface
public class MoneyConverter
implements AttributeConverter<Money, Long> {
@Override
public Long convertToDatabaseColumn(Money attribute) {
return attribute == null ? null : attribute.getCents();
}
@Override
public Money convertToEntityAttribute(Long dbData) {
return dbData == null ? null : new Money(dbData);
}
}
To map the MoneyConverter
using HBM configuration files you need to use the converted::
prefix in the type
attribute of the property
element.
Example 76. HBM mapping for AttributeConverter
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="org.hibernate.orm.test.mapping.converter.hbm">
<class name="org.hibernate.orm.test.mapping.converter.hbm.Account" table="account" >
<id name="id"/>
<property name="owner"/>
<property name="balance"
type="converted::org.hibernate.orm.test.mapping.converter.hbm.MoneyConverter"/>
</class>
</hibernate-mapping>
AttributeConverter
Mutability Plan
A basic type that’s converted by a Jakarta Persistence AttributeConverter
is immutable if the underlying Java type is immutable
and is mutable if the associated attribute type is mutable as well.
Therefore, mutability is given by the JavaType#getMutabilityPlan
of the associated entity attribute type.
This can be adjusted by using @Immutable
or @Mutability
on any of:
-
the basic value
-
the
AttributeConverter
class -
the basic value type
See Mapping basic values for additional details.
Immutable types
If the entity attribute is a String
, a primitive wrapper (e.g. Integer
, Long
), an Enum type, or any other immutable Object
type,
then you can only change the entity attribute value by reassigning it to a new value.
Considering we have the same Period
entity attribute as illustrated in the AttributeConverters section:
@Entity(name = "Event")
public static class Event {
@Id
@GeneratedValue
private Long id;
@Convert(converter = PeriodStringConverter.class)
@Column(columnDefinition = "")
private Period span;
//Getters and setters are omitted for brevity
}
The only way to change the span
attribute is to reassign it to a different value:
Event event = entityManager.createQuery("from Event", Event.class).getSingleResult();
event.setSpan(Period
.ofYears(3)
.plusMonths(2)
.plusDays(1)
);
Mutable types
On the other hand, consider the following example where the Money
type is a mutable.
public static class Money {
private long cents;
//Getters and setters are omitted for brevity
}
@Entity(name = "Account")
public static class Account {
@Id
private Long id;
private String owner;
@Convert(converter = MoneyConverter.class)
private Money balance;
//Getters and setters are omitted for brevity
}
public static class MoneyConverter
implements AttributeConverter<Money, Long> {
@Override
public Long convertToDatabaseColumn(Money attribute) {
return attribute == null ? null : attribute.getCents();
}
@Override
public Money convertToEntityAttribute(Long dbData) {
return dbData == null ? null : new Money(dbData);
}
}
A mutable Object
allows you to modify its internal structure, and Hibernate’s dirty checking mechanism is going to propagate the change to the database:
Account account = entityManager.find(Account.class, 1L);
account.getBalance().setCents(150 * 100L);
entityManager.persist(account);
Although the For this reason, prefer immutable types over mutable ones whenever possible. |
Using the AttributeConverter entity property as a query parameter
Assuming you have the following entity:
Example 77. Photo
entity with AttributeConverter
@Entity(name = "Photo")
public static class Photo {
@Id
private Integer id;
@Column(length = 256)
private String name;
@Column(length = 256)
@Convert(converter = CaptionConverter.class)
private Caption caption;
//Getters and setters are omitted for brevity
}
And the Caption
class looks as follows:
Example 78. Caption
Java object
public static class Caption {
private String text;
public Caption(String text) {
this.text = text;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
@Override
public boolean equals(Object o) {
if ( this == o ) {
return true;
}
if ( o == null || getClass() != o.getClass() ) {
return false;
}
Caption caption = (Caption) o;
return text != null ? text.equals( caption.text ) : caption.text == null;
}
@Override
public int hashCode() {
return text != null ? text.hashCode() : 0;
}
}
And we have an AttributeConverter
to handle the Caption
Java object:
Example 79. Caption
Java object AttributeConverter
public static class CaptionConverter
implements AttributeConverter<Caption, String> {
@Override
public String convertToDatabaseColumn(Caption attribute) {
return attribute.getText();
}
@Override
public Caption convertToEntityAttribute(String dbData) {
return new Caption( dbData );
}
}
Traditionally, you could only use the DB data Caption
representation, which in our case is a String
, when referencing the caption
entity property.
Example 80. Filtering by the Caption
property using the DB data representation
Photo photo = entityManager.createQuery(
"select p " +
"from Photo p " +
"where upper(caption) = upper(:caption) ", Photo.class )
.setParameter( "caption", "Nicolae Grigorescu" )
.getSingleResult();
In order to use the Java object Caption
representation, you have to get the associated Hibernate Type
.
Example 81. Filtering by the Caption
property using the Java Object representation
SessionFactoryImplementor sessionFactory = entityManager.getEntityManagerFactory()
.unwrap( SessionFactoryImplementor.class );
final MappingMetamodelImplementor mappingMetamodel = sessionFactory
.getRuntimeMetamodels()
.getMappingMetamodel();
Type captionType = mappingMetamodel
.getEntityDescriptor( Photo.class )
.getPropertyType( "caption" );
Photo photo = (Photo) entityManager.createQuery(
"select p " +
"from Photo p " +
"where upper(caption) = upper(:caption) ", Photo.class )
.unwrap( Query.class )
.setParameter(
"caption",
new Caption( "Nicolae Grigorescu" ),
(BindableType) captionType
)
.getSingleResult();
By passing the associated Hibernate Type
, you can use the Caption
object when binding the query parameter value.
2.2.51. Registries
We’ve covered JavaTypeRegistry
and JdbcTypeRegistry
a few times now, mainly in regards to mapping resolution
as discussed in Resolving the composition. But they each also serve additional important roles.
The JavaTypeRegistry
is a registry of JavaType
references keyed by Java type. In addition to mapping resolution,
this registry is used to handle Class
references exposed in various APIs such as Query
parameter types.
JavaType
references can be registered through @JavaTypeRegistration
.
The JdbcTypeRegistry
is a registry of JdbcType
references keyed by an integer code. As discussed in
JdbcType, these type-codes typically match with the corresponding code from
java.sql.Types
, but that is not a requirement — integers other than those defined by java.sql.Types
can
be used. This might be useful for mapping JDBC User Data Types (UDTs) or other specialized database-specific
types (PostgreSQL’s UUID type, e.g.). In addition to its use in mapping resolution, this registry is also used
as the primary source for resolving «discovered» values in a JDBC ResultSet
. JdbcType
references can be
registered through @JdbcTypeRegistration
.
See TypeContributor for an alternative to @JavaTypeRegistration
and @JdbcTypeRegistration
for
registration.
2.2.52. TypeContributor
org.hibernate.boot.model.TypeContributor
is a contract for overriding or extending parts of the Hibernate type
system.
There are many ways to integrate a TypeContributor
. The most common is to define the TypeContributor
as
a Java service (see java.util.ServiceLoader
).
TypeContributor
is passed a TypeContributions
reference, which allows registration of custom JavaType
,
JdbcType
and BasicType
references.
While TypeContributor
still exposes the ability to register BasicType
references, this is considered
deprecated. As of 6.0, these BasicType
registrations are only used while interpreting hbm.xml
mappings,
which are themselves considered deprecated. Use Custom type mapping or Compositional basic mapping instead.
2.2.53. Case Study : BitSet
We’ve covered many ways to specify basic value mappings so far. This section will look at mapping the
java.util.BitSet
type by applying the different techniques covered so far.
Example 82. Implicit BitSet mapping
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
private BitSet bitSet;
//Getters and setters are omitted for brevity
}
As mentioned previously, the worst-case fallback for Hibernate mapping a basic type
which implements Serializable
is to simply serialize it to the database. BitSet
does implement Serializable
, so by default Hibernate would handle this mapping by serialization.
That is not an ideal mapping. In the following sections we will look at approaches to change
various aspects of how the BitSet gets mapped to the database.
Using AttributeConverter
We’ve seen uses of AttributeConverter
previously.
This works well in most cases and is portable across Jakarta Persistence providers.
Example 83. BitSet AttributeConverter
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
@Convert(converter = BitSetConverter.class)
private BitSet bitSet;
//Getters and setters are omitted for brevity
}
@Converter(autoApply = true)
public static class BitSetConverter implements AttributeConverter<BitSet,String> {
@Override
public String convertToDatabaseColumn(BitSet attribute) {
return BitSetHelper.bitSetToString(attribute);
}
@Override
public BitSet convertToEntityAttribute(String dbData) {
return BitSetHelper.stringToBitSet(dbData);
}
}
The See AttributeConverters for details. |
This greatly improves the reading and writing performance of dealing with these
BitSet values because the AttributeConverter
does that more efficiently using
a simple externalizable form of the BitSet rather than serializing and deserializing
the values.
See also AttributeConverter
Mutability Plan.
Using a custom JavaTypeDescriptor
As covered in [basic-mapping-explicit], we will define a JavaType
for BitSet
that maps values to VARCHAR
for storage by default.
Example 84. BitSet JavaTypeDescriptor
public class BitSetJavaType extends AbstractClassJavaType<BitSet> {
public static final BitSetJavaType INSTANCE = new BitSetJavaType();
public BitSetJavaType() {
super(BitSet.class);
}
@Override
public MutabilityPlan<BitSet> getMutabilityPlan() {
return BitSetMutabilityPlan.INSTANCE;
}
@Override
public JdbcType getRecommendedJdbcType(JdbcTypeIndicators indicators) {
return indicators.getTypeConfiguration()
.getJdbcTypeRegistry()
.getDescriptor(Types.VARCHAR);
}
@Override
public String toString(BitSet value) {
return BitSetHelper.bitSetToString(value);
}
@Override
public BitSet fromString(CharSequence string) {
return BitSetHelper.stringToBitSet(string.toString());
}
@SuppressWarnings("unchecked")
public <X> X unwrap(BitSet value, Class<X> type, WrapperOptions options) {
if (value == null) {
return null;
}
if (BitSet.class.isAssignableFrom(type)) {
return (X) value;
}
if (String.class.isAssignableFrom(type)) {
return (X) toString(value);
}
if (type.isArray()) {
if (type.getComponentType() == byte.class) {
return (X) value.toByteArray();
}
}
throw unknownUnwrap(type);
}
public <X> BitSet wrap(X value, WrapperOptions options) {
if (value == null) {
return null;
}
if (value instanceof CharSequence) {
return fromString((CharSequence) value);
}
if (value instanceof BitSet) {
return (BitSet) value;
}
throw unknownWrap(value.getClass());
}
}
We can either apply that type locally using @JavaType
Example 85. @JavaType
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
@JavaType(BitSetJavaType.class)
private BitSet bitSet;
//Constructors, getters, and setters are omitted for brevity
}
Or we can apply it globally using @JavaTypeRegistration
. This allows the registered JavaType
to be used as the default whenever we encounter the BitSet
type
Example 86. @JavaTypeRegistration
@Entity(name = "Product")
@JavaTypeRegistration(javaType = BitSet.class, descriptorClass = BitSetJavaType.class)
public static class Product {
@Id
private Integer id;
private BitSet bitSet;
//Constructors, getters, and setters are omitted for brevity
}
Selecting different JdbcTypeDescriptor
Our custom BitSetJavaType
maps BitSet
values to VARCHAR
by default. That was a better option
than direct serialization. But as BitSet
is ultimately binary data we would probably really want to
map this to VARBINARY
type instead. One way to do that would be to change BitSetJavaType#getRecommendedJdbcType
to instead return VARBINARY
descriptor. Another option would be to use a local @JdbcType
or @JdbcTypeCode
.
The following examples for specifying the JdbcType
assume our BitSetJavaType
is globally registered.
We will again store the values as VARBINARY
in the database. The difference now however is that
the coercion methods #wrap
and #unwrap
will be used to prepare the value rather than relying on
serialization.
Example 87. @JdbcTypeCode
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
@JdbcTypeCode(Types.VARBINARY)
private BitSet bitSet;
//Constructors, getters, and setters are omitted for brevity
}
In this example, @JdbcTypeCode
has been used to indicate that the JdbcType
registered for JDBC’s
VARBINARY
type should be used.
Example 88. @JdbcType
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
@JdbcType(CustomBinaryJdbcType.class)
private BitSet bitSet;
//Constructors, getters, and setters are omitted for brevity
}
In this example, @JdbcType
has been used to specify our custom BitSetJdbcType
descriptor locally for
this attribute.
We could instead replace how Hibernate deals with all VARBINARY
handling with our custom impl using
@JdbcTypeRegistration
Example 89. @JdbcType
@Entity(name = "Product")
@JdbcTypeRegistration(CustomBinaryJdbcType.class)
public static class Product {
@Id
private Integer id;
private BitSet bitSet;
//Constructors, getters, and setters are omitted for brevity
}
2.2.54. SQL quoted identifiers
You can force Hibernate to quote an identifier in the generated SQL by enclosing the table or column name in backticks in the mapping document.
While traditionally, Hibernate used backticks for escaping SQL reserved keywords, Jakarta Persistence uses double quotes instead.
Once the reserved keywords are escaped, Hibernate will use the correct quotation style for the SQL Dialect
.
This is usually double quotes, but SQL Server uses brackets and MySQL uses backticks.
Example 90. Hibernate quoting
@Entity(name = "Product")
public static class Product {
@Id
private Long id;
@Column(name = "`name`")
private String name;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
Example 91. Jakarta Persistence quoting
@Entity(name = "Product")
public static class Product {
@Id
private Long id;
@Column(name = "\"name\"")
private String name;
@Column(name = "\"number\"")
private String number;
//Getters and setters are omitted for brevity
}
Because name
and number
are reserved words, the Product
entity mapping uses backticks to quote these column names.
When saving the following Product entity
, Hibernate generates the following SQL insert statement:
Example 92. Persisting a quoted column name
Product product = new Product();
product.setId(1L);
product.setName("Mobile phone");
product.setNumber("123-456-7890");
entityManager.persist(product);
INSERT INTO Product ("name", "number", id)
VALUES ('Mobile phone', '123-456-7890', 1)
Global quoting
Hibernate can also quote all identifiers (e.g. table, columns) using the following configuration property:
<property
name="hibernate.globally_quoted_identifiers"
value="true"
/>
This way, we don’t need to manually quote any identifier:
Example 93. Jakarta Persistence quoting
@Entity(name = "Product")
public static class Product {
@Id
private Long id;
private String name;
private String number;
//Getters and setters are omitted for brevity
}
When persisting a Product
entity, Hibernate is going to quote all identifiers as in the following example:
INSERT INTO "Product" ("name", "number", "id")
VALUES ('Mobile phone', '123-456-7890', 1)
As you can see, both the table name and all the column have been quoted.
For more about quoting-related configuration properties, check out the Mapping configurations section as well.
2.2.55. Generated properties
- NOTE
-
This section talks about generating values for non-identifier attributes. For discussion of generated identifier values, see Generated identifier values.
Generated attributes have their values generated as part of performing a SQL INSERT or UPDATE. Applications can generate these
values in any number of ways (SQL DEFAULT value, trigger, etc). Typically, the application needs to refresh objects that
contain any properties for which the database was generating values, which is a major drawback.
Applications can also delegate generation to Hibernate, in which case Hibernate will manage the value generation
and (potential[3]) state refresh itself.
Only Generated attributes must additionally be non-insertable and non-updateable. |
Hibernate supports both in-VM and in-DB generation. A generation that uses the current JVM timestamp as the
generated value is an example of an in-VM strategy. A generation that uses the database’s current_timestamp
function is an example of an in-DB strategy.
Hibernate supports the following timing (when) for generation:
NEVER
(the default)-
the given attribute value is not generated
INSERT
-
the attribute value is generated on insert but is not regenerated on subsequent updates
ALWAYS
-
the attribute value is generated both on insert and update.
Hibernate supports multiple ways to mark an attribute as generated:
-
Using the dedicated generators provided by Hibernate
-
@CurrentTimestamp
—@CurrentTimestamp
-
@CreationTimestamp
—@CreationTimestamp
-
@UpdateTimestamp
—@UpdateTimestamp
annotation -
@Generated
—@Generated
annotation -
@GeneratorType
— is deprecated and not covered here -
Using a custom generation strategy — Custom generation strategy
@CurrentTimestamp
The @CurrentTimestamp
annotation is an in-DB strategy that can be configured for either INSERT or ALWAYS timing.
It uses the database’s current_timestamp
function as the generated value
Example 94. @UpdateTimestamp
mapping example
@CurrentTimestamp(event = INSERT)
public Instant createdAt;
@CurrentTimestamp(event = {INSERT, UPDATE})
public Instant lastUpdatedAt;
@CreationTimestamp
The @CreationTimestamp
annotation is an in-VM INSERT
strategy. Hibernate will use
the current timestamp of the JVM as the insert value for the attribute.
Supports most temporal types (java.time.Instant
, java.util.Date
, java.util.Calendar
, etc)
Example 95. @CreationTimestamp
mapping example
@Entity(name = "Event")
public static class Event {
@Id
@GeneratedValue
private Long id;
@Column(name = "`timestamp`")
@CreationTimestamp
private Date timestamp;
//Constructors, getters, and setters are omitted for brevity
}
While inserting the Event
, Hibernate will populate the underlying timestamp
column with the current JVM timestamp value
@UpdateTimestamp
annotation
The @UpdateTimestamp
annotation is an in-VM INSERT
strategy. Hibernate will use
the current timestamp of the JVM as the insert and update value for the attribute.
Supports most temporal types (java.time.Instant
, java.util.Date
, java.util.Calendar
, etc)
Example 96. @UpdateTimestamp
mapping example
@Entity(name = "Bid")
public static class Bid {
@Id
@GeneratedValue
private Long id;
@Column(name = "updated_on")
@UpdateTimestamp
private Date updatedOn;
@Column(name = "updated_by")
private String updatedBy;
private Long cents;
//Getters and setters are omitted for brevity
}
@Generated
annotation
The @Generated
annotation is an in-DB strategy that can be configured for either INSERT or ALWAYS timing
This is the legacy mapping for in-DB generated values.
Example 97. @Generated
mapping example
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String firstName;
private String lastName;
private String middleName1;
private String middleName2;
private String middleName3;
private String middleName4;
private String middleName5;
@Generated(event = {INSERT,UPDATE})
@Column(columnDefinition =
"AS CONCAT(" +
" COALESCE(firstName, ''), " +
" COALESCE(' ' + middleName1, ''), " +
" COALESCE(' ' + middleName2, ''), " +
" COALESCE(' ' + middleName3, ''), " +
" COALESCE(' ' + middleName4, ''), " +
" COALESCE(' ' + middleName5, ''), " +
" COALESCE(' ' + lastName, '') " +
")")
private String fullName;
}
Custom generation strategy
Hibernate also supports value generation via a pluggable API using @ValueGenerationType
and AnnotationValueGeneration
allowing users to define any generation strategy they wish.
Let’s look at an example of generating UUID values. First the attribute mapping
Example 98. Custom generation mapping example
@GeneratedUuidValue( timing = GenerationTiming.INSERT )
public UUID createdUuid;
@GeneratedUuidValue( timing = GenerationTiming.ALWAYS )
public UUID updatedUuid;
This example makes use of an annotation named @GeneratedUuidValue
— but where is that annotation defined? This is a custom
annotations provided by the application.
Example 99. Custom generation mapping example
@ValueGenerationType( generatedBy = UuidValueGeneration.class )
@Retention(RetentionPolicy.RUNTIME)
@Target( { ElementType.FIELD, ElementType.METHOD, ElementType.ANNOTATION_TYPE } )
@Inherited
public @interface GeneratedUuidValue {
GenerationTiming timing();
}
The @ValueGenerationType( generatedBy = UuidValueGeneration.class )
here is the important piece; it tells
Hibernate how to generate values for the attribute — here it will use the specified UuidValueGeneration
class
Example 100. Custom generation mapping example
public static class UuidValueGeneration implements BeforeExecutionGenerator {
private final EnumSet<EventType> eventTypes;
public UuidValueGeneration(GeneratedUuidValue annotation) {
eventTypes = annotation.timing().getEquivalent().eventTypes();
}
@Override
public EnumSet<EventType> getEventTypes() {
return eventTypes;
}
@Override
public Object generate(SharedSessionContractImplementor session, Object owner, Object currentValue, EventType eventType) {
return SafeRandomUUIDGenerator.safeRandomUUID();
}
}
2.2.56. Column transformers: read and write expressions
Hibernate allows you to customize the SQL it uses to read and write the values of columns mapped to @Basic
types.
For example, if your database provides a set of data encryption functions, you can invoke them for individual columns like in the following example.
Example 101. @ColumnTransformer
example
@Entity(name = "Employee")
public static class Employee {
@Id
private Long id;
@NaturalId
private String username;
@Column(name = "pswd")
@ColumnTransformer(
read = "decrypt('AES', '00', pswd )",
write = "encrypt('AES', '00', ?)"
)
// For H2 2.0.202+ one must use the varbinary DDL type
// @Column(name = "pswd", columnDefinition = "varbinary")
// @ColumnTransformer(
// read = "trim(trailing u&'\\0000' from cast(decrypt('AES', '00', pswd ) as character varying))",
// write = "encrypt('AES', '00', ?)"
// )
private String password;
private int accessLevel;
@ManyToOne(fetch = FetchType.LAZY)
private Department department;
@ManyToMany(mappedBy = "employees")
private List<Project> projects = new ArrayList<>();
//Getters and setters omitted for brevity
}
If a property uses more than one column, you must use the forColumn
attribute to specify which column the @ColumnTransformer
read and write expressions are targeting.
Example 102. @ColumnTransformer
forColumn
attribute usage
@Entity(name = "Savings")
public static class Savings {
@Id
private Long id;
@CompositeType(MonetaryAmountUserType.class)
@AttributeOverrides({
@AttributeOverride(name = "amount", column = @Column(name = "money")),
@AttributeOverride(name = "currency", column = @Column(name = "currency"))
})
@ColumnTransformer(
forColumn = "money",
read = "money / 100",
write = "? * 100"
)
private MonetaryAmount wallet;
//Getters and setters omitted for brevity
}
Hibernate applies the custom expressions automatically whenever the property is referenced in a query.
This functionality is similar to a derived-property @Formula with two differences:
-
The property is backed by one or more columns that are exported as part of automatic schema generation.
-
The property is read-write, not read-only.
The write
expression, if specified, must contain exactly one ‘?’ placeholder for the value.
Example 103. Persisting an entity with a @ColumnTransformer
and a composite type
doInJPA(this::entityManagerFactory, entityManager -> {
Savings savings = new Savings();
savings.setId(1L);
savings.setWallet(new MonetaryAmount(BigDecimal.TEN, Currency.getInstance(Locale.US)));
entityManager.persist(savings);
});
doInJPA(this::entityManagerFactory, entityManager -> {
Savings savings = entityManager.find(Savings.class, 1L);
assertEquals(10, savings.getWallet().getAmount().intValue());
assertEquals(Currency.getInstance(Locale.US), savings.getWallet().getCurrency());
});
INSERT INTO Savings (money, currency, id)
VALUES (10 * 100, 'USD', 1)
SELECT
s.id as id1_0_0_,
s.money / 100 as money2_0_0_,
s.currency as currency3_0_0_
FROM
Savings s
WHERE
s.id = 1
2.3. Embeddable values
Historically Hibernate called these components.
Jakarta Persistence calls them embeddables.
Either way, the concept is the same: a composition of values.
For example, we might have a Publisher
class that is a composition of name
and country
,
or a Location
class that is a composition of country
and city
.
Usage of the word embeddable To avoid any confusion with the annotation that marks a given embeddable type, the annotation will be further referred to as Throughout this chapter and thereafter, for brevity sake, embeddable types may also be referred to as embeddable. |
Example 104. Embeddable type example
@Embeddable
public static class Publisher {
private String name;
private Location location;
public Publisher(String name, Location location) {
this.name = name;
this.location = location;
}
private Publisher() {}
//Getters and setters are omitted for brevity
}
@Embeddable
public static class Location {
private String country;
private String city;
public Location(String country, String city) {
this.country = country;
this.city = city;
}
private Location() {}
//Getters and setters are omitted for brevity
}
An embeddable type is another form of a value type, and its lifecycle is bound to a parent entity type, therefore inheriting the attribute access from its parent (for details on attribute access, see Access strategies).
Embeddable types can be made up of basic values as well as associations, with the caveat that, when used as collection elements, they cannot define collections themselves.
2.3.1. Component / Embedded
Most often, embeddable types are used to group multiple basic type mappings and reuse them across several entities.
Example 105. Simple Embeddable
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
private Publisher publisher;
//Getters and setters are omitted for brevity
}
@Embeddable
public static class Publisher {
@Column(name = "publisher_name")
private String name;
@Column(name = "publisher_country")
private String country;
//Getters and setters, equals and hashCode methods omitted for brevity
}
create table Book (
id bigint not null,
author varchar(255),
publisher_country varchar(255),
publisher_name varchar(255),
title varchar(255),
primary key (id)
)
Jakarta Persistence defines two terms for working with an embeddable type:
|
So, the embeddable type is represented by the Publisher
class and
the parent entity makes use of it through the book#publisher
object composition.
The composed values are mapped to the same table as the parent table.
Composition is part of good object-oriented data modeling (idiomatic Java).
In fact, that table could also be mapped by the following entity type instead.
Example 106. Alternative to embeddable type composition
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
@Column(name = "publisher_name")
private String publisherName;
@Column(name = "publisher_country")
private String publisherCountry;
//Getters and setters are omitted for brevity
}
The composition form is certainly more object-oriented, and that becomes more evident as we work with multiple embeddable types.
2.3.2. Overriding Embeddable types
Although from an object-oriented perspective, it’s much more convenient to work with embeddable types, when we reuse the same
embeddable multiple times on the same class, the Jakarta Persistence specification requires to set the associated column names explicitly.
This requirement is due to how object properties are mapped to database columns.
By default, Jakarta Persistence expects a database column having the same name with its associated object property.
When including multiple embeddables, the implicit name-based mapping rule doesn’t work anymore because multiple object
properties could end-up being mapped to the same database column.
When an embeddable type is used multiple times, Jakarta Persistence defines the @AttributeOverride
and @AssociationOverride
annotations to handle this scenario to override the default column names defined
by the Embeddable.
See Embeddables and ImplicitNamingStrategy for an alternative to using @AttributeOverride and @AssociationOverride
|
Considering you have the following Publisher
embeddable type
which defines a @ManyToOne
association with the Country
entity:
Example 107. Embeddable type with a @ManyToOne
association
@Embeddable
public static class Publisher {
private String name;
@ManyToOne(fetch = FetchType.LAZY)
private Country country;
//Getters and setters, equals and hashCode methods omitted for brevity
}
@Entity(name = "Country")
public static class Country {
@Id
@GeneratedValue
private Long id;
@NaturalId
private String name;
//Getters and setters are omitted for brevity
}
create table Country (
id bigint not null,
name varchar(255),
primary key (id)
)
alter table Country
add constraint UK_p1n05aafu73sbm3ggsxqeditd
unique (name)
Now, if you have a Book
entity which declares two Publisher
embeddable types for the ebook and paperback versions,
you cannot use the default Publisher
embeddable mapping since there will be a conflict between the two embeddable column mappings.
Therefore, the Book
entity needs to override the embeddable type mappings for each Publisher
attribute:
Example 108. Overriding embeddable type attributes
@Entity(name = "Book")
@AttributeOverrides({
@AttributeOverride(
name = "ebookPublisher.name",
column = @Column(name = "ebook_pub_name")
),
@AttributeOverride(
name = "paperBackPublisher.name",
column = @Column(name = "paper_back_pub_name")
)
})
@AssociationOverrides({
@AssociationOverride(
name = "ebookPublisher.country",
joinColumns = @JoinColumn(name = "ebook_pub_country_id")
),
@AssociationOverride(
name = "paperBackPublisher.country",
joinColumns = @JoinColumn(name = "paper_back_pub_country_id")
)
})
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
private Publisher ebookPublisher;
private Publisher paperBackPublisher;
//Getters and setters are omitted for brevity
}
create table Book (
id bigint not null,
author varchar(255),
ebook_pub_name varchar(255),
paper_back_pub_name varchar(255),
title varchar(255),
ebook_pub_country_id bigint,
paper_back_pub_country_id bigint,
primary key (id)
)
alter table Book
add constraint FKm39ibh5jstybnslaoojkbac2g
foreign key (ebook_pub_country_id)
references Country
alter table Book
add constraint FK7kqy9da323p7jw7wvqgs6aek7
foreign key (paper_back_pub_country_id)
references Country
2.3.3. Collections of embeddable types
Collections of embeddable types are specifically valued collections (as embeddable types are value types).
Value collections are covered in detail in Collections of value types.
2.3.4. Embeddable type as a Map key
Embeddable types can also be used as Map
keys.
This topic is converted in detail in Map — key.
2.3.5. Embeddable type as identifier
Embeddable types can also be used as entity type identifiers.
This usage is covered in detail in Composite identifiers.
Embeddable types that are used as collection entries, map keys or entity type identifiers cannot include their own collection mappings. |
2.3.6. @Target
mapping
The @Target
annotation is used to specify the implementation class of a given association that is mapped via an interface.
The
@ManyToOne
,
@OneToOne
,
@OneToMany
, and
@ManyToMany
feature a targetEntity
attribute to specify the actual class of the entity association when an interface is used for the mapping.
However, for simple embeddable types, there is no such construct and so you need to use the Hibernate-specific @Target
annotation instead.
Example 109. @Target
mapping usage
public interface Coordinates {
double x();
double y();
}
@Embeddable
public static class GPS implements Coordinates {
private double latitude;
private double longitude;
private GPS() {
}
public GPS(double latitude, double longitude) {
this.latitude = latitude;
this.longitude = longitude;
}
@Override
public double x() {
return latitude;
}
@Override
public double y() {
return longitude;
}
}
@Entity(name = "City")
public static class City {
@Id
@GeneratedValue
private Long id;
private String name;
@Embedded
@Target(GPS.class)
private Coordinates coordinates;
//Getters and setters omitted for brevity
}
The coordinates
embeddable type is mapped as the Coordinates
interface.
However, Hibernate needs to know the actual implementation type, which is GPS
in this case,
hence the @Target
annotation is used to provide this information.
Assuming we have persisted the following City
entity:
Example 110. @Target
persist example
doInJPA(this::entityManagerFactory, entityManager -> {
City cluj = new City();
cluj.setName("Cluj");
cluj.setCoordinates(new GPS(46.77120, 23.62360));
entityManager.persist(cluj);
});
When fetching the City
entity, the coordinates
property is mapped by the @Target
expression:
Example 111. @Target
fetching example
doInJPA(this::entityManagerFactory, entityManager -> {
City cluj = entityManager.find(City.class, 1L);
assertEquals(46.77120, cluj.getCoordinates().x(), 0.00001);
assertEquals(23.62360, cluj.getCoordinates().y(), 0.00001);
});
SELECT
c.id as id1_0_0_,
c.latitude as latitude2_0_0_,
c.longitude as longitud3_0_0_,
c.name as name4_0_0_
FROM
City c
WHERE
c.id = ?
-- binding parameter [1] as [BIGINT] - [1]
-- extracted value ([latitude2_0_0_] : [DOUBLE]) - [46.7712]
-- extracted value ([longitud3_0_0_] : [DOUBLE]) - [23.6236]
-- extracted value ([name4_0_0_] : [VARCHAR]) - [Cluj]
Therefore, the @Target
annotation is used to define a custom join association between the parent-child association.
2.3.7. @Parent
mapping
The Hibernate-specific @Parent
annotation allows you to reference the owner entity from within an embeddable.
Example 112. @Parent
mapping usage
@Embeddable
public static class GPS {
private double latitude;
private double longitude;
@Parent
private City city;
//Getters and setters omitted for brevity
}
@Entity(name = "City")
public static class City {
@Id
@GeneratedValue
private Long id;
private String name;
@Embedded
@Target(GPS.class)
private GPS coordinates;
//Getters and setters omitted for brevity
}
Assuming we have persisted the following City
entity:
Example 113. @Parent
persist example
doInJPA(this::entityManagerFactory, entityManager -> {
City cluj = new City();
cluj.setName("Cluj");
cluj.setCoordinates(new GPS(46.77120, 23.62360));
entityManager.persist(cluj);
});
When fetching the City
entity, the city
property of the embeddable type acts as a back reference to the owning parent entity:
Example 114. @Parent
fetching example
doInJPA(this::entityManagerFactory, entityManager -> {
City cluj = entityManager.find(City.class, 1L);
assertSame(cluj, cluj.getCoordinates().getCity());
});
Therefore, the @Parent
annotation is used to define the association between an embeddable type and the owning entity.
2.3.8. Custom instantiation
Jakarta Persistence requires embeddable classes to follow Java Bean conventions. Part of this is the
definition of a non-arg constructor. However, not all value compositions applications might map as embeddable
values follow Java Bean conventions — e.g. a struct or Java 15 record.
Hibernate allows the use of a custom instantiator for creating the embeddable instances through the
org.hibernate.metamodel.spi.EmbeddableInstantiator
contract. For example, consider the following
embeddable:
Example 115. EmbeddableInstantiator
— Embeddable
@Embeddable
public class Name {
@Column(name = "first_name")
private final String first;
@Column(name = "last_name")
private final String last;
private Name() {
throw new UnsupportedOperationException();
}
public Name(String first, String last) {
this.first = first;
this.last = last;
}
public String getFirstName() {
return first;
}
public String getLastName() {
return last;
}
}
Here, Name
only allows use of the constructor accepting its state. Because this class does not follow Java Bean
conventions, in terms of constructor, a custom strategy for instantiation is needed.
Example 116. EmbeddableInstantiator
— Implementation
public class NameInstantiator implements EmbeddableInstantiator {
@Override
public Object instantiate(ValueAccess valueAccess, SessionFactoryImplementor sessionFactory) {
// alphabetical
final String first = valueAccess.getValue( 0, String.class );
final String last = valueAccess.getValue( 1, String.class );
return new Name( first, last );
}
// ...
}
There are a few ways to specify the custom instantiator. The @org.hibernate.annotations.EmbeddableInstantiator
annotation can be used on the embedded attribute:
Example 117. @EmbeddableInstantiator
on attribute
@Entity
public class Person {
@Id
public Integer id;
@Embedded
@EmbeddableInstantiator( NameInstantiator.class )
public Name name;
@ElementCollection
@Embedded
@EmbeddableInstantiator( NameInstantiator.class )
public Set<Name> aliases;
}
@EmbeddableInstantiator
may also be specified on the embeddable class:
Example 118. @EmbeddableInstantiator
on class
@Embeddable
@EmbeddableInstantiator( NameInstantiator.class )
public class Name {
@Column(name = "first_name")
private final String first;
@Column(name = "last_name")
private final String last;
private Name() {
throw new UnsupportedOperationException();
}
public Name(String first, String last) {
this.first = first;
this.last = last;
}
public String getFirstName() {
return first;
}
public String getLastName() {
return last;
}
}
@Entity
public class Person {
@Id
public Integer id;
@Embedded
public Name name;
@ElementCollection
@Embedded
public Set<Name> aliases;
}
Lastly, @org.hibernate.annotations.EmbeddableInstantiatorRegistration
may be used, which is useful
when the application developer does not control the embeddable to be able to apply the instantiator
on the embeddable.
Example 119. @EmbeddableInstantiatorRegistration
@Entity
@EmbeddableInstantiatorRegistration( embeddableClass = Name.class, instantiator = NameInstantiator.class )
public class Person {
@Id
public Integer id;
@Embedded
public Name name;
@ElementCollection
@Embedded
public Set<Name> aliases;
}
2.3.9. Custom type mapping
Another approach is to supply the implementation of the org.hibernate.usertype.CompositeUserType
contract using @CompositeType
,
which is an extension to the org.hibernate.metamodel.spi.EmbeddableInstantiator
contract.
There are also corresponding, specialized forms of @CompositeType
for specific model parts:
-
When mapping a Map,
@CompositeType
describes the Map value while@MapKeyCompositeType
describes the Map key -
For collection mappings,
@CompositeType
describes the elements
For example, consider the following custom type:
Example 120. CompositeUserType
— Domain type
public class Name {
private final String first;
private final String last;
public Name(String first, String last) {
this.first = first;
this.last = last;
}
public String firstName() {
return first;
}
public String lastName() {
return last;
}
}
Here, Name
only allows use of the constructor accepting its state. Because this class does not follow Java Bean
conventions, a custom user type for instantiation and state access is needed.
Example 121. CompositeUserType
— Implementation
public class NameCompositeUserType implements CompositeUserType<Name> {
public static class NameMapper {
String firstName;
String lastName;
}
@Override
public Class<?> embeddable() {
return NameMapper.class;
}
@Override
public Class<Name> returnedClass() {
return Name.class;
}
@Override
public Name instantiate(ValueAccess valueAccess, SessionFactoryImplementor sessionFactory) {
// alphabetical
final String first = valueAccess.getValue( 0, String.class );
final String last = valueAccess.getValue( 1, String.class );
return new Name( first, last );
}
@Override
public Object getPropertyValue(Name component, int property) throws HibernateException {
// alphabetical
switch ( property ) {
case 0:
return component.firstName();
case 1:
return component.lastName();
}
return null;
}
@Override
public boolean equals(Name x, Name y) {
return x == y || x != null && Objects.equals( x.firstName(), y.firstName() )
&& Objects.equals( x.lastName(), y.lastName() );
}
@Override
public int hashCode(Name x) {
return Objects.hash( x.firstName(), x.lastName() );
}
@Override
public Name deepCopy(Name value) {
return value; // immutable
}
@Override
public boolean isMutable() {
return false;
}
@Override
public Serializable disassemble(Name value) {
return new String[] { value.firstName(), value.lastName() };
}
@Override
public Name assemble(Serializable cached, Object owner) {
final String[] parts = (String[]) cached;
return new Name( parts[0], parts[1] );
}
@Override
public Name replace(Name detached, Name managed, Object owner) {
return detached;
}
}
A composite user type needs an embeddable mapper class, which represents the embeddable mapping structure of the type
i.e. the way the type would look like if you had the option to write a custom @Embeddable
class.
In addition to the instantiation logic, a composite user type also has to provide a way to decompose the returned type
into the individual components/properties of the embeddable mapper class through getPropertyValue
.
The property index, just like in the instantiate
method, is based on the alphabetical order of the attribute names
of the embeddable mapper class.
The composite user type also needs to provide methods to handle the mutability, equals, hashCode and the cache
serialization and deserialization of the returned type.
There are a few ways to specify the composite user type. The @org.hibernate.annotations.CompositeType
annotation can be used on the embedded and element collection attributes:
Example 122. @CompositeType
on attribute
@Entity
public class Person {
@Id
public Integer id;
@Embedded
@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
@CompositeType( NameCompositeUserType.class )
public Name name;
@ElementCollection
@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
@CompositeType( NameCompositeUserType.class )
public Set<Name> aliases;
}
Or @org.hibernate.annotations.CompositeTypeRegistration
may be used, which is useful
when the application developer wants to apply the composite user type for all domain type uses.
Example 123. @CompositeTypeRegistration
@Entity
@CompositeTypeRegistration( embeddableClass = Name.class, userType = NameCompositeUserType.class )
public class Person {
@Id
public Integer id;
@Embedded
@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
public Name name;
@ElementCollection
@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
public Set<Name> aliases;
}
2.3.10. Embeddables and ImplicitNamingStrategy
The |
Hibernate naming strategies are covered in detail in Naming.
However, for the purposes of this discussion, Hibernate has the capability to interpret implicit column names in a way that is safe for use with multiple embeddable types.
Example 124. Implicit multiple embeddable type mapping
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
private Publisher ebookPublisher;
private Publisher paperBackPublisher;
//Getters and setters are omitted for brevity
}
@Embeddable
public static class Publisher {
private String name;
@ManyToOne(fetch = FetchType.LAZY)
private Country country;
//Getters and setters, equals and hashCode methods omitted for brevity
}
@Entity(name = "Country")
public static class Country {
@Id
@GeneratedValue
private Long id;
@NaturalId
private String name;
//Getters and setters are omitted for brevity
}
To make it work, you need to use the ImplicitNamingStrategyComponentPathImpl
naming strategy.
Example 125. Enabling implicit embeddable type mapping using the component path naming strategy
metadataBuilder.applyImplicitNamingStrategy(
ImplicitNamingStrategyComponentPathImpl.INSTANCE
);
Now the «path» to attributes are used in the implicit column naming:
create table Book (
id bigint not null,
author varchar(255),
ebookPublisher_name varchar(255),
paperBackPublisher_name varchar(255),
title varchar(255),
ebookPublisher_country_id bigint,
paperBackPublisher_country_id bigint,
primary key (id)
)
You could even develop your own naming strategy to do other types of implicit naming strategies.
2.3.11. Aggregate embeddable mapping
An embeddable mapping is usually just a way to encapsulate columns of a table into a Java type,
but as of Hibernate 6.2, it is also possible to map embeddable types as SQL aggregate types.
Currently, there are three possible SQL aggregate types which can be specified by annotating one of the following
annotations on a persistent attribute:
-
@Struct
— maps to a named SQL object type -
@JdbcTypeCode(SqlTypes.JSON)
— maps to the SQL type JSON -
@JdbcTypeCode(SqlTypes.SQLXML)
— maps to the SQL type XML
Any read or assignment (in an update statement) expression for an attribute of such an embeddable
will resolve to the proper SQL expression to access/update the attribute of the SQL type.
Since object, JSON and XML types are not supported equally on all databases, beware that not every mapping will work on all databases.
The following table outlines the current support for the different aggregate types:
Database | Struct | JSON | XML |
---|---|---|---|
PostgreSQL |
Yes |
Yes |
No (not yet) |
Oracle |
Yes |
Yes |
No (not yet) |
DB2 |
Yes |
No (not yet) |
No (not yet) |
SQL Server |
No (not yet) |
No (not yet) |
No (not yet) |
Also note that embeddable types that are used in aggregate mappings do not yet support all kinds of attribute mappings, most notably:
-
Association mappings (
@ManyToOne
,@OneToOne
,@OneToMany
,@ManyToMany
,@ElementCollection
) -
Basic array mappings
@Struct
aggregate embeddable mapping
The @Struct
annotation can be placed on either the persistent attribute, or the embeddable type,
and requires the specification of a name i.e. the name of the SQL object type that it maps to.
The following example mapping, maps the EmbeddableAggregate
type to the SQL object type structType
:
Example 126. Mapping embeddable as SQL object type on persistent attribute level
@Entity(name = "StructHolder")
public static class StructHolder {
@Id
private Long id;
@Struct(name = "structType")
private EmbeddableAggregate aggregate;
}
The schema generation will by default emit DDL for that object type, which looks something along the lines of
create type structType as (
...
)
create table StructHolder as (
id bigint not null primary key,
aggregate structType
)
The name and the nullability of the column can be refined through applying a @Column
on the persistent attribute.
One very important thing to note is that the order of columns in the DDL definition of a type must match the order that Hibernate expects.
By default, the order of columns is based on the alphabetical ordering of the embeddable type attribute names.
Consider the following class:
@Embeddable
@Struct(name = "myStruct")
public class MyStruct {
@Column(name = "b")
String attr1;
@Column(name = "a")
String attr2;
}
The expected ordering of columns will be (b,a)
, because the name attr1
comes before attr2
in alphabetical ordering.
This example aims at showing the importance of the persistent attribute name.
Defining the embeddable type as Java record instead of a class can force a particular ordering through the definition of canonical constructor.
@Embeddable
@Struct(name = "myStruct")
public record MyStruct (
@Column(name = "a")
String attr2,
@Column(name = "b")
String attr1
) {}
In this particular example, the expected ordering of columns will be (a,b)
, because the canonical constructor of the record
defines a specific ordering of persistent attributes, which Hibernate makes use of for @Struct
mappings.
It is not necessary to switch to Java records to configure the order though.
The @Struct
annotation allows specifying the order through the attributes
member,
an array of attribute names that the embeddable type declares, which defines the order in columns appear in the SQL object type.
The same ordering as with the Java record can be achieved this way:
@Embeddable
@Struct(name = "myStruct", attributes = {"attr2", "attr1"})
public class MyStruct {
@Column(name = "b")
String attr1;
@Column(name = "a")
String attr2;
}
JSON/XML aggregate embeddable mapping
The @JdbcTypeCode
annotation for JSON and XML mappings can only be placed on the persistent attribute.
The following example mapping, maps the EmbeddableAggregate
type to the JSON SQL type:
Example 127. Mapping embeddable as JSON
@Entity(name = "JsonHolder")
public static class JsonHolder {
@Id
private Long id;
@JdbcTypeCode(SqlTypes.JSON)
private EmbeddableAggregate aggregate;
}
The schema generation will by default emit DDL that ensures the constraints of the embeddable type are respected, which looks something along the lines of
create table JsonHolder as (
id bigint not null primary key,
aggregate json,
check (json_value(aggregate, '$.attribute1') is not null)
)
Again, the name and the nullability of the aggregate
column can be refined through applying a @Column
on the persistent attribute.
2.4. Entity types
Usage of the word entity The entity type describes the mapping between the actual persistable domain model object and a database table row. Throughout this chapter and thereafter, entity types will be simply referred to as entity. |
2.4.1. POJO Models
Section 2.1 The Entity Class of the Java Persistence 2.1 specification defines its requirements for an entity class.
Applications that wish to remain portable across Jakarta Persistence providers should adhere to these requirements:
-
The entity class must be annotated with the
jakarta.persistence.Entity
annotation (or be denoted as such in XML mapping). -
The entity class must have a public or protected no-argument constructor. It may define additional constructors as well.
-
The entity class must be a top-level class.
-
An enum or interface may not be designated as an entity.
-
The entity class must not be final. No methods or persistent instance variables of the entity class may be final.
-
If an entity instance is to be used remotely as a detached object, the entity class must implement the
Serializable
interface. -
Both abstract and concrete classes can be entities. Entities may extend non-entity classes as well as entity classes, and non-entity classes may extend entity classes.
-
The persistent state of an entity is represented by instance variables, which may correspond to JavaBean-style properties.
An instance variable must be directly accessed only from within the methods of the entity by the entity instance itself.
The state of the entity is available to clients only through the entity’s accessor methods (getter/setter methods) or other business methods.
Hibernate, however, is not as strict in its requirements. The differences from the list above include:
-
The entity class must have a no-argument constructor, which may be public, protected or package visibility. It may define additional constructors as well.
-
The entity class need not be a top-level class.
-
Technically Hibernate can persist final classes or classes with final persistent state accessor (getter/setter) methods.
However, it is generally not a good idea as doing so will stop Hibernate from being able to generate proxies for lazy-loading the entity. -
Hibernate does not restrict the application developer from exposing instance variables and referencing them from outside the entity class itself.
The validity of such a paradigm, however, is debatable at best.
Let’s look at each requirement in detail.
2.4.2. Prefer non-final classes
A central feature of Hibernate is the ability to load lazily certain entity instance variables (attributes) via runtime proxies.
This feature depends upon the entity class being non-final or else implementing an interface that declares all the attribute getters/setters.
You can still persist final classes that do not implement such an interface with Hibernate,
but you will not be able to use proxies for fetching lazy associations, therefore limiting your options for performance tuning.
For the very same reason, you should also avoid declaring persistent attribute getters and setters as final.
Starting with 5.0, Hibernate offers a more robust version of bytecode enhancement as another means for handling lazy loading. |
2.4.3. Implement a no-argument constructor
The entity class should have a no-argument constructor. Both Hibernate and Jakarta Persistence require this.
Jakarta Persistence requires that this constructor be defined as public or protected.
Hibernate, for the most part, does not care about the constructor visibility, as long as the system SecurityManager allows overriding the visibility setting.
That said, the constructor should be defined with at least package visibility if you wish to leverage runtime proxy generation.
2.4.4. Declare getters and setters for persistent attributes
The Jakarta Persistence specification requires this, otherwise, the model would prevent accessing the entity persistent state fields directly from outside the entity itself.
Although Hibernate does not require it, it is recommended to follow the JavaBean conventions and define getters and setters for entity persistent attributes.
Nevertheless, you can still tell Hibernate to directly access the entity fields.
Attributes (whether fields or getters/setters) need not be declared public.
Hibernate can deal with attributes declared with the public, protected, package or private visibility.
Again, if wanting to use runtime proxy generation for lazy loading, the getter/setter should grant access to at least package visibility.
2.4.5. Providing identifier attribute(s)
Historically, providing identifier attributes was considered optional. However, not defining identifier attributes on the entity should be considered a deprecated feature that will be removed in an upcoming release. |
The identifier attribute does not necessarily need to be mapped to the column(s) that physically define the primary key.
However, it should map to column(s) that can uniquely identify each row.
We recommend that you declare consistently-named identifier attributes on persistent classes and that you use a wrapper (i.e., non-primitive) type (e.g. |
The placement of the @Id
annotation marks the persistence state access strategy.
Example 128. Identifier mapping
Hibernate offers multiple identifier generation strategies, see the Identifier Generators chapter for more about this topic.
2.4.6. Mapping the entity
The @Entity
annotation defines just the name
attribute which is used to give a specific entity name for use in JPQL queries.
By default, if the name attribute of the @Entity
annotation is missing, the unqualified name of the entity class itself will be used as the entity name.
Because the entity name is given by the unqualified name of the class, Hibernate does not allow registering multiple entities with the same name even if the entity classes reside in different packages. Without imposing this restriction, Hibernate would not know which entity class is referenced in a JPQL query if the unqualified entity name is associated with more then one entity classes. |
In the following example, the entity name (e.g. Book
) is given by the unqualified name of the entity class name.
Example 129. @Entity
mapping with an implicit name
@Entity
public class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
However, the entity name can also be set explicitly as illustrated by the following example.
Example 130. @Entity
mapping with an explicit name
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
An entity models a database table.
The identifier uniquely identifies each row in that table.
By default, the name of the table is assumed to be the same as the name of the entity.
To explicitly give the name of the table or to specify other information about the table, we would use the jakarta.persistence.Table
annotation.
Example 131. Simple @Entity
with @Table
@Entity(name = "Book")
@Table(
catalog = "public",
schema = "store",
name = "book"
)
public static class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
Mapping the catalog of the associated table
Without specifying the catalog of the associated database table a given entity is mapped to, Hibernate will use the default catalog associated with the current database connection.
However, if your database hosts multiple catalogs, you can specify the catalog where a given table is located using the catalog
attribute of the Jakarta Persistence @Table
annotation.
Let’s assume we are using MySQL and want to map a Book
entity to the book
table located in the public
catalog
which looks as follows.
Example 132. The book
table located in the public
catalog
create table public.book (
id bigint not null,
author varchar(255),
title varchar(255),
primary key (id)
) engine=InnoDB
Now, to map the Book
entity to the book
table in the public
catalog we can use the catalog
attribute of the @Table
Jakarta Persistence annotation.
Example 133. Specifying the database catalog using the @Table
annotation
@Entity(name = "Book")
@Table(
catalog = "public",
name = "book"
)
public static class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
Mapping the schema of the associated table
Without specifying the schema of the associated database table a given entity is mapped to, Hibernate will use the default schema associated with the current database connection.
However, if your database supports schemas, you can specify the schema where a given table is located using the schema
attribute of the Jakarta Persistence @Table
annotation.
Let’s assume we are using PostgreSQL and want to map a Book
entity to the book
table located in the library
schema
which looks as follows.
Example 134. The book
table located in the library
schema
create table library.book (
id int8 not null,
author varchar(255),
title varchar(255),
primary key (id)
)
Now, to map the Book
entity to the book
table in the library
schema we can use the schema
attribute of the @Table
Jakarta Persistence annotation.
Example 135. Specifying the database schema using the @Table
annotation
@Entity(name = "Book")
@Table(
schema = "library",
name = "book"
)
public static class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
The Therefore, if you’re using MySQL or MariaDB, which do not support schemas natively (schemas being just an alias for catalog), you need to use the |
2.4.7. Implementing equals()
and hashCode()
Much of the discussion in this section deals with the relation of an entity to a Hibernate Session, whether the entity is managed, transient or detached. |
Whether to implement equals()
and hashCode()
methods in your domain model, let alone how to implement them, is a surprisingly tricky discussion when it comes to ORM.
There is really just one absolute case: a class that acts as an identifier must implement equals/hashCode based on the id value(s).
Generally, this is pertinent for user-defined classes used as composite identifiers.
Beyond this one very specific use case and few others we will discuss below, you may want to consider not implementing equals/hashCode altogether.
So what’s all the fuss? Normally, most Java objects provide a built-in equals()
and hashCode()
based on the object’s identity, so each new object will be different from all others.
This is generally what you want in ordinary Java programming.
Conceptually, however, this starts to break down when you start to think about the possibility of multiple instances of a class representing the same data.
This is, in fact, exactly the case when dealing with data coming from a database.
Every time we load a specific Person
from the database we would naturally get a unique instance.
Hibernate, however, works hard to make sure that does not happen within a given Session
.
In fact, Hibernate guarantees equivalence of persistent identity (database row) and Java identity inside a particular session scope.
So if we ask a Hibernate Session
to load that specific Person multiple times we will actually get back the same instance:
Example 136. Scope of identity
Book book1 = entityManager.find(Book.class, 1L);
Book book2 = entityManager.find(Book.class, 1L);
assertTrue(book1 == book2);
Consider we have a Library
parent entity which contains a java.util.Set
of Book
entities:
Example 137. Library entity mapping
@Entity(name = "Library")
public static class Library {
@Id
private Long id;
private String name;
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "book_id")
private Set<Book> books = new HashSet<>();
//Getters and setters are omitted for brevity
}
Example 138. Set usage with Session-scoped identity
Library library = entityManager.find(Library.class, 1L);
Book book1 = entityManager.find(Book.class, 1L);
Book book2 = entityManager.find(Book.class, 1L);
library.getBooks().add(book1);
library.getBooks().add(book2);
assertEquals(1, library.getBooks().size());
However, the semantic changes when we mix instances loaded from different Sessions:
Example 139. Mixed Sessions
Book book1 = doInJPA(this::entityManagerFactory, entityManager -> {
return entityManager.find(Book.class, 1L);
});
Book book2 = doInJPA(this::entityManagerFactory, entityManager -> {
return entityManager.find(Book.class, 1L);
});
assertFalse(book1 == book2);
doInJPA(this::entityManagerFactory, entityManager -> {
Set<Book> books = new HashSet<>();
books.add(book1);
books.add(book2);
assertEquals(2, books.size());
});
Specifically, the outcome in this last example will depend on whether the Book
class
implemented equals/hashCode, and, if so, how.
If the Book
class did not override the default equals/hashCode,
then the two Book
object references are not going to be equal since their references are different.
Consider yet another case:
Example 140. Sets with transient entities
Library library = entityManager.find(Library.class, 1L);
Book book1 = new Book();
book1.setId(100L);
book1.setTitle("High-Performance Java Persistence");
Book book2 = new Book();
book2.setId(101L);
book2.setTitle("Java Persistence with Hibernate");
library.getBooks().add(book1);
library.getBooks().add(book2);
assertEquals(2, library.getBooks().size());
In cases where you will be dealing with entities outside of a Session (whether they be transient or detached),
especially in cases where you will be using them in Java collections,
you should consider implementing equals/hashCode.
A common initial approach is to use the entity’s identifier attribute as the basis for equals/hashCode calculations:
Example 141. Naive equals/hashCode implementation
@Entity(name = "Library")
public static class Library {
@Id
private Long id;
private String name;
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "book_id")
private Set<Book> books = new HashSet<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Book book = (Book) o;
return Objects.equals(id, book.id);
}
@Override
public int hashCode() {
return Objects.hash(id);
}
}
It turns out that this still breaks when adding transient instance of Book
to a set as we saw in the last example:
Example 142. Auto-generated identifiers with Sets and naive equals/hashCode
Book book1 = new Book();
book1.setTitle("High-Performance Java Persistence");
Book book2 = new Book();
book2.setTitle("Java Persistence with Hibernate");
Library library = doInJPA(this::entityManagerFactory, entityManager -> {
Library _library = entityManager.find(Library.class, 1L);
_library.getBooks().add(book1);
_library.getBooks().add(book2);
return _library;
});
assertFalse(library.getBooks().contains(book1));
assertFalse(library.getBooks().contains(book2));
The issue here is a conflict between the use of the generated identifier, the contract of Set
, and the equals/hashCode implementations.
Set
says that the equals/hashCode value for an object should not change while the object is part of the Set
.
But that is exactly what happened here because the equals/hasCode are based on the (generated) id, which was not set until the Jakarta Persistence transaction is committed.
Note that this is just a concern when using generated identifiers.
If you are using assigned identifiers this will not be a problem, assuming the identifier value is assigned prior to adding to the Set
.
Another option is to force the identifier to be generated and set prior to adding to the Set
:
Example 143. Forcing the flush before adding to the Set
Book book1 = new Book();
book1.setTitle("High-Performance Java Persistence");
Book book2 = new Book();
book2.setTitle("Java Persistence with Hibernate");
Library library = doInJPA(this::entityManagerFactory, entityManager -> {
Library _library = entityManager.find(Library.class, 1L);
entityManager.persist(book1);
entityManager.persist(book2);
entityManager.flush();
_library.getBooks().add(book1);
_library.getBooks().add(book2);
return _library;
});
assertTrue(library.getBooks().contains(book1));
assertTrue(library.getBooks().contains(book2));
But this is often not feasible.
The final approach is to use a «better» equals/hashCode implementation, making use of a natural-id or business-key.
Example 144. Natural Id equals/hashCode
@Entity(name = "Library")
public static class Library {
@Id
private Long id;
private String name;
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "book_id")
private Set<Book> books = new HashSet<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
@NaturalId
private String isbn;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Book book = (Book) o;
return Objects.equals(isbn, book.isbn);
}
@Override
public int hashCode() {
return Objects.hash(isbn);
}
}
This time, when adding a Book
to the Library
Set
, you can retrieve the Book
even after it’s being persisted:
Example 145. Natural Id equals/hashCode persist example
Book book1 = new Book();
book1.setTitle("High-Performance Java Persistence");
book1.setIsbn("978-9730228236");
Library library = doInJPA(this::entityManagerFactory, entityManager -> {
Library _library = entityManager.find(Library.class, 1L);
_library.getBooks().add(book1);
return _library;
});
assertTrue(library.getBooks().contains(book1));
As you can see the question of equals/hashCode is not trivial, nor is there a one-size-fits-all solution.
Although using a natural-id is best for It’s possible to use the entity identifier for equality check, but it needs a workaround:
|
For details on mapping the identifier, see the Identifiers chapter.
2.4.8. Mapping the entity to a SQL query
You can map an entity to a SQL query using the @Subselect
annotation.
Example 146. @Subselect
entity mapping
@Entity(name = "Client")
@Table(name = "client")
public static class Client {
@Id
private Long id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
//Getters and setters omitted for brevity
}
@Entity(name = "Account")
@Table(name = "account")
public static class Account {
@Id
private Long id;
@ManyToOne
private Client client;
private String description;
//Getters and setters omitted for brevity
}
@Entity(name = "AccountTransaction")
@Table(name = "account_transaction")
public static class AccountTransaction {
@Id
@GeneratedValue
private Long id;
@ManyToOne
private Account account;
private Integer cents;
private String description;
//Getters and setters omitted for brevity
}
@Entity(name = "AccountSummary")
@Subselect(
"select " +
" a.id as id, " +
" concat(concat(c.first_name, ' '), c.last_name) as clientName, " +
" sum(atr.cents) as balance " +
"from account a " +
"join client c on c.id = a.client_id " +
"join account_transaction atr on a.id = atr.account_id " +
"group by a.id, concat(concat(c.first_name, ' '), c.last_name)"
)
@Synchronize({"client", "account", "account_transaction"})
public static class AccountSummary {
@Id
private Long id;
private String clientName;
private int balance;
//Getters and setters omitted for brevity
}
In the example above, the Account
entity does not retain any balance since every account operation is registered as an AccountTransaction
.
To find the Account
balance, we need to query the AccountSummary
which shares the same identifier with the Account
entity.
However, the AccountSummary
is not mapped to a physical table, but to an SQL query.
So, if we have the following AccountTransaction
record, the AccountSummary
balance will match the proper amount of money in this Account
.
Example 147. Finding a @Subselect
entity
scope.inTransaction(
(entityManager) -> {
Client client = new Client();
client.setId(1L);
client.setFirstName("John");
client.setLastName("Doe");
entityManager.persist(client);
Account account = new Account();
account.setId(1L);
account.setClient(client);
account.setDescription("Checking account");
entityManager.persist(account);
AccountTransaction transaction = new AccountTransaction();
transaction.setAccount(account);
transaction.setDescription("Salary");
transaction.setCents(100 * 7000);
entityManager.persist(transaction);
AccountSummary summary = entityManager.createQuery(
"select s " +
"from AccountSummary s " +
"where s.id = :id", AccountSummary.class)
.setParameter("id", account.getId())
.getSingleResult();
assertEquals("John Doe", summary.getClientName());
assertEquals(100 * 7000, summary.getBalance());
}
);
If we add a new AccountTransaction
entity and refresh the AccountSummary
entity, the balance is updated accordingly:
Example 148. Refreshing a @Subselect
entity
scope.inTransaction(
(entityManager) -> {
AccountSummary summary = entityManager.find(AccountSummary.class, 1L);
assertEquals("John Doe", summary.getClientName());
assertEquals(100 * 7000, summary.getBalance());
AccountTransaction transaction = new AccountTransaction();
transaction.setAccount(entityManager.getReference(Account.class, 1L));
transaction.setDescription("Shopping");
transaction.setCents(-100 * 2200);
entityManager.persist(transaction);
entityManager.flush();
entityManager.refresh(summary);
assertEquals(100 * 4800, summary.getBalance());
}
);
The goal of the With the |
2.4.9. Define a custom entity proxy
By default, when it needs to use a proxy instead of the actual POJO, Hibernate is going to use a Bytecode manipulation library like
Byte Buddy.
However, if the entity class is final, a proxy will not be created; you will get a POJO even when you only need a proxy reference.
In this case, you could proxy an interface that this particular entity implements, as illustrated by the following example.
Example 149. Final entity class implementing the Identifiable
interface
public interface Identifiable {
Long getId();
void setId(Long id);
}
@Entity(name = "Book")
@Proxy(proxyClass = Identifiable.class)
public static final class Book implements Identifiable {
@Id
private Long id;
private String title;
private String author;
@Override
public Long getId() {
return id;
}
@Override
public void setId(Long id) {
this.id = id;
}
//Other getters and setters omitted for brevity
}
The @Proxy
annotation is used to specify a custom proxy implementation for the current annotated entity.
When loading the Book
entity proxy, Hibernate is going to proxy the Identifiable
interface instead as illustrated by the following example:
Example 150. Proxying the final entity class implementing the Identifiable
interface
doInHibernate(this::sessionFactory, session -> {
Book book = new Book();
book.setId(1L);
book.setTitle("High-Performance Java Persistence");
book.setAuthor("Vlad Mihalcea");
session.persist(book);
});
doInHibernate(this::sessionFactory, session -> {
Identifiable book = session.getReference(Book.class, 1L);
assertTrue(
"Loaded entity is not an instance of the proxy interface",
book instanceof Identifiable
);
assertFalse(
"Proxy class was not created",
book instanceof Book
);
});
insert
into
Book
(author, title, id)
values
(?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [BIGINT] - [1]
As you can see in the associated SQL snippet, Hibernate issues no SQL SELECT query since the proxy can be
constructed without needing to fetch the actual entity POJO.
2.4.10. Define a custom entity persister
The @Persister
annotation is used to specify a custom entity or collection persister.
For entities, the custom persister must implement the EntityPersister
interface.
For collections, the custom persister must implement the CollectionPersister
interface.
Supplying a custom persister has been allowed historically, but has never been fully supported. Hibernate 6 provides better, alternative ways to accomplish the use cases for a custom persister. As of 6.2 @Persister has been formally deprecated.
|
Example 151. Entity persister mapping
@Entity
@Persister(impl = EntityPersister.class)
public class Author {
@Id
public Integer id;
@OneToMany(mappedBy = "author")
@Persister(impl = CollectionPersister.class)
public Set<Book> books = new HashSet<>();
//Getters and setters omitted for brevity
public void addBook(Book book) {
this.books.add(book);
book.setAuthor(this);
}
}
@Entity
@Persister(impl = EntityPersister.class)
public class Book {
@Id
public Integer id;
private String title;
@ManyToOne(fetch = FetchType.LAZY)
public Author author;
//Getters and setters omitted for brevity
}
By providing your own EntityPersister
and CollectionPersister
implementations,
you can control how entities and collections are persisted into the database.
2.5. Naming strategies
Part of the mapping of an object model to the relational database is
mapping names from the object model to the corresponding database names.
Hibernate looks at this as 2-stage process:
-
The first stage is determining a proper logical name from the domain model mapping. A
logical name can be either explicitly specified by the user (e.g., using@Column
or
@Table
) or it can be implicitly determined by Hibernate through an
ImplicitNamingStrategy contract. -
Second is the resolving of this logical name to a physical name which is defined
by the PhysicalNamingStrategy contract.
Historical NamingStrategy contract Historically Hibernate defined just a single Also, the NamingStrategy contract was often not flexible enough to properly apply a given naming Due to these limitations, |
At the core, the idea behind each naming strategy is to minimize the amount of
repetitive information a developer must provide for mapping a domain model.
Jakarta Persistence Compatibility Jakarta Persistence defines inherent rules about implicit logical name determination. If Jakarta Persistence provider Also, Jakarta Persistence defines no separation between logical and physical name. Following the Jakarta Persistence |
2.5.1. ImplicitNamingStrategy
When an entity does not explicitly name the database table that it maps to, we need
to implicitly determine that table name. Or when a particular attribute does not explicitly name
the database column that it maps to, we need to implicitly determine that column name. There are
examples of the role of the org.hibernate.boot.model.naming.ImplicitNamingStrategy
contract to
determine a logical name when the mapping did not provide an explicit name.
Hibernate defines multiple ImplicitNamingStrategy implementations out-of-the-box. Applications
are also free to plug in custom implementations.
There are multiple ways to specify the ImplicitNamingStrategy to use. First, applications can specify
the implementation using the hibernate.implicit_naming_strategy
configuration setting which accepts:
-
pre-defined «short names» for the out-of-the-box implementations
default
-
for
org.hibernate.boot.model.naming.ImplicitNamingStrategyJpaCompliantImpl
— an alias forjpa
jpa
-
for
org.hibernate.boot.model.naming.ImplicitNamingStrategyJpaCompliantImpl
— the Jakarta Persistence compliant naming strategy legacy-hbm
-
for
org.hibernate.boot.model.naming.ImplicitNamingStrategyLegacyHbmImpl
— compliant with the original Hibernate NamingStrategy legacy-jpa
-
for
org.hibernate.boot.model.naming.ImplicitNamingStrategyLegacyJpaImpl
— compliant with the legacy NamingStrategy developed for Java Persistence 1.0, which was unfortunately unclear in many respects regarding implicit naming rules component-path
-
for
org.hibernate.boot.model.naming.ImplicitNamingStrategyComponentPathImpl
— mostly followsImplicitNamingStrategyJpaCompliantImpl
rules, except that it uses the full composite paths, as opposed to just the ending property part
-
reference to a Class that implements the
org.hibernate.boot.model.naming.ImplicitNamingStrategy
contract -
FQN of a class that implements the
org.hibernate.boot.model.naming.ImplicitNamingStrategy
contract
Secondly, applications and integrations can leverage org.hibernate.boot.MetadataBuilder#applyImplicitNamingStrategy
to specify the ImplicitNamingStrategy to use. See
Bootstrap for additional details on bootstrapping.
2.5.2. PhysicalNamingStrategy
Many organizations define rules around the naming of database objects (tables, columns, foreign keys, etc).
The idea of a PhysicalNamingStrategy is to help implement such naming rules without having to hard-code them
into the mapping via explicit names.
While the purpose of an ImplicitNamingStrategy is to determine that an attribute named accountNumber
maps to
a logical column name of accountNumber
when not explicitly specified, the purpose of a PhysicalNamingStrategy
would be, for example, to say that the physical column name should instead be abbreviated to acct_num
.
It is true that the resolution to But the point here is the separation of concerns. The |
The default implementation is to simply use the logical name as the physical name. However
applications and integrations can define custom implementations of this PhysicalNamingStrategy
contract. Here is an example PhysicalNamingStrategy for a fictitious company named Acme Corp
whose naming standards are to:
-
prefer underscore-delimited words rather than camel casing
-
replace certain words with standard abbreviations
Example 152. Example PhysicalNamingStrategy implementation
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
* See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
*/
package org.hibernate.orm.test.naming;
import java.util.Arrays;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;
import org.hibernate.boot.model.naming.Identifier;
import org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl;
import org.hibernate.engine.jdbc.env.spi.JdbcEnvironment;
import org.junit.platform.commons.util.StringUtils;
/**
* An example PhysicalNamingStrategy that implements database object naming standards
* for our fictitious company Acme Corp.
* <p>
* In general Acme Corp prefers underscore-delimited words rather than camel casing.
* <p>
* Additionally standards call for the replacement of certain words with abbreviations.
*
* @author Steve Ebersole
* @author Nathan Xu
*/
public class AcmeCorpPhysicalNamingStrategy extends PhysicalNamingStrategyStandardImpl {
private static final Map<String, String> ABBREVIATIONS;
static {
ABBREVIATIONS = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
ABBREVIATIONS.put("account", "acct");
ABBREVIATIONS.put("number", "num");
}
@Override
public Identifier toPhysicalTableName(Identifier logicalName, JdbcEnvironment jdbcEnvironment) {
final List<String> parts = splitAndReplace( logicalName.getText());
return jdbcEnvironment.getIdentifierHelper().toIdentifier(
String.join("_", parts),
logicalName.isQuoted()
);
}
@Override
public Identifier toPhysicalSequenceName(Identifier logicalName, JdbcEnvironment jdbcEnvironment) {
final List<String> parts = splitAndReplace( logicalName.getText());
// Acme Corp says all sequences should end with _seq
if (!"seq".equals(parts.get(parts.size() - 1))) {
parts.add("seq");
}
return jdbcEnvironment.getIdentifierHelper().toIdentifier(
String.join("_", parts),
logicalName.isQuoted()
);
}
@Override
public Identifier toPhysicalColumnName(Identifier logicalName, JdbcEnvironment jdbcEnvironment) {
final List<String> parts = splitAndReplace( logicalName.getText());
return jdbcEnvironment.getIdentifierHelper().toIdentifier(
String.join("_", parts),
logicalName.isQuoted()
);
}
private List<String> splitAndReplace(String name) {
return Arrays.stream(splitByCharacterTypeCamelCase(name))
.filter(StringUtils::isNotBlank)
.map(p -> ABBREVIATIONS.getOrDefault(p, p).toLowerCase(Locale.ROOT))
.collect(Collectors.toList());
}
private String[] splitByCharacterTypeCamelCase(String s) {
return s.split( "(?<!(^|[A-Z]))(?=[A-Z])|(?<!^)(?=[A-Z][a-z])" );
}
}
There are multiple ways to specify the PhysicalNamingStrategy to use. First, applications can specify
the implementation using the hibernate.physical_naming_strategy
configuration setting which accepts:
-
reference to a Class that implements the
org.hibernate.boot.model.naming.PhysicalNamingStrategy
contract -
FQN of a class that implements the
org.hibernate.boot.model.naming.PhysicalNamingStrategy
contract
Secondly, applications and integrations can leverage org.hibernate.boot.MetadataBuilder#applyPhysicalNamingStrategy
.
See Bootstrap for additional details on bootstrapping.
2.6. Access strategies
As a Jakarta Persistence provider, Hibernate can introspect both the entity attributes (instance fields) or the accessors (instance properties).
By default, the placement of the @Id
annotation gives the default access strategy.
When placed on a field, Hibernate will assume field-based access.
When placed on the identifier getter, Hibernate will use property-based access.
Embeddable types inherit the access strategy from their parent entities.
2.6.1. Field-based access
Example 153. Field-based access
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
When using field-based access, adding other entity-level methods is much more flexible because Hibernate won’t consider those part of the persistence state.
To exclude a field from being part of the entity persistent state, the field must be marked with the @Transient
annotation.
Another advantage of using field-based access is that some entity attributes can be hidden from outside the entity. An example of such attribute is the entity With field-based access, we can simply omit the getter and the setter for this version field, and Hibernate can still leverage the optimistic concurrency control mechanism. |
2.6.2. Property-based access
Example 154. Property-based access
@Entity(name = "Book")
public static class Book {
private Long id;
private String title;
private String author;
@Id
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
}
When using property-based access, Hibernate uses the accessors for both reading and writing the entity state.
Every other method that will be added to the entity (e.g. helper methods for synchronizing both ends of a bidirectional one-to-many association) will have to be marked with the @Transient
annotation.
2.6.3. Overriding the default access strategy
The default access strategy mechanism can be overridden with the Jakarta Persistence @Access
annotation.
In the following example, the @Version
attribute is accessed by its field and not by its getter, like the rest of entity attributes.
Example 155. Overriding access strategy
@Entity(name = "Book")
public static class Book {
private Long id;
private String title;
private String author;
@Access(AccessType.FIELD)
@Version
private int version;
@Id
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
}
2.6.4. Embeddable types and access strategy
Because embeddables are managed by their owning entities, the access strategy is therefore inherited from the entity too.
This applies to both simple embeddable types as well as for collection of embeddables.
The embeddable types can overrule the default implicit access strategy (inherited from the owning entity).
In the following example, the embeddable uses property-based access, no matter what access strategy the owning entity is choosing:
Example 156. Embeddable with exclusive access strategy
@Embeddable
@Access(AccessType.PROPERTY)
public static class Author {
private String firstName;
private String lastName;
public Author() {
}
public Author(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
The owning entity can use field-based access while the embeddable uses property-based access as it has chosen explicitly:
Example 157. Entity including a single embeddable type
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
@Embedded
private Author author;
//Getters and setters are omitted for brevity
}
This works also for collection of embeddable types:
Example 158. Entity including a collection of embeddable types
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
@ElementCollection
@CollectionTable(
name = "book_author",
joinColumns = @JoinColumn(name = "book_id")
)
private List<Author> authors = new ArrayList<>();
//Getters and setters are omitted for brevity
}
2.7. Identifiers
Identifiers model the primary key of an entity. They are used to uniquely identify each specific entity.
Hibernate and Jakarta Persistence both make the following assumptions about the corresponding database column(s):
UNIQUE
-
The values must uniquely identify each row.
NOT NULL
-
The values cannot be null. For composite ids, no part can
be null. IMMUTABLE
-
The values, once inserted, can never be changed. In cases where the values for the PK you have
chosen will be updated, Hibernate recommends mapping the mutable value as a natural id, and use a surrogate id
for the PK. See Natural Ids.
Technically the identifier does not have to map to the column(s) physically defined as the table primary key. |
Every entity must define an identifier. For entity inheritance hierarchies, the identifier must be defined just on the entity that is the root of the hierarchy.
An identifier may be simple or composite.
2.7.1. Simple identifiers
Simple identifiers map to a single basic attribute, and are denoted using the jakarta.persistence.Id
annotation.
According to Jakarta Persistence, only the following types are portably supported for use as identifier attribute types:
-
any Java primitive type
-
any primitive wrapper type
-
java.lang.String
-
java.util.Date
(TemporalType#DATE
) -
java.sql.Date
-
java.math.BigDecimal
-
java.math.BigInteger
Hibernate, however, supports a more broad set of types to be used for identifiers (UUID
, e.g.).
Assigned identifiers
Values for simple identifiers can be assigned, which simply means that the application itself will
assign the value to the identifier attribute prior to persisting the entity.
Example 159. Simple assigned entity identifier
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
Generated identifiers
Values for simple identifiers can be generated. To denote that an identifier attribute is generated, it is
annotated with jakarta.persistence.GeneratedValue
Example 160. Simple generated identifier
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
When an entity with an identifier defined as generated is persisted, Hibernate will generate the value based on
an associated generation strategy. Identifier value generations strategies are discussed in detail in the
Generated identifier values section.
While Hibernate supports almost any valid basic type be used for generated identifier values, |
2.7.2. Composite identifiers
Composite identifiers correspond to one or more persistent attributes.
Here are the rules governing composite identifiers, as defined by the Jakarta Persistence specification:
-
The composite identifier must be represented by a «primary key class».
The primary key class may be defined using thejakarta.persistence.EmbeddedId
annotation (see Composite identifiers with@EmbeddedId
),
or defined using thejakarta.persistence.IdClass
annotation (see Composite identifiers with@IdClass
). -
The primary key class must be public and must have a public no-arg constructor.
-
The primary key class must be serializable.
-
The primary key class must define equals and hashCode methods, consistent with equality for the underlying database types to which the primary key is mapped.
The restriction that a composite identifier has to be represented by a «primary key class» (e.g. Hibernate does allow composite identifiers to be defined without a «primary key class» via multiple |
The attributes making up the composition can be either basic, composite or @ManyToOne
. Note especially that collection and one-to-one
are never appropriate.
2.7.3. Composite identifiers with @EmbeddedId
Modeling a composite identifier using an EmbeddedId simply means defining an embeddable to be a composition for the attributes making up
the identifier, and then exposing an attribute of that embeddable type on the entity.
Example 161. Basic @EmbeddedId
@Entity(name = "SystemUser")
public static class SystemUser {
@EmbeddedId
private PK pk;
private String name;
//Getters and setters are omitted for brevity
}
@Embeddable
public static class PK implements Serializable {
private String subsystem;
private String username;
public PK(String subsystem, String username) {
this.subsystem = subsystem;
this.username = username;
}
private PK() {
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
PK pk = (PK) o;
return Objects.equals(subsystem, pk.subsystem) &&
Objects.equals(username, pk.username);
}
@Override
public int hashCode() {
return Objects.hash(subsystem, username);
}
}
As mentioned before, EmbeddedIds can even contain @ManyToOne
attributes:
Example 162. @EmbeddedId
with @ManyToOne
@Entity(name = "SystemUser")
public static class SystemUser {
@EmbeddedId
private PK pk;
private String name;
//Getters and setters are omitted for brevity
}
@Entity(name = "Subsystem")
public static class Subsystem {
@Id
private String id;
private String description;
//Getters and setters are omitted for brevity
}
@Embeddable
public static class PK implements Serializable {
@ManyToOne(fetch = FetchType.LAZY)
private Subsystem subsystem;
private String username;
public PK(Subsystem subsystem, String username) {
this.subsystem = subsystem;
this.username = username;
}
private PK() {
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
PK pk = (PK) o;
return Objects.equals(subsystem, pk.subsystem) &&
Objects.equals(username, pk.username);
}
@Override
public int hashCode() {
return Objects.hash(subsystem, username);
}
}
Hibernate supports directly modeling However, that is not portably supported by the Jakarta Persistence specification. |
2.7.4. Composite identifiers with @IdClass
Modeling a composite identifier using an IdClass differs from using an EmbeddedId in that the entity defines each individual
attribute making up the composition. The IdClass is used as the representation of the identifier for load-by-id operations.
Example 163. Basic @IdClass
@Entity(name = "SystemUser")
@IdClass(PK.class)
public static class SystemUser {
@Id
private String subsystem;
@Id
private String username;
private String name;
public PK getId() {
return new PK(
subsystem,
username
);
}
public void setId(PK id) {
this.subsystem = id.getSubsystem();
this.username = id.getUsername();
}
//Getters and setters are omitted for brevity
}
public static class PK implements Serializable {
private String subsystem;
private String username;
public PK(String subsystem, String username) {
this.subsystem = subsystem;
this.username = username;
}
private PK() {
}
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
PK pk = (PK) o;
return Objects.equals(subsystem, pk.subsystem) &&
Objects.equals(username, pk.username);
}
@Override
public int hashCode() {
return Objects.hash(subsystem, username);
}
}
Non-aggregated composite identifiers can also contain ManyToOne attributes as we saw with aggregated mappings, though still non-portably.
Example 164. IdClass with @ManyToOne
@Entity(name = "SystemUser")
@IdClass(PK.class)
public static class SystemUser {
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Subsystem subsystem;
@Id
private String username;
private String name;
//Getters and setters are omitted for brevity
}
@Entity(name = "Subsystem")
public static class Subsystem {
@Id
private String id;
private String description;
//Getters and setters are omitted for brevity
}
public static class PK implements Serializable {
private Subsystem subsystem;
private String username;
public PK(Subsystem subsystem, String username) {
this.subsystem = subsystem;
this.username = username;
}
private PK() {
}
//Getters and setters are omitted for brevity
}
With non-aggregated composite identifiers, Hibernate also supports «partial» generation of the composite values.
Example 165. @IdClass
with partial identifier generation using @GeneratedValue
@Entity(name = "SystemUser")
@IdClass(PK.class)
public static class SystemUser {
@Id
private String subsystem;
@Id
private String username;
@Id
@GeneratedValue
private Integer registrationId;
private String name;
public PK getId() {
return new PK(
subsystem,
username,
registrationId
);
}
public void setId(PK id) {
this.subsystem = id.getSubsystem();
this.username = id.getUsername();
this.registrationId = id.getRegistrationId();
}
//Getters and setters are omitted for brevity
}
public static class PK implements Serializable {
private String subsystem;
private String username;
private Integer registrationId;
public PK(String subsystem, String username) {
this.subsystem = subsystem;
this.username = username;
}
public PK(String subsystem, String username, Integer registrationId) {
this.subsystem = subsystem;
this.username = username;
this.registrationId = registrationId;
}
private PK() {
}
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
PK pk = (PK) o;
return Objects.equals(subsystem, pk.subsystem) &&
Objects.equals(username, pk.username) &&
Objects.equals(registrationId, pk.registrationId);
}
@Override
public int hashCode() {
return Objects.hash(subsystem, username, registrationId);
}
}
This feature which allows auto-generated values in composite identifiers exists because of a highly questionable interpretation Hibernate does not feel that Jakarta Persistence defines support for this, but added the feature simply to be usable in SpecJ |
2.7.5. Composite identifiers with associations
Hibernate allows defining a composite identifier out of entity associations.
In the following example, the Book
entity identifier is formed of two @ManyToOne
associations.
Example 166. Composite identifiers with associations
@Entity(name = "Book")
public static class Book implements Serializable {
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Author author;
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Publisher publisher;
@Id
private String title;
public Book(Author author, Publisher publisher, String title) {
this.author = author;
this.publisher = publisher;
this.title = title;
}
private Book() {
}
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Book book = (Book) o;
return Objects.equals(author, book.author) &&
Objects.equals(publisher, book.publisher) &&
Objects.equals(title, book.title);
}
@Override
public int hashCode() {
return Objects.hash(author, publisher, title);
}
}
@Entity(name = "Author")
public static class Author implements Serializable {
@Id
private String name;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Author author = (Author) o;
return Objects.equals(name, author.name);
}
@Override
public int hashCode() {
return Objects.hash(name);
}
}
@Entity(name = "Publisher")
public static class Publisher implements Serializable {
@Id
private String name;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Publisher publisher = (Publisher) o;
return Objects.equals(name, publisher.name);
}
@Override
public int hashCode() {
return Objects.hash(name);
}
}
Although the mapping is much simpler than using an @EmbeddedId
or an @IdClass
, there’s no separation between the entity instance and the actual identifier.
To query this entity, an instance of the entity itself must be supplied to the persistence context.
Example 167. Fetching with composite identifiers
Book book = entityManager.find(Book.class, new Book(
author,
publisher,
"High-Performance Java Persistence"
));
assertEquals("Vlad Mihalcea", book.getAuthor().getName());
2.7.6. Composite identifiers with generated properties
When using composite identifiers, the underlying identifier properties must be manually assigned by the user.
Automatically generated properties are not supported to be used to generate the value of an underlying property that makes the composite identifier.
Therefore, you cannot use any of the automatic property generator described by the generated properties section like @Generated
, @CreationTimestamp
or @ValueGenerationType
or database-generated values.
Nevertheless, you can still generate the identifier properties prior to constructing the composite identifier, as illustrated by the following examples.
Assuming we have the following EventId
composite identifier and an Event
entity which uses the aforementioned composite identifier.
Example 168. The Event entity and EventId composite identifier
@Entity
class Event {
@Id
private EventId id;
@Column(name = "event_key")
private String key;
@Column(name = "event_value")
private String value;
//Getters and setters are omitted for brevity
}
@Embeddable
class EventId implements Serializable {
private Integer category;
private Timestamp createdOn;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
EventId that = (EventId) o;
return Objects.equals(category, that.category) &&
Objects.equals(createdOn, that.createdOn);
}
@Override
public int hashCode() {
return Objects.hash(category, createdOn);
}
}
In-memory generated composite identifier properties
If you want to generate the composite identifier properties in-memory,
you need to do that as follows:
Example 169. In-memory generated composite identifier properties example
EventId id = new EventId();
id.setCategory(1);
id.setCreatedOn(new Timestamp(System.currentTimeMillis()));
Event event = new Event();
event.setId(id);
event.setKey("Temperature");
event.setValue("9");
entityManager.persist(event);
Notice that the createdOn
property of the EventId
composite identifier was generated by the data access code and assigned to the
identifier prior to persisting the Event
entity.
Database generated composite identifier properties
If you want to generate the composite identifier properties using a database function or stored procedure,
you could to do it as illustrated by the following example.
Example 170. Database generated composite identifier properties example
OffsetDateTime currentTimestamp = (OffsetDateTime) entityManager
.createNativeQuery(
"SELECT CURRENT_TIMESTAMP", OffsetDateTime.class)
.getSingleResult();
EventId id = new EventId();
id.setCategory(1);
id.setCreatedOn(Timestamp.from(currentTimestamp.toInstant()));
Event event = new Event();
event.setId(id);
event.setKey("Temperature");
event.setValue("9");
entityManager.persist(event);
Notice that the createdOn
property of the EventId
composite identifier was generated by calling the CURRENT_TIMESTAMP
database function,
and we assigned it to the composite identifier prior to persisting the Event
entity.
2.7.7. Generated identifier values
Hibernate supports identifier value generation across a number of different types.
Remember that Jakarta Persistence portably defines identifier value generation just for integer types.
You can also auto-generate values for non-identifier attributes. For more details, see the Generated properties section. |
Identifier value generation is indicated using the jakarta.persistence.GeneratedValue
annotation.
The most important piece of information here is the specified jakarta.persistence.GenerationType
which indicates how values will be generated.
AUTO
(the default)-
Indicates that the persistence provider (Hibernate) should choose an appropriate generation strategy. See Interpreting AUTO.
IDENTITY
-
Indicates that database IDENTITY columns will be used for primary key value generation. See Using IDENTITY columns.
SEQUENCE
-
Indicates that database sequence should be used for obtaining primary key values. See Using sequences.
TABLE
-
Indicates that a database table should be used for obtaining primary key values. See Using the table identifier generator.
2.7.8. Interpreting AUTO
How a persistence provider interprets the AUTO generation type is left up to the provider.
The default behavior is to look at the Java type of the identifier attribute, plus what the underlying database supports.
If the identifier type is UUID, Hibernate is going to use a UUID identifier.
If the identifier type is numeric (e.g. Long
, Integer
), then Hibernate will use its SequenceStyleGenerator
which
resolves to a SEQUENCE generation if the underlying database supports sequences and a table-based generation otherwise.
2.7.9. Using sequences
For implementing database sequence-based identifier value generation Hibernate makes use of its
org.hibernate.id.enhanced.SequenceStyleGenerator
id generator. It is important to note that SequenceStyleGenerator
is capable of working against databases that do not support sequences by transparently switching to a table as the
underlying backing, which gives Hibernate a huge degree of portability across databases while still maintaining consistent
id generation behavior (versus say choosing between SEQUENCE and IDENTITY).
Example 171. Implicit sequence
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue( strategy = SEQUENCE )
private Long id;
@Column(name = "product_name")
private String name;
//Getters and setters are omitted for brevity
}
Notice that the mapping does not specify the name of the sequence to use. In such cases, Hibernate will assume a
sequence name based on the name of the table to which the entity is mapped. Here, since the entity is mapped to
a table named product
, Hibernate will use a sequence named product_seq
.
When using |
To specify the sequence name explicitly, the simplest form is to specify @GeneratedValue#generator
.
Example 172. Named sequence
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue(
strategy = SEQUENCE,
generator = "explicit_product_sequence"
)
private Long id;
@Column(name = "product_name")
private String name;
//Getters and setters are omitted for brevity
}
For this mapping, Hibernate will use explicit_product_sequence
as the name of the sequence.
For more advanced configuration, Jakarta Persistence defines the @SequenceGenerator
annotation.
Example 173. Simple @SequenceGenerator
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue(
strategy = SEQUENCE,
generator = "sequence-generator"
)
@SequenceGenerator(
name = "sequence-generator",
sequenceName = "explicit_product_sequence"
)
private Long id;
@Column(name = "product_name")
private String name;
//Getters and setters are omitted for brevity
}
This is simply a more verbose form of the mapping in Named sequence.
However, the jakarta.persistence.SequenceGenerator
annotation allows you to specify additional
configurations as well.
Example 174. Sequence configuration
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue(
strategy = GenerationType.SEQUENCE,
generator = "sequence-generator"
)
@SequenceGenerator(
name = "sequence-generator",
sequenceName = "explicit_product_sequence",
allocationSize = 5
)
private Long id;
@Column(name = "product_name")
private String name;
//Getters and setters are omitted for brevity
}
Again the mapping specifies explicit_product_sequence
as the physical sequence name, but it also specifies an
explicit allocation-size («increment by»).
2.7.10. Using IDENTITY columns
For implementing identifier value generation based on IDENTITY columns,
Hibernate makes use of its org.hibernate.id.IdentityGenerator
id generator which expects the identifier to be generated by INSERT into the table.
IdentityGenerator understands 3 different ways that the INSERT-generated value might be retrieved:
-
If Hibernate believes the JDBC environment supports
java.sql.Statement#getGeneratedKeys
, then that approach will be used for extracting the IDENTITY generated keys. -
Otherwise, if
Dialect#supportsInsertSelectIdentity
reports true, Hibernate will use the Dialect specific INSERT+SELECT statement syntax. -
Otherwise, Hibernate will expect that the database supports some form of asking for the most recently inserted IDENTITY value via a separate SQL command as indicated by
Dialect#getIdentitySelectString
.
It is important to realize that using IDENTITY columns imposes a runtime behavior where the entity This can mess up extended persistence contexts (long conversations). In Hibernate 5.3, Hibernate attempts to delay the insert of entities if the flush-mode does not equal In Hibernate 5.4, Hibernate attempts to remedy the problem using an algorithm to decide if the insert should Entity mappings can sometimes be complex and it is possible a corner case was overlooked. Hibernate offers a This configuration option is meant to act as a temporary fix and bridge the gap between the changes in this |
There is yet another important runtime impact of choosing IDENTITY generation: Hibernate will not be able to batch INSERT statements for the entities using the IDENTITY generation. The importance of this depends on the application-specific use cases. |
2.7.11. Using the table identifier generator
Hibernate achieves table-based identifier generation based on its org.hibernate.id.enhanced.TableGenerator
which defines a table capable of holding multiple named value segments for any number of entities.
The basic idea is that a given table-generator table (hibernate_sequences
for example) can hold multiple segments of identifier generation values.
Example 175. Unnamed table generator
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue(
strategy = GenerationType.TABLE
)
private Long id;
@Column(name = "product_name")
private String name;
//Getters and setters are omitted for brevity
}
create table hibernate_sequences (
sequence_name varchar2(255 char) not null,
next_val number(19,0),
primary key (sequence_name)
)
If no table name is given Hibernate assumes an implicit name of hibernate_sequences
.
Additionally, because no jakarta.persistence.TableGenerator#pkColumnValue
is specified,
Hibernate will use the default segment (sequence_name='default'
) from the hibernate_sequences table.
However, you can configure the table identifier generator using the @TableGenerator
annotation.
Example 176. Configured table generator
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue(
strategy = GenerationType.TABLE,
generator = "table-generator"
)
@TableGenerator(
name = "table-generator",
table = "table_identifier",
pkColumnName = "table_name",
valueColumnName = "product_id",
allocationSize = 5
)
private Long id;
@Column(name = "product_name")
private String name;
//Getters and setters are omitted for brevity
}
create table table_identifier (
table_name varchar2(255 char) not null,
product_id number(19,0),
primary key (table_name)
)
Now, when inserting 3 Product
entities, Hibernate generates the following statements:
Example 177. Configured table generator persist example
for (long i = 1; i <= 3; i++) {
Product product = new Product();
product.setName(String.format("Product %d", i));
entityManager.persist(product);
}
select
tbl.product_id
from
table_identifier tbl
where
tbl.table_name = ?
for update
-- binding parameter [1] - [Product]
insert
into
table_identifier
(table_name, product_id)
values
(?, ?)
-- binding parameter [1] - [Product]
-- binding parameter [2] - [1]
update
table_identifier
set
product_id= ?
where
product_id= ?
and table_name= ?
-- binding parameter [1] - [6]
-- binding parameter [2] - [1]
select
tbl.product_id
from
table_identifier tbl
where
tbl.table_name= ? for update
update
table_identifier
set
product_id= ?
where
product_id= ?
and table_name= ?
-- binding parameter [1] - [11]
-- binding parameter [2] - [6]
insert
into
Product
(product_name, id)
values
(?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 1]
-- binding parameter [2] as [BIGINT] - [1]
insert
into
Product
(product_name, id)
values
(?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 2]
-- binding parameter [2] as [BIGINT] - [2]
insert
into
Product
(product_name, id)
values
(?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 3]
-- binding parameter [2] as [BIGINT] - [3]
2.7.12. Using UUID generation
As mentioned above, Hibernate supports UUID identifier value generation.
This is supported through its org.hibernate.id.UUIDGenerator
id generator.
- NOTE
-
org.hibernate.id.UUIDGenerator
is an example of@IdGeneratorType
discussed in Using@IdGeneratorType
UUIDGenerator
supports pluggable strategies for exactly how the UUID is generated.
These strategies are defined by the org.hibernate.id.UUIDGenerationStrategy
contract.
The default strategy is a version 4 (random) strategy according to IETF RFC 4122.
Hibernate does ship with an alternative strategy which is a RFC 4122 version 1 (time-based) strategy (using IP address rather than mac address).
Example 178. Implicitly using the random UUID strategy
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue
private UUID id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
To specify an alternative generation strategy, we’d have to define some configuration via @GenericGenerator
.
Here we choose the RFC 4122 version 1 compliant strategy named org.hibernate.id.uuid.CustomVersionOneStrategy
.
Example 179. Implicitly using the random UUID strategy
@Entity(name = "Book")
public static class Book {
@Id
@GeneratedValue(generator = "custom-uuid")
@GenericGenerator(
name = "custom-uuid",
strategy = "org.hibernate.id.UUIDGenerator",
parameters = {
@Parameter(
name = "uuid_gen_strategy_class",
value = "org.hibernate.id.uuid.CustomVersionOneStrategy"
)
}
)
private UUID id;
private String title;
private String author;
//Getters and setters are omitted for brevity
}
2.7.13. Optimizers
Most of the Hibernate generators that separately obtain identifier values from database structures support the use of pluggable optimizers.
Optimizers help manage the number of times Hibernate has to talk to the database in order to generate identifier values.
For example, with no optimizer applied to a sequence-generator, every time the application asked Hibernate to generate an identifier it would need to grab the next sequence value from the database.
But if we can minimize the number of times we need to communicate with the database here, the application will be able to perform better,
which is, in fact, the role of these optimizers.
- none
-
No optimization is performed. We communicate with the database each and every time an identifier value is needed from the generator.
- pooled-lo
-
The pooled-lo optimizer works on the principle that the increment-value is encoded into the database table/sequence structure.
In sequence-terms, this means that the sequence is defined with a greater-than-1 increment size.For example, consider a brand new sequence defined as
create sequence m_sequence start with 1 increment by 20
.
This sequence essentially defines a «pool» of 20 usable id values each and every time we ask it for its next-value.
The pooled-lo optimizer interprets the next-value as the low end of that pool.So when we first ask it for next-value, we’d get 1.
We then assume that the valid pool would be the values from 1-20 inclusive.The next call to the sequence would result in 21, which would define 21-40 as the valid range. And so on.
The «lo» part of the name indicates that the value from the database table/sequence is interpreted as the pool lo(w) end. - pooled
-
Just like pooled-lo, except that here the value from the table/sequence is interpreted as the high end of the value pool.
- hilo; legacy-hilo
-
Define a custom algorithm for generating pools of values based on a single value from a table or sequence.
These optimizers are not recommended for use. They are maintained (and mentioned) here simply for use by legacy applications that used these strategies previously.
Applications can also implement and use their own optimizer strategies, as defined by the |
2.7.14. Using @IdGeneratorType
@IdGeneratorType
is a meta-annotation that allows the creation of custom annotations that support simple, concise
and type-safe definition and configuration of custom org.hibernate.id.IdentifierGenerator
implementations.
Example 180. @IdGeneratorType
public class CustomSequenceGenerator implements IdentifierGenerator {
public CustomSequenceGenerator(
Sequence config,
Member annotatedMember,
CustomIdGeneratorCreationContext context) {
//...
}
@Override
public Object generate(
SharedSessionContractImplementor session,
Object object) {
//...
}
@IdGeneratorType( CustomSequenceGenerator.class )
@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface Sequence {
String name();
int startWith() default 1;
int incrementBy() default 50;
Class<? extends Optimizer> optimizer() default Optimizer.class;
}
The example illustrates using @IdGeneratorType
to define a custom sequence-based annotation @Sequence
to apply and configure a custom IdentifierGenerator
implementation CustomSequenceGenerator
.
Notice the CustomSequenceGenerator
constructor. Custom generator defined through @IdGeneratorType
receive the following arguments:
-
The configuration annotation — here,
@Sequence
. This is the type-safety aspect, rather than
relying on untyped configuration properties in a Map, etc. -
The
Member
to which annotation was applied. This allows access to the Java type of the identifier
attribute, etc. -
CustomIdGeneratorCreationContext
is a «parameter object» providing access to things often useful
for identifier generators.
2.7.15. Using @GenericGenerator
|
@GenericGenerator
allows integration of any Hibernate org.hibernate.id.IdentifierGenerator
implementation, including any of the specific ones discussed here and any custom ones.
Example 181. Pooled-lo optimizer mapping using @GenericGenerator
mapping
@Entity(name = "Product")
public static class Product {
@Id
@GeneratedValue(
strategy = GenerationType.SEQUENCE,
generator = "product_generator"
)
@GenericGenerator(
name = "product_generator",
type = org.hibernate.id.enhanced.SequenceStyleGenerator.class,
parameters = {
@Parameter(name = "sequence_name", value = "product_sequence"),
@Parameter(name = "initial_value", value = "1"),
@Parameter(name = "increment_size", value = "3"),
@Parameter(name = "optimizer", value = "pooled-lo")
}
)
private Long id;
@Column(name = "p_name")
private String name;
@Column(name = "p_number")
private String number;
//Getters and setters are omitted for brevity
}
Now, when saving 5 Person
entities and flushing the Persistence Context after every 3 entities:
Example 182. Pooled-lo optimizer mapping using @GenericGenerator
mapping
for (long i = 1; i <= 5; i++) {
if(i % 3 == 0) {
entityManager.flush();
}
Product product = new Product();
product.setName(String.format("Product %d", i));
product.setNumber(String.format("P_100_%d", i));
entityManager.persist(product);
}
CALL NEXT VALUE FOR product_sequence
INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 1]
-- binding parameter [2] as [VARCHAR] - [P_100_1]
-- binding parameter [3] as [BIGINT] - [1]
INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 2]
-- binding parameter [2] as [VARCHAR] - [P_100_2]
-- binding parameter [3] as [BIGINT] - [2]
CALL NEXT VALUE FOR product_sequence
INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 3]
-- binding parameter [2] as [VARCHAR] - [P_100_3]
-- binding parameter [3] as [BIGINT] - [3]
INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 4]
-- binding parameter [2] as [VARCHAR] - [P_100_4]
-- binding parameter [3] as [BIGINT] - [4]
INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Product 5]
-- binding parameter [2] as [VARCHAR] - [P_100_5]
-- binding parameter [3] as [BIGINT] - [5]
As you can see from the list of generated SQL statements, you can insert 3 entities with just one database sequence call.
This way, the pooled and the pooled-lo optimizers allow you to reduce the number of database roundtrips, therefore reducing the overall transaction response time.
2.7.16. Derived Identifiers
Java Persistence 2.0 added support for derived identifiers which allow an entity to borrow the identifier from a many-to-one or one-to-one association.
Example 183. Derived identifier with @MapsId
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@NaturalId
private String registrationNumber;
public Person() {}
public Person(String registrationNumber) {
this.registrationNumber = registrationNumber;
}
//Getters and setters are omitted for brevity
}
@Entity(name = "PersonDetails")
public static class PersonDetails {
@Id
private Long id;
private String nickName;
@OneToOne
@MapsId
private Person person;
//Getters and setters are omitted for brevity
}
In the example above, the PersonDetails
entity uses the id
column for both the entity identifier and for the one-to-one association to the Person
entity.
The value of the PersonDetails
entity identifier is «derived» from the identifier of its parent Person
entity.
Example 184. Derived identifier with @MapsId
persist example
doInJPA(this::entityManagerFactory, entityManager -> {
Person person = new Person("ABC-123");
person.setId(1L);
entityManager.persist(person);
PersonDetails personDetails = new PersonDetails();
personDetails.setNickName("John Doe");
personDetails.setPerson(person);
entityManager.persist(personDetails);
});
doInJPA(this::entityManagerFactory, entityManager -> {
PersonDetails personDetails = entityManager.find(PersonDetails.class, 1L);
assertEquals("John Doe", personDetails.getNickName());
});
The @MapsId
annotation can also reference columns from an @EmbeddedId
identifier as well.
The previous example can also be mapped using @PrimaryKeyJoinColumn
.
Example 185. Derived identifier @PrimaryKeyJoinColumn
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@NaturalId
private String registrationNumber;
public Person() {}
public Person(String registrationNumber) {
this.registrationNumber = registrationNumber;
}
//Getters and setters are omitted for brevity
}
@Entity(name = "PersonDetails")
public static class PersonDetails {
@Id
private Long id;
private String nickName;
@OneToOne
@PrimaryKeyJoinColumn
private Person person;
public void setPerson(Person person) {
this.person = person;
this.id = person.getId();
}
//Other getters and setters are omitted for brevity
}
Unlike |
2.7.17. @RowId
If you annotate a given entity with the @RowId
annotation and the underlying database supports fetching a record by ROWID (e.g. Oracle),
then Hibernate can use the ROWID
pseudo-column for CRUD operations.
Example 186. @RowId
entity mapping
@Entity(name = "Product")
@RowId("ROWID")
public static class Product {
@Id
private Long id;
@Column(name = "`name`")
private String name;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
Now, when fetching an entity and modifying it, Hibernate uses the ROWID
pseudo-column for the UPDATE SQL statement.
Example 187. @RowId
example
Product product = entityManager.find(Product.class, 1L);
product.setName("Smart phone");
SELECT
p.id as id1_0_0_,
p."name" as name2_0_0_,
p."number" as number3_0_0_,
p.ROWID as rowid_0_
FROM
Product p
WHERE
p.id = ?
-- binding parameter [1] as [BIGINT] - [1]
-- extracted value ([name2_0_0_] : [VARCHAR]) - [Mobile phone]
-- extracted value ([number3_0_0_] : [VARCHAR]) - [123-456-7890]
-- extracted ROWID value: AAAwkBAAEAAACP3AAA
UPDATE
Product
SET
"name" = ?,
"number" = ?
WHERE
ROWID = ?
-- binding parameter [1] as [VARCHAR] - [Smart phone]
-- binding parameter [2] as [VARCHAR] - [123-456-7890]
-- binding parameter [3] as ROWID - [AAAwkBAAEAAACP3AAA]
2.8. Associations
Associations describe how two or more entities form a relationship based on a database joining semantics.
2.8.1. @ManyToOne
@ManyToOne
is the most common association, having a direct equivalent in the relational database as well (e.g. foreign key),
and so it establishes a relationship between a child entity and a parent.
Example 188. @ManyToOne
association
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
@Column(name = "`number`")
private String number;
@ManyToOne
@JoinColumn(name = "person_id",
foreignKey = @ForeignKey(name = "PERSON_ID_FK")
)
private Person person;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
person_id BIGINT ,
PRIMARY KEY ( id )
)
ALTER TABLE Phone
ADD CONSTRAINT PERSON_ID_FK
FOREIGN KEY (person_id) REFERENCES Person
Each entity has a lifecycle of its own. Once the @ManyToOne
association is set, Hibernate will set the associated database foreign key column.
Example 189. @ManyToOne
association lifecycle
Person person = new Person();
entityManager.persist(person);
Phone phone = new Phone("123-456-7890");
phone.setPerson(person);
entityManager.persist(phone);
entityManager.flush();
phone.setPerson(null);
INSERT INTO Person ( id )
VALUES ( 1 )
INSERT INTO Phone ( number, person_id, id )
VALUES ( '123-456-7890', 1, 2 )
UPDATE Phone
SET number = '123-456-7890',
person_id = NULL
WHERE id = 2
2.8.2. @OneToMany
The @OneToMany
association links a parent entity with one or more child entities.
If the @OneToMany
doesn’t have a mirroring @ManyToOne
association on the child side, the @OneToMany
association is unidirectional.
If there is a @ManyToOne
association on the child side, the @OneToMany
association is bidirectional and the application developer can navigate this relationship from both ends.
Unidirectional @OneToMany
When using a unidirectional @OneToMany
association, Hibernate resorts to using a link table between the two joining entities.
Example 190. Unidirectional @OneToMany
association
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Person_Phone (
Person_id BIGINT NOT NULL ,
phones_id BIGINT NOT NULL
)
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
PRIMARY KEY ( id )
)
ALTER TABLE Person_Phone
ADD CONSTRAINT UK_9uhc5itwc9h5gcng944pcaslf
UNIQUE (phones_id)
ALTER TABLE Person_Phone
ADD CONSTRAINT FKr38us2n8g5p9rj0b494sd3391
FOREIGN KEY (phones_id) REFERENCES Phone
ALTER TABLE Person_Phone
ADD CONSTRAINT FK2ex4e4p7w1cj310kg2woisjl2
FOREIGN KEY (Person_id) REFERENCES Person
The |
Example 191. Cascading @OneToMany
association
Person person = new Person();
Phone phone1 = new Phone("123-456-7890");
Phone phone2 = new Phone("321-654-0987");
person.getPhones().add(phone1);
person.getPhones().add(phone2);
entityManager.persist(person);
entityManager.flush();
person.getPhones().remove(phone1);
INSERT INTO Person
( id )
VALUES ( 1 )
INSERT INTO Phone
( number, id )
VALUES ( '123-456-7890', 2 )
INSERT INTO Phone
( number, id )
VALUES ( '321-654-0987', 3 )
INSERT INTO Person_Phone
( Person_id, phones_id )
VALUES ( 1, 2 )
INSERT INTO Person_Phone
( Person_id, phones_id )
VALUES ( 1, 3 )
DELETE FROM Person_Phone
WHERE Person_id = 1
INSERT INTO Person_Phone
( Person_id, phones_id )
VALUES ( 1, 3 )
DELETE FROM Phone
WHERE id = 2
When persisting the Person
entity, the cascade will propagate the persist operation to the underlying Phone
children as well.
Upon removing a Phone
from the phones collection, the association row is deleted from the link table, and the orphanRemoval
attribute will trigger a Phone
removal as well.
The unidirectional associations are not very efficient when it comes to removing child entities. On the other hand, a bidirectional |
Bidirectional @OneToMany
The bidirectional @OneToMany
association also requires a @ManyToOne
association on the child side.
Although the Domain Model exposes two sides to navigate this association, behind the scenes, the relational database has only one foreign key for this relationship.
Every bidirectional association must have one owning side only (the child side), the other one being referred to as the inverse (or the mappedBy
) side.
Example 192. @OneToMany
association mappedBy the @ManyToOne
side
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
phones.add(phone);
phone.setPerson(this);
}
public void removePhone(Phone phone) {
phones.remove(phone);
phone.setPerson(null);
}
}
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
@NaturalId
@Column(name = "`number`", unique = true)
private String number;
@ManyToOne
private Person person;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Phone phone = (Phone) o;
return Objects.equals(number, phone.number);
}
@Override
public int hashCode() {
return Objects.hash(number);
}
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
person_id BIGINT ,
PRIMARY KEY ( id )
)
ALTER TABLE Phone
ADD CONSTRAINT UK_l329ab0g4c1t78onljnxmbnp6
UNIQUE (number)
ALTER TABLE Phone
ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg
FOREIGN KEY (person_id) REFERENCES Person
Whenever a bidirectional association is formed, the application developer must make sure both sides are in-sync at all times. The |
Because the Phone
class has a @NaturalId
column (the phone number being unique),
the equals()
and the hashCode()
can make use of this property, and so the removePhone()
logic is reduced to the remove()
Java Collection
method.
Example 193. Bidirectional @OneToMany
with an owner @ManyToOne
side lifecycle
Person person = new Person();
Phone phone1 = new Phone("123-456-7890");
Phone phone2 = new Phone("321-654-0987");
person.addPhone(phone1);
person.addPhone(phone2);
entityManager.persist(person);
entityManager.flush();
person.removePhone(phone1);
INSERT INTO Person
( id )
VALUES ( 1 )
INSERT INTO Phone
( "number", person_id, id )
VALUES ( '123-456-7890', 1, 2 )
INSERT INTO Phone
( "number", person_id, id )
VALUES ( '321-654-0987', 1, 3 )
DELETE FROM Phone
WHERE id = 2
Unlike the unidirectional @OneToMany
, the bidirectional association is much more efficient when managing the collection persistence state.
Every element removal only requires a single update (in which the foreign key column is set to NULL
), and,
if the child entity lifecycle is bound to its owning parent so that the child cannot exist without its parent,
then we can annotate the association with the orphanRemoval
attribute and dissociating the child will trigger a delete statement on the actual child table row as well.
2.8.3. @OneToOne
The @OneToOne
association can either be unidirectional or bidirectional.
A unidirectional association follows the relational database foreign key semantics, the client-side owning the relationship.
A bidirectional association features a mappedBy
@OneToOne
parent side too.
Unidirectional @OneToOne
Example 194. Unidirectional @OneToOne
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
@Column(name = "`number`")
private String number;
@OneToOne
@JoinColumn(name = "details_id")
private PhoneDetails details;
//Getters and setters are omitted for brevity
}
@Entity(name = "PhoneDetails")
public static class PhoneDetails {
@Id
@GeneratedValue
private Long id;
private String provider;
private String technology;
//Getters and setters are omitted for brevity
}
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
details_id BIGINT ,
PRIMARY KEY ( id )
)
CREATE TABLE PhoneDetails (
id BIGINT NOT NULL ,
provider VARCHAR(255) ,
technology VARCHAR(255) ,
PRIMARY KEY ( id )
)
ALTER TABLE Phone
ADD CONSTRAINT FKnoj7cj83ppfqbnvqqa5kolub7
FOREIGN KEY (details_id) REFERENCES PhoneDetails
From a relational database point of view, the underlying schema is identical to the unidirectional @ManyToOne
association,
as the client-side controls the relationship based on the foreign key column.
But then, it’s unusual to consider the Phone
as a client-side and the PhoneDetails
as the parent-side because the details cannot exist without an actual phone.
A much more natural mapping would be the Phone
were the parent-side, therefore pushing the foreign key into the PhoneDetails
table.
This mapping requires a bidirectional @OneToOne
association as you can see in the following example:
Bidirectional @OneToOne
Example 195. Bidirectional @OneToOne
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
@Column(name = "`number`")
private String number;
@OneToOne(
mappedBy = "phone",
cascade = CascadeType.ALL,
orphanRemoval = true,
fetch = FetchType.LAZY
)
private PhoneDetails details;
//Getters and setters are omitted for brevity
public void addDetails(PhoneDetails details) {
details.setPhone(this);
this.details = details;
}
public void removeDetails() {
if (details != null) {
details.setPhone(null);
this.details = null;
}
}
}
@Entity(name = "PhoneDetails")
public static class PhoneDetails {
@Id
@GeneratedValue
private Long id;
private String provider;
private String technology;
@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "phone_id")
private Phone phone;
//Getters and setters are omitted for brevity
}
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE PhoneDetails (
id BIGINT NOT NULL ,
provider VARCHAR(255) ,
technology VARCHAR(255) ,
phone_id BIGINT ,
PRIMARY KEY ( id )
)
ALTER TABLE PhoneDetails
ADD CONSTRAINT FKeotuev8ja8v0sdh29dynqj05p
FOREIGN KEY (phone_id) REFERENCES Phone
This time, the PhoneDetails
owns the association, and, like any bidirectional association, the parent-side can propagate its lifecycle to the child-side through cascading.
Example 196. Bidirectional @OneToOne
lifecycle
Phone phone = new Phone("123-456-7890");
PhoneDetails details = new PhoneDetails("T-Mobile", "GSM");
phone.addDetails(details);
entityManager.persist(phone);
INSERT INTO Phone ( number, id )
VALUES ( '123-456-7890', 1 )
INSERT INTO PhoneDetails ( phone_id, provider, technology, id )
VALUES ( 1, 'T-Mobile', 'GSM', 2 )
When using a bidirectional @OneToOne
association, Hibernate enforces the unique constraint upon fetching the child-side.
If there are more than one children associated with the same parent, Hibernate will throw a org.hibernate.exception.ConstraintViolationException
.
Continuing the previous example, when adding another PhoneDetails
, Hibernate validates the uniqueness constraint when reloading the Phone
object.
Example 197. Bidirectional @OneToOne
unique constraint
PhoneDetails otherDetails = new PhoneDetails("T-Mobile", "CDMA");
otherDetails.setPhone(phone);
entityManager.persist(otherDetails);
entityManager.flush();
entityManager.clear();
//throws jakarta.persistence.PersistenceException: org.hibernate.HibernateException: More than one row with the given identifier was found: 1
phone = entityManager.find(Phone.class, phone.getId());
Bidirectional @OneToOne
lazy association
Although you might annotate the parent-side association to be fetched lazily,
Hibernate cannot honor this request since it cannot know whether the association is null
or not.
The only way to figure out whether there is an associated record on the child side is to fetch the child association using a secondary query.
Because this can lead to N+1 query issues, it’s much more efficient to use unidirectional @OneToOne
associations with the @MapsId
annotation in place.
However, if you really need to use a bidirectional association and want to make sure that this is always going to be fetched lazily,
then you need to enable lazy state initialization bytecode enhancement.
Example 198. Bidirectional @OneToOne
lazy parent-side association
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
@Column(name = "`number`")
private String number;
@OneToOne(
mappedBy = "phone",
cascade = CascadeType.ALL,
orphanRemoval = true,
fetch = FetchType.LAZY
)
private PhoneDetails details;
//Getters and setters are omitted for brevity
public void addDetails(PhoneDetails details) {
details.setPhone(this);
this.details = details;
}
public void removeDetails() {
if (details != null) {
details.setPhone(null);
this.details = null;
}
}
}
@Entity(name = "PhoneDetails")
public static class PhoneDetails {
@Id
@GeneratedValue
private Long id;
private String provider;
private String technology;
@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "phone_id")
private Phone phone;
//Getters and setters are omitted for brevity
}
For more about how to enable Bytecode enhancement,
see the Bytecode Enhancement chapter.
2.8.4. @ManyToMany
The @ManyToMany
association requires a link table that joins two entities.
Like the @OneToMany
association, @ManyToMany
can be either unidirectional or bidirectional.
Unidirectional @ManyToMany
Example 199. Unidirectional @ManyToMany
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private List<Address> addresses = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Address")
public static class Address {
@Id
@GeneratedValue
private Long id;
private String street;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
CREATE TABLE Address (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
street VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Person_Address (
Person_id BIGINT NOT NULL ,
addresses_id BIGINT NOT NULL
)
ALTER TABLE Person_Address
ADD CONSTRAINT FKm7j0bnabh2yr0pe99il1d066u
FOREIGN KEY (addresses_id) REFERENCES Address
ALTER TABLE Person_Address
ADD CONSTRAINT FKba7rc9qe2vh44u93u0p2auwti
FOREIGN KEY (Person_id) REFERENCES Person
Just like with unidirectional @OneToMany
associations, the link table is controlled by the owning side.
When an entity is removed from the @ManyToMany
collection, Hibernate simply deletes the joining record in the link table.
Unfortunately, this operation requires removing all entries associated with a given parent and recreating the ones that are listed in the current running persistent context.
Example 200. Unidirectional @ManyToMany
lifecycle
Person person1 = new Person();
Person person2 = new Person();
Address address1 = new Address("12th Avenue", "12A");
Address address2 = new Address("18th Avenue", "18B");
person1.getAddresses().add(address1);
person1.getAddresses().add(address2);
person2.getAddresses().add(address1);
entityManager.persist(person1);
entityManager.persist(person2);
entityManager.flush();
person1.getAddresses().remove(address1);
INSERT INTO Person ( id )
VALUES ( 1 )
INSERT INTO Address ( number, street, id )
VALUES ( '12A', '12th Avenue', 2 )
INSERT INTO Address ( number, street, id )
VALUES ( '18B', '18th Avenue', 3 )
INSERT INTO Person ( id )
VALUES ( 4 )
INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 1, 2 )
INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 1, 3 )
INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 4, 2 )
DELETE FROM Person_Address
WHERE Person_id = 1
INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 1, 3 )
For For example, if
|
By simply removing the parent-side, Hibernate can safely remove the associated link records as you can see in the following example:
Example 201. Unidirectional @ManyToMany
entity removal
Person person1 = entityManager.find(Person.class, personId);
entityManager.remove(person1);
DELETE FROM Person_Address
WHERE Person_id = 1
DELETE FROM Person
WHERE id = 1
Bidirectional @ManyToMany
A bidirectional @ManyToMany
association has an owning and a mappedBy
side.
To preserve synchronicity between both sides, it’s good practice to provide helper methods for adding or removing child entities.
Example 202. Bidirectional @ManyToMany
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@NaturalId
private String registrationNumber;
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private List<Address> addresses = new ArrayList<>();
//Getters and setters are omitted for brevity
public void addAddress(Address address) {
addresses.add(address);
address.getOwners().add(this);
}
public void removeAddress(Address address) {
addresses.remove(address);
address.getOwners().remove(this);
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Person person = (Person) o;
return Objects.equals(registrationNumber, person.registrationNumber);
}
@Override
public int hashCode() {
return Objects.hash(registrationNumber);
}
}
@Entity(name = "Address")
public static class Address {
@Id
@GeneratedValue
private Long id;
private String street;
@Column(name = "`number`")
private String number;
private String postalCode;
@ManyToMany(mappedBy = "addresses")
private List<Person> owners = new ArrayList<>();
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Address address = (Address) o;
return Objects.equals(street, address.street) &&
Objects.equals(number, address.number) &&
Objects.equals(postalCode, address.postalCode);
}
@Override
public int hashCode() {
return Objects.hash(street, number, postalCode);
}
}
CREATE TABLE Address (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
postalCode VARCHAR(255) ,
street VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE Person (
id BIGINT NOT NULL ,
registrationNumber VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE Person_Address (
owners_id BIGINT NOT NULL ,
addresses_id BIGINT NOT NULL
)
ALTER TABLE Person
ADD CONSTRAINT UK_23enodonj49jm8uwec4i7y37f
UNIQUE (registrationNumber)
ALTER TABLE Person_Address
ADD CONSTRAINT FKm7j0bnabh2yr0pe99il1d066u
FOREIGN KEY (addresses_id) REFERENCES Address
ALTER TABLE Person_Address
ADD CONSTRAINT FKbn86l24gmxdv2vmekayqcsgup
FOREIGN KEY (owners_id) REFERENCES Person
With the helper methods in place, the synchronicity management can be simplified, as you can see in the following example:
Example 203. Bidirectional @ManyToMany
lifecycle
Person person1 = new Person("ABC-123");
Person person2 = new Person("DEF-456");
Address address1 = new Address("12th Avenue", "12A", "4005A");
Address address2 = new Address("18th Avenue", "18B", "4007B");
person1.addAddress(address1);
person1.addAddress(address2);
person2.addAddress(address1);
entityManager.persist(person1);
entityManager.persist(person2);
entityManager.flush();
person1.removeAddress(address1);
INSERT INTO Person ( registrationNumber, id )
VALUES ( 'ABC-123', 1 )
INSERT INTO Address ( number, postalCode, street, id )
VALUES ( '12A', '4005A', '12th Avenue', 2 )
INSERT INTO Address ( number, postalCode, street, id )
VALUES ( '18B', '4007B', '18th Avenue', 3 )
INSERT INTO Person ( registrationNumber, id )
VALUES ( 'DEF-456', 4 )
INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 1, 2 )
INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 1, 3 )
INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 4, 2 )
DELETE FROM Person_Address
WHERE owners_id = 1
INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 1, 3 )
If a bidirectional @OneToMany
association performs better when removing or changing the order of child elements,
the @ManyToMany
relationship cannot benefit from such an optimization because the foreign key side is not in control.
To overcome this limitation, the link table must be directly exposed and the @ManyToMany
association split into two bidirectional @OneToMany
relationships.
Bidirectional many-to-many with a link entity
To most natural @ManyToMany
association follows the same logic employed by the database schema,
and the link table has an associated entity which controls the relationship for both sides that need to be joined.
Example 204. Bidirectional many-to-many with link entity
@Entity(name = "Person")
public static class Person implements Serializable {
@Id
@GeneratedValue
private Long id;
@NaturalId
private String registrationNumber;
@OneToMany(
mappedBy = "person",
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<PersonAddress> addresses = new ArrayList<>();
//Getters and setters are omitted for brevity
public void addAddress(Address address) {
PersonAddress personAddress = new PersonAddress(this, address);
addresses.add(personAddress);
address.getOwners().add(personAddress);
}
public void removeAddress(Address address) {
PersonAddress personAddress = new PersonAddress(this, address);
address.getOwners().remove(personAddress);
addresses.remove(personAddress);
personAddress.setPerson(null);
personAddress.setAddress(null);
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Person person = (Person) o;
return Objects.equals(registrationNumber, person.registrationNumber);
}
@Override
public int hashCode() {
return Objects.hash(registrationNumber);
}
}
@Entity(name = "PersonAddress")
public static class PersonAddress implements Serializable {
@Id
@ManyToOne
private Person person;
@Id
@ManyToOne
private Address address;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
PersonAddress that = (PersonAddress) o;
return Objects.equals(person, that.person) &&
Objects.equals(address, that.address);
}
@Override
public int hashCode() {
return Objects.hash(person, address);
}
}
@Entity(name = "Address")
public static class Address implements Serializable {
@Id
@GeneratedValue
private Long id;
private String street;
@Column(name = "`number`")
private String number;
private String postalCode;
@OneToMany(
mappedBy = "address",
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<PersonAddress> owners = new ArrayList<>();
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Address address = (Address) o;
return Objects.equals(street, address.street) &&
Objects.equals(number, address.number) &&
Objects.equals(postalCode, address.postalCode);
}
@Override
public int hashCode() {
return Objects.hash(street, number, postalCode);
}
}
CREATE TABLE Address (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
postalCode VARCHAR(255) ,
street VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE Person (
id BIGINT NOT NULL ,
registrationNumber VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE PersonAddress (
person_id BIGINT NOT NULL ,
address_id BIGINT NOT NULL ,
PRIMARY KEY ( person_id, address_id )
)
ALTER TABLE Person
ADD CONSTRAINT UK_23enodonj49jm8uwec4i7y37f
UNIQUE (registrationNumber)
ALTER TABLE PersonAddress
ADD CONSTRAINT FK8b3lru5fyej1aarjflamwghqq
FOREIGN KEY (person_id) REFERENCES Person
ALTER TABLE PersonAddress
ADD CONSTRAINT FK7p69mgialumhegyl4byrh65jk
FOREIGN KEY (address_id) REFERENCES Address
Both the Person
and the Address
have a mappedBy
@OneToMany
side, while the PersonAddress
owns the person
and the address
@ManyToOne
associations.
Because this mapping is formed out of two bidirectional associations, the helper methods are even more relevant.
The aforementioned example uses a Hibernate-specific mapping for the link entity since Jakarta Persistence doesn’t allow building a composite identifier out of multiple For more details, see the composite identifiers with associations section. |
The entity state transitions are better managed than in the previous bidirectional @ManyToMany
case.
Example 205. Bidirectional many-to-many with link entity lifecycle
Person person1 = new Person("ABC-123");
Person person2 = new Person("DEF-456");
Address address1 = new Address("12th Avenue", "12A", "4005A");
Address address2 = new Address("18th Avenue", "18B", "4007B");
entityManager.persist(person1);
entityManager.persist(person2);
entityManager.persist(address1);
entityManager.persist(address2);
person1.addAddress(address1);
person1.addAddress(address2);
person2.addAddress(address1);
entityManager.flush();
log.info("Removing address");
person1.removeAddress(address1);
INSERT INTO Person ( registrationNumber, id )
VALUES ( 'ABC-123', 1 )
INSERT INTO Person ( registrationNumber, id )
VALUES ( 'DEF-456', 2 )
INSERT INTO Address ( number, postalCode, street, id )
VALUES ( '12A', '4005A', '12th Avenue', 3 )
INSERT INTO Address ( number, postalCode, street, id )
VALUES ( '18B', '4007B', '18th Avenue', 4 )
INSERT INTO PersonAddress ( person_id, address_id )
VALUES ( 1, 3 )
INSERT INTO PersonAddress ( person_id, address_id )
VALUES ( 1, 4 )
INSERT INTO PersonAddress ( person_id, address_id )
VALUES ( 2, 3 )
DELETE FROM PersonAddress
WHERE person_id = 1 AND address_id = 3
There is only one delete statement executed because, this time, the association is controlled by the @ManyToOne
side which only has to monitor the state of the underlying foreign key relationship to trigger the right DML statement.
2.8.5. @NotFound
When dealing with associations which are not enforced by a physical foreign-key, it is possible
for a non-null foreign-key value to point to a non-existent value on the associated entity’s table.
Not enforcing physical foreign-keys at the database level is highly discouraged. |
Hibernate provides support for such models using the @NotFound
annotation, which accepts a
NotFoundAction
value which indicates how Hibernate should behave when such broken foreign-keys
are encountered —
- EXCEPTION
-
(default) Hibernate will throw an exception (
FetchNotFoundException
) - IGNORE
-
the association will be treated as
null
Both @NotFound(IGNORE)
and @NotFound(EXCEPTION)
cause Hibernate to assume that there is
no physical foreign-key.
@ManyToOne
and @OneToOne
associations annotated with @NotFound
are always fetched eagerly even
if the fetch
strategy is set to FetchType.LAZY
.
If the application itself manages the referential integrity and can guarantee that there are no |
Considering the following City
and Person
entity mappings:
Example 206. @NotFound
mapping example
@Entity(name = "Person")
@Table(name = "Person")
public static class Person {
@Id
private Integer id;
private String name;
@ManyToOne
@NotFound(action = NotFoundAction.IGNORE)
@JoinColumn(name = "city_fk", referencedColumnName = "id")
private City city;
//Getters and setters are omitted for brevity
}
@Entity(name = "City")
@Table(name = "City")
public static class City implements Serializable {
@Id
private Integer id;
private String name;
//Getters and setters are omitted for brevity
}
If we have the following entities in our database:
Example 207. @NotFound
persist example
City newYork = new City( 1, "New York" );
entityManager.persist( newYork );
Person person = new Person( 1, "John Doe", newYork );
entityManager.persist( person );
When loading the Person
entity, Hibernate is able to locate the associated City
parent entity:
Example 208. @NotFound
— find existing entity example
Person person = entityManager.find( Person.class, 1 );
assertEquals( "New York", person.getCity().getName() );
However, if we break the foreign-key:
Example 209. Break the foreign-key
// the database allows this because there is no physical foreign-key
entityManager.createQuery( "delete City" ).executeUpdate();
Hibernate is not going to throw any exception, and it will assign a value of null
for the non-existing City
entity reference:
Example 210. @NotFound
— find non-existing City example
Person person = entityManager.find( Person.class, 1 );
assertNull( person.getCity(), "person.getCity() should be null" );
@NotFound
also affects how the association is treated as «implicit joins» in HQL and Criteria.
When there is a physical foreign-key, Hibernate can safely assume that the value in the foreign-key’s
key-column(s) will match the value in the target-column(s) because the database makes sure that
is the case. However, @NotFound
forces Hibernate to perform a physical join for implicit joins
when it might not be needed otherwise.
Using the Person
/ City
model, consider the query from Person p where p.city.id is null
.
Normally Hibernate would not need the join between the Person
table and the City
table because
a physical foreign-key would ensure that any non-null value in the Person.cityName
column
has a matching non-null value in the City.name
column.
However, with @NotFound
mappings it is possible to have a broken association because there is no
physical foreign-key enforcing the relation. As seen in Break the foreign-key,
the Person.cityName
column for John Doe has been changed from «New York» to «Atlantis» even though
there is no City
in the database named «Atlantis». Hibernate is not able to trust the referring
foreign-key value («Atlantis») has a matching target value, so it must join to the City
table to
resolve the city.id
value.
Example 211. Implicit join example
final List<Person> nullResults = entityManager
.createQuery( "from Person p where p.city.id is null", Person.class )
.getResultList();
assertThat( nullResults ).isEmpty();
final List<Person> nonNullResults = entityManager
.createQuery( "from Person p where p.city.id is not null", Person.class )
.getResultList();
assertThat( nonNullResults ).isEmpty();
Neither result includes a match for «John Doe» because the inner-join filters out that row.
Hibernate does support a means to refer specifically to the key column (Person.cityName
) in a query
using the special fk(..)
function. E.g.
Example 212. Implicit join example
final List<String> nullResults = entityManager
.createQuery( "select p.name from Person p where fk( p.city ) is null", String.class )
.getResultList();
assertThat( nullResults ).isEmpty();
final List<String> nonNullResults = entityManager
.createQuery( "select p.name from Person p where fk( p.city ) is not null", String.class )
.getResultList();
assertThat( nonNullResults ).hasSize( 1 );
assertThat( nonNullResults.get( 0 ) ).isEqualTo( "John Doe" );
See [hql-model-functions].
2.8.6. @Any
mapping
The @Any
mapping is useful to emulate a unidirectional @ManyToOne
association when there can be multiple target entities.
Because the @Any
mapping defines a polymorphic association to classes from multiple tables,
this association type requires the FK column which provides the associated parent identifier and
a metadata information for the associated entity type.
This is not the usual way of mapping polymorphic associations and you should use this only in special cases (e.g. audit logs, user session data, etc). |
To map such an association, Hibernate needs to understand 3 things:
-
The column and mapping for the discriminator
-
The column and mapping for the key
-
The mapping between discriminator values and entity classes
The discriminator
The discriminator of an any-style association holds the value that indicates which entity is
referred to by a row.
Its «column» can be specified with either @Column
or @Formula
. The mapping type can be influenced by any of:
-
@AnyDiscriminator
allows re-using theDiscriminatorType
simplified mappings from Jakarta Persistence for the common cases -
@JavaType
-
@JdbcType
-
@JdbcTypeCode
The key
The key of an any-style association holds the matching key for the row
Its «column» can be specified with either @JoinColumn
(@JoinFormula
not supported). The mapping
type can be influenced by any of:
-
@AnyKeyJavaClass
-
@AnyKeyJavaType
-
@AnyKeyJdbcType
-
@AnyKeyJdbcTypeCode
The discriminator value mappings
@AnyDiscriminatorValue
is used to map the discriminator values to the corresponding entity classes
2.8.7. Example using @Any mapping
For this example, consider the following Property
class hierarchy:
Example 213. Property
class hierarchy
public interface Property<T> {
String getName();
T getValue();
}
@Entity
@Table(name="integer_property")
public class IntegerProperty implements Property<Integer> {
@Id
private Long id;
@Column(name = "`name`")
private String name;
@Column(name = "`value`")
private Integer value;
@Override
public String getName() {
return name;
}
@Override
public Integer getValue() {
return value;
}
//Getters and setters omitted for brevity
}
@Entity
@Table(name="string_property")
public class StringProperty implements Property<String> {
@Id
private Long id;
@Column(name = "`name`")
private String name;
@Column(name = "`value`")
private String value;
@Override
public String getName() {
return name;
}
@Override
public String getValue() {
return value;
}
//Getters and setters omitted for brevity
}
A PropertyHolder
entity defines an attribute of type Property
:
Example 214. @Any
mapping usage
@Entity
@Table(name = "property_holder")
public class PropertyHolder {
@Id
private Long id;
@Any
@AnyDiscriminator(DiscriminatorType.STRING)
@AnyDiscriminatorValue(discriminator = "S", entity = StringProperty.class)
@AnyDiscriminatorValue(discriminator = "I", entity = IntegerProperty.class)
@AnyKeyJavaClass(Long.class)
@Column(name = "property_type")
@JoinColumn(name = "property_id")
private Property property;
//Getters and setters are omitted for brevity
}
CREATE TABLE property_holder (
id BIGINT NOT NULL,
property_type VARCHAR(255),
property_id BIGINT,
PRIMARY KEY ( id )
)
PropertyHolder#property
can refer to either StringProperty
or IntegerProperty
references, as indicated
by the associated discriminator according to the @DiscriminatorValue
annotations.
As you can see, there are two columns used to reference a Property
instance: property_id
and property_type
.
The property_id
is used to match the id
column of either the string_property
or integer_property
tables,
while the property_type
is used to match the string_property
or the integer_property
table.
To see the @Any
annotation in action, consider the next examples.
If we persist an IntegerProperty
as well as a StringProperty
entity, and associate
the StringProperty
entity with a PropertyHolder
,
Hibernate will generate the following SQL queries:
Example 215. @Any
mapping persist example
IntegerProperty ageProperty = new IntegerProperty();
ageProperty.setId(1L);
ageProperty.setName("age");
ageProperty.setValue(23);
session.persist(ageProperty);
StringProperty nameProperty = new StringProperty();
nameProperty.setId(1L);
nameProperty.setName("name");
nameProperty.setValue("John Doe");
session.persist(nameProperty);
PropertyHolder namePropertyHolder = new PropertyHolder();
namePropertyHolder.setId(1L);
namePropertyHolder.setProperty(nameProperty);
session.persist(namePropertyHolder);
INSERT INTO integer_property
( "name", "value", id )
VALUES ( 'age', 23, 1 )
INSERT INTO string_property
( "name", "value", id )
VALUES ( 'name', 'John Doe', 1 )
INSERT INTO property_holder
( property_type, property_id, id )
VALUES ( 'S', 1, 1 )
When fetching the PropertyHolder
entity and navigating its property
association,
Hibernate will fetch the associated StringProperty
entity like this:
Example 216. @Any
mapping query example
PropertyHolder propertyHolder = session.get(PropertyHolder.class, 1L);
assertEquals("name", propertyHolder.getProperty().getName());
assertEquals("John Doe", propertyHolder.getProperty().getValue());
SELECT ph.id AS id1_1_0_,
ph.property_type AS property2_1_0_,
ph.property_id AS property3_1_0_
FROM property_holder ph
WHERE ph.id = 1
SELECT sp.id AS id1_2_0_,
sp."name" AS name2_2_0_,
sp."value" AS value3_2_0_
FROM string_property sp
WHERE sp.id = 1
Using meta-annotations
As mentioned in Mapping basic values, Hibernate’s ANY-related annotations can be composed using meta-annotations
to re-use ANY mapping details.
Looking back at @Any
mapping usage, we can see how cumbersome it would be to duplicate that
information every time Property
is mapped in the domain model. This description can also be moved
into a single annotation that we can apply in each usage.
Example 217. @Any
mapping usage
@Entity
@Table(name = "property_holder2")
public class PropertyHolder2 {
@Id
private Long id;
@Any
@PropertyDiscriminationDef
@Column(name = "property_type")
@JoinColumn(name = "property_id")
private Property property;
//Getters and setters are omitted for brevity
}
Though the mapping has been «simplified», the mapping works exactly as shown in @Any
mapping usage.
@ManyToAny
mapping
While the @Any
mapping is useful to emulate a @ManyToOne
association when there can be multiple target entities,
to emulate a @OneToMany
association, the @ManyToAny
annotation must be used.
The mapping details are the same between @Any
and @ManyToAny
except for:
-
The use of
@ManyToAny
instead of@Any
-
The use of
@JoinTable
,@JoinTable#joinColumns
and@JoinTable#inverseJoinColumns
instead
of just@JoinColumn
In the following example, the PropertyRepository
entity has a collection of Property
entities.
The repository_properties
link table holds the associations between PropertyRepository
and Property
entities.
Example 218. @ManyToAny
mapping usage
@Entity
@Table(name = "property_repository")
public class PropertyRepository {
@Id
private Long id;
@ManyToAny
@AnyDiscriminator(DiscriminatorType.STRING)
@Column(name = "property_type")
@AnyKeyJavaClass(Long.class)
@AnyDiscriminatorValue(discriminator = "S", entity = StringProperty.class)
@AnyDiscriminatorValue(discriminator = "I", entity = IntegerProperty.class)
@Cascade(ALL)
@JoinTable(name = "repository_properties",
joinColumns = @JoinColumn(name = "repository_id"),
inverseJoinColumns = @JoinColumn(name = "property_id")
)
private List<Property<?>> properties = new ArrayList<>();
//Getters and setters are omitted for brevity
}
CREATE TABLE property_repository (
id BIGINT NOT NULL,
PRIMARY KEY ( id )
)
CREATE TABLE repository_properties (
repository_id BIGINT NOT NULL,
property_type VARCHAR(255),
property_id BIGINT NOT NULL
)
To see the @ManyToAny
annotation in action, consider the next examples.
If we persist an IntegerProperty
as well as a StringProperty
entity,
and associate both of them with a PropertyRepository
parent entity,
Hibernate will generate the following SQL queries:
Example 219. @ManyToAny
mapping persist example
IntegerProperty ageProperty = new IntegerProperty();
ageProperty.setId(1L);
ageProperty.setName("age");
ageProperty.setValue(23);
session.persist(ageProperty);
StringProperty nameProperty = new StringProperty();
nameProperty.setId(1L);
nameProperty.setName("name");
nameProperty.setValue("John Doe");
session.persist(nameProperty);
PropertyRepository propertyRepository = new PropertyRepository();
propertyRepository.setId(1L);
propertyRepository.getProperties().add(ageProperty);
propertyRepository.getProperties().add(nameProperty);
session.persist(propertyRepository);
INSERT INTO integer_property
( "name", "value", id )
VALUES ( 'age', 23, 1 )
INSERT INTO string_property
( "name", "value", id )
VALUES ( 'name', 'John Doe', 1 )
INSERT INTO property_repository ( id )
VALUES ( 1 )
INSERT INTO repository_properties
( repository_id , property_type , property_id )
VALUES
( 1 , 'I' , 1 )
When fetching the PropertyRepository
entity and navigating its properties
association,
Hibernate will fetch the associated IntegerProperty
and StringProperty
entities like this:
Example 220. @ManyToAny
mapping query example
PropertyRepository propertyRepository = session.get(PropertyRepository.class, 1L);
assertEquals(2, propertyRepository.getProperties().size());
for(Property property : propertyRepository.getProperties()) {
assertNotNull(property.getValue());
}
SELECT pr.id AS id1_1_0_
FROM property_repository pr
WHERE pr.id = 1
SELECT ip.id AS id1_0_0_ ,
ip."name" AS name2_0_0_ ,
ip."value" AS value3_0_0_
FROM integer_property ip
WHERE ip.id = 1
SELECT sp.id AS id1_3_0_ ,
sp."name" AS name2_3_0_ ,
sp."value" AS value3_3_0_
FROM string_property sp
WHERE sp.id = 1
2.8.8. @JoinFormula
mapping
The @JoinFormula
annotation is used to customize the join between a child Foreign Key and a parent row Primary Key.
Example 221. @JoinFormula
mapping usage
@Entity(name = "User")
@Table(name = "users")
public static class User {
@Id
private Long id;
private String firstName;
private String lastName;
private String phoneNumber;
@ManyToOne
@JoinFormula("REGEXP_REPLACE(phoneNumber, '\\+(\\d+)-.*', '\\1')::int")
private Country country;
//Getters and setters omitted for brevity
}
@Entity(name = "Country")
@Table(name = "countries")
public static class Country {
@Id
private Integer id;
private String name;
//Getters and setters, equals and hashCode methods omitted for brevity
}
CREATE TABLE countries (
id int4 NOT NULL,
name VARCHAR(255),
PRIMARY KEY ( id )
)
CREATE TABLE users (
id int8 NOT NULL,
firstName VARCHAR(255),
lastName VARCHAR(255),
phoneNumber VARCHAR(255),
PRIMARY KEY ( id )
)
The country
association in the User
entity is mapped by the country identifier provided by the phoneNumber
property.
Considering we have the following entities:
Example 222. @JoinFormula
mapping usage
Country US = new Country();
US.setId(1);
US.setName("United States");
Country Romania = new Country();
Romania.setId(40);
Romania.setName("Romania");
doInJPA(this::entityManagerFactory, entityManager -> {
entityManager.persist(US);
entityManager.persist(Romania);
});
doInJPA(this::entityManagerFactory, entityManager -> {
User user1 = new User();
user1.setId(1L);
user1.setFirstName("John");
user1.setLastName("Doe");
user1.setPhoneNumber("+1-234-5678");
entityManager.persist(user1);
User user2 = new User();
user2.setId(2L);
user2.setFirstName("Vlad");
user2.setLastName("Mihalcea");
user2.setPhoneNumber("+40-123-4567");
entityManager.persist(user2);
});
When fetching the User
entities, the country
property is mapped by the @JoinFormula
expression:
Example 223. @JoinFormula
mapping usage
doInJPA(this::entityManagerFactory, entityManager -> {
log.info("Fetch User entities");
User john = entityManager.find(User.class, 1L);
assertEquals(US, john.getCountry());
User vlad = entityManager.find(User.class, 2L);
assertEquals(Romania, vlad.getCountry());
});
-- Fetch User entities
SELECT
u.id as id1_1_0_,
u.firstName as firstNam2_1_0_,
u.lastName as lastName3_1_0_,
u.phoneNumber as phoneNum4_1_0_,
REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int as formula1_0_,
c.id as id1_0_1_,
c.name as name2_0_1_
FROM
users u
LEFT OUTER JOIN
countries c
ON REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int = c.id
WHERE
u.id=?
-- binding parameter [1] as [BIGINT] - [1]
SELECT
u.id as id1_1_0_,
u.firstName as firstNam2_1_0_,
u.lastName as lastName3_1_0_,
u.phoneNumber as phoneNum4_1_0_,
REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int as formula1_0_,
c.id as id1_0_1_,
c.name as name2_0_1_
FROM
users u
LEFT OUTER JOIN
countries c
ON REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int = c.id
WHERE
u.id=?
-- binding parameter [1] as [BIGINT] - [2]
Therefore, the @JoinFormula
annotation is used to define a custom join association between the parent-child association.
2.8.9. @JoinColumnOrFormula
mapping
The @JoinColumnOrFormula
annotation is used to customize the join between a child Foreign Key and a parent row Primary Key when we need to take into consideration a column value as well as a @JoinFormula
.
Example 224. @JoinColumnOrFormula
mapping usage
@Entity(name = "User")
@Table(name = "users")
public static class User {
@Id
private Long id;
private String firstName;
private String lastName;
private String language;
@ManyToOne
@JoinColumnOrFormula(column =
@JoinColumn(
name = "language",
referencedColumnName = "primaryLanguage",
insertable = false,
updatable = false
)
)
@JoinColumnOrFormula(formula =
@JoinFormula(
value = "true",
referencedColumnName = "is_default"
)
)
private Country country;
//Getters and setters omitted for brevity
}
@Entity(name = "Country")
@Table(name = "countries")
public static class Country implements Serializable {
@Id
private Integer id;
private String name;
private String primaryLanguage;
@Column(name = "is_default")
private boolean _default;
//Getters and setters, equals and hashCode methods omitted for brevity
}
CREATE TABLE countries (
id INTEGER NOT NULL,
is_default boolean,
name VARCHAR(255),
primaryLanguage VARCHAR(255),
PRIMARY KEY ( id )
)
CREATE TABLE users (
id BIGINT NOT NULL,
firstName VARCHAR(255),
language VARCHAR(255),
lastName VARCHAR(255),
PRIMARY KEY ( id )
)
The country
association in the User
entity is mapped by the language
property value and the associated Country
is_default
column value.
Considering we have the following entities:
Example 225. @JoinColumnOrFormula
persist example
Country US = new Country();
US.setId(1);
US.setDefault(true);
US.setPrimaryLanguage("English");
US.setName("United States");
Country Romania = new Country();
Romania.setId(40);
Romania.setDefault(true);
Romania.setName("Romania");
Romania.setPrimaryLanguage("Romanian");
doInJPA(this::entityManagerFactory, entityManager -> {
entityManager.persist(US);
entityManager.persist(Romania);
});
doInJPA(this::entityManagerFactory, entityManager -> {
User user1 = new User();
user1.setId(1L);
user1.setFirstName("John");
user1.setLastName("Doe");
user1.setLanguage("English");
entityManager.persist(user1);
User user2 = new User();
user2.setId(2L);
user2.setFirstName("Vlad");
user2.setLastName("Mihalcea");
user2.setLanguage("Romanian");
entityManager.persist(user2);
});
When fetching the User
entities, the country
property is mapped by the @JoinColumnOrFormula
expression:
Example 226. @JoinColumnOrFormula
fetching example
doInJPA(this::entityManagerFactory, entityManager -> {
log.info("Fetch User entities");
User john = entityManager.find(User.class, 1L);
assertEquals(US, john.getCountry());
User vlad = entityManager.find(User.class, 2L);
assertEquals(Romania, vlad.getCountry());
});
SELECT
u.id as id1_1_0_,
u.language as language3_1_0_,
u.firstName as firstNam2_1_0_,
u.lastName as lastName4_1_0_,
1 as formula1_0_,
c.id as id1_0_1_,
c.is_default as is_defau2_0_1_,
c.name as name3_0_1_,
c.primaryLanguage as primaryL4_0_1_
FROM
users u
LEFT OUTER JOIN
countries c
ON u.language = c.primaryLanguage
AND 1 = c.is_default
WHERE
u.id = ?
-- binding parameter [1] as [BIGINT] - [1]
SELECT
u.id as id1_1_0_,
u.language as language3_1_0_,
u.firstName as firstNam2_1_0_,
u.lastName as lastName4_1_0_,
1 as formula1_0_,
c.id as id1_0_1_,
c.is_default as is_defau2_0_1_,
c.name as name3_0_1_,
c.primaryLanguage as primaryL4_0_1_
FROM
users u
LEFT OUTER JOIN
countries c
ON u.language = c.primaryLanguage
AND 1 = c.is_default
WHERE
u.id = ?
-- binding parameter [1] as [BIGINT] - [2]
Therefore, the @JoinColumnOrFormula
annotation is used to define a custom join association between the parent-child association.
2.9. Collections
Hibernate supports mapping collections (java.util.Collection
and java.util.Map
subtypes)
in a variety of ways.
Hibernate even allows mapping a collection as @Basic
, but that should generally be avoided.
See Collections as basic value type for details of such a mapping.
This section is limited to discussing @ElementCollection
, @OneToMany
and @ManyToMany
.
Two entities cannot share a reference to the same collection instance. Collection-valued properties do not support null value semantics. Collections cannot be nested, meaning Hibernate does not support mapping Embeddables which are used as a collection element, Map value or Map key may not themselves define collections |
2.9.1. Collection Semantics
The semantics of a collection describes how to handle the collection, including
-
the collection subtype to use —
java.util.List
,java.util.Set
,java.util.SortedSet
, etc. -
how to access elements of the collection
-
how to create instances of the collection — both «raw» and «wrapper» forms.
Hibernate supports the following semantics:
- ARRAY
-
Object and primitive arrays. See Mapping Arrays.
- BAG
-
A collection that may contain duplicate entries and has no defined ordering. See Mapping Collections.
- ID_BAG
-
A bag that defines a per-element identifier to uniquely identify elements in the collection. See Mapping Collections.
- LIST
-
Follows the semantics defined by
java.util.List
. See Ordered Lists. - SET
-
Follows the semantics defined by
java.util.Set
. See Mapping Sets. - ORDERED_SET
-
A set that is ordered by a SQL fragment defined on its mapping. See Mapping Sets.
- SORTED_SET
-
A set that is sorted according to a
Comparator
defined on its mapping. See Mapping Sets. - MAP
-
Follows the semantics defined by
java.util.Map
. See Mapping Maps. - ORDERED_MAP
-
A map that is ordered by keys according to a SQL fragment defined on its mapping. See Mapping Maps.
- SORTED_MAP
-
A map that is sorted by keys according to a
Comparator
defined on its mapping. See Mapping Maps.
By default, Hibernate interprets the defined type of the plural attribute and makes an
interpretation as to which classification it fits in to, using the following checks:
-
if an array → ARRAY
-
if a
List
→ LIST -
if a
SortedSet
→ SORTED_SET -
if a
Set
→ SET -
if a
SortedMap
→ SORTED_MAP -
if a
Map
→ MAP -
else
Collection
→ BAG
2.9.2. Mapping Lists
java.util.List
defines a collection of ordered, non-unique elements.
Example 227. Basic List Mapping
@Entity
public class EntityWithList {
// ...
@ElementCollection
private List<Name> names;
}
Contrary to natural expectations, the ordering of a list is by default not maintained.
To maintain the order, it is necessary to explicitly use the jakarta.persistence.OrderColumn
annotation.
Starting in 6.0, Hibernate allows to configure the default semantics of List
without @OrderColumn
via the hibernate.mapping.default_list_semantics
setting.
To switch to the more natural LIST semantics with an implicit order-column, set the setting to LIST
.
Beware that default LIST semantics only affects owned collection mappings.
Unowned mappings like @ManyToMany(mappedBy = "…")
and @OneToMany(mappedBy = "…")
do not retain the element
order by default, and explicitly annotating @OrderColumn
for @ManyToMany(mappedBy = "…")
mappings is illegal.
To retain the order of elements of a @OneToMany(mappedBy = "…")
the @OrderColumn
annotation must be applied
explicitly. In addition to that, it is important that both sides of the relationship, the @OneToMany(mappedBy = "…")
and the @ManyToOne
, must be kept in sync. Otherwise, the element position will not be updated accordingly.
The default column name that stores the index is derived from the attribute name, by suffixing _ORDER
.
Example 228. @OrderColumn
@Entity
public class EntityWithOrderColumnList {
// ...
@ElementCollection
@OrderColumn( name = "name_index" )
private List<Name> names;
}
Now, a column named name_index
will be used.
Hibernate stores index values into the order-column based on the element’s position in the list
with no adjustment. The element at names[0]
is stored with name_index=0
and so on. That is to say
that the list index is considered 0-based just as list indexes themselves are 0-based. Some legacy
schemas might map the position as 1-based, or any base really. Hibernate also defines support for such
cases using its @ListIndexBase
annotation.
Example 229. @ListIndexBase
@Entity
public class EntityWithIndexBasedList {
// ...
@ElementCollection
@OrderColumn(name = "name_index")
@ListIndexBase(1)
private List<Name> names;
}
2.9.3. Mapping Sets
java.util.Set
defines a collection of unique, though unordered elements. Hibernate supports
mapping sets according to the requirements of the java.util.Set
.
Example 230. Basic Set Mapping
@Entity
public class EntityWithSet {
// ...
@ElementCollection
private Set<Name> names;
}
Hibernate also has the ability to map sorted and ordered sets. A sorted set orders its
elements in memory via an associated Comparator
; an ordered set is ordered via
SQL when the set is loaded.
- TIP
-
An ordered set does not perform any sorting in-memory. If an element is added
after the collection is loaded, the collection would need to be refreshed to re-order
the elements. For this reason, ordered sets are not recommended — if the application
needs ordering of the set elements, a sorted set should be preferred. For this reason,
it is not covered in the User Guide. See the javadocs forjakarta.persistence.OrderBy
ororg.hibernate.annotations.OrderBy
for details.
There are 2 options for sorting a set — naturally or using an explicit comparator.
A set is naturally sorted using the natural sort comparator for its elements. Generally
this implies that the element type is Comparable
. E.g.
Example 231. @SortNatural
@Embeddable
@Access( AccessType.FIELD )
public class Name implements Comparable<Name> {
private String first;
private String last;
// ...
}
@Entity
public class EntityWithNaturallySortedSet {
// ...
@ElementCollection
@SortNatural
private SortedSet<Name> names;
}
Because Name
is defined as Comparable
, its #compare
method will be used to sort the elements in this
set.
But Hibernate also allows sorting based on a specific Comparator
implementation. Here, e.g., we map
the Names
as sorted by a NameComparator
:
Example 232. @SortComparator
public class NameComparator implements Comparator<Name> {
static final Comparator<Name> comparator = Comparator.comparing( Name::getLast ).thenComparing( Name::getFirst );
@Override
public int compare(Name o1, Name o2) {
return comparator.compare( o1, o2 );
}
}
@Entity
public class EntityWithSortedSet {
// ...
@ElementCollection
@SortComparator( NameComparator.class )
private SortedSet<Name> names;
}
Here, instead of Name#compare
being use for the sorting, the explicit NameComparator
will be used
instead.
2.9.4. Mapping Maps
A java.util.Map
is a collection of key/value pairs.
Example 233. Simple MAP mapping
@Entity
public class EntityWithMap {
// ...
@ElementCollection
private Map<Name, Status> names;
}
Hibernate has the ability to map sorted and ordered maps — the ordering and sorting applies
to the Map key. As we saw with Sets, the use of ordered Maps is generally discouraged.
Maps may be sorted naturally —
Example 234. Naturally sorted MAP mapping
@Entity
public class EntityWithNaturallySortedMap {
// ...
@ElementCollection
@SortNatural
private Map<Name, Status> names;
}
or via a Comparator —
Example 235. Comparator sorted MAP mapping
@Entity
public class EntityWithSortedMap {
// ...
@ElementCollection
@SortComparator( NameComparator.class )
private Map<Name, Status> names;
}
2.9.5. Mapping Collections
Without any other mapping influencers, java.util.Collection
is interpreted using BAG
semantics which means a collection that may contain duplicate entries and has no defined
ordering.
Jakarta Persistence does not define support for BAG (nor ID_BAG) classification per-se. The |
Example 236. Simple BAG mapping
@Entity
public class EntityWithBagAsCollection {
// ..
@ElementCollection
private Collection<Name> names;
}
Some apps map BAG collections using java.util.List
instead. Hibernate provides 2 ways to handle
lists as bags. First an explicit annotation
Example 237. @Bag
@Entity
public class EntityWithBagAsList {
// ..
@ElementCollection
@Bag
private List<Name> names;
}
Specifically, the usage of @Bag
forces the classification as BAG. Even though the names
attribute is defined
as List
, Hibernate will treat it using the BAG semantics.
Additionally, as discussed in Mapping Lists, the hibernate.mapping.default_list_semantics
setting
is available to have Hibernate interpret a List
with no @OrderColumn
and no @ListIndexBase
as a BAG.
An ID_BAG is similar to a BAG, except that it maps a generated, per-row identifier into the collection
table. @CollectionId
is the annotation to configure this identifier
2.9.6. Mapping Arrays
Hibernate is able to map Object and primitive arrays as collections. Mapping an array is essentially
the same as mapping a list.
There is a major limitation of mapping arrays to be aware of — the array cannot be lazy using
wrappers. It can, however, be lazy via bytecode enhancement
of its owner.
Note that Jakarta Persistence does not define support for arrays as plural attributes; according to the specification,
these would be mapped as binary data.
2.9.7. @ElementCollection
Element collections may contain values of either basic or embeddable types. They have a similar
lifecycle to basic/embedded attributes in that their persistence is completely managed as part of
the owner — they are created when referenced from an owner and automatically deleted when
unreferenced. The specifics of how this lifecycle manifests in terms of database calls depends
on the semantics of the mapping.
This section will discuss these lifecycle aspects using the example of mapping a collection
of phone numbers. The examples use embeddable values, but the same aspects apply to collections
of basic values as well.
The embeddable used in the examples is a PhoneNumber
—
Example 238. PhoneNumber
@Embeddable
public class Phone {
private String type;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
First, a BAG mapping —
Example 239. Elemental BAG mapping
@Entity(name = "Person")
public static class Person {
@Id
private Integer id;
@ElementCollection
private Collection<String> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
Example 240. Elemental BAG lifecycle
// Clear element collection and add element
person.getPhones().clear();
person.getPhones().add( "123-456-7890" );
person.getPhones().add( "456-000-1234" );
delete from Person_phones where Person_id=1
INSERT INTO Person_phones ( Person_id, phones )
VALUES ( 1, '123-456-7890' )
INSERT INTO Person_phones (Person_id, phones)
VALUES ( 1, '456-000-1234' )
Collections of entities
If value type collections can only form a one-to-many association between an owner entity and multiple basic or embeddable types,
entity collections can represent both @OneToMany and @ManyToMany associations.
From a relational database perspective, associations are defined by the foreign key side (the child-side).
With value type collections, only the entity can control the association (the parent-side), but for a collection of entities, both sides of the association are managed by the persistence context.
For this reason, entity collections can be devised into two main categories: unidirectional and bidirectional associations.
Unidirectional associations are very similar to value type collections since only the parent side controls this relationship.
Bidirectional associations are more tricky since, even if sides need to be in-sync at all times, only one side is responsible for managing the association.
A bidirectional association has an owning side and an inverse (mappedBy) side.
2.9.8. @CollectionType
The @CollectionType
annotation provides the ability to use a custom
UserCollectionType
implementation to influence how the collection for a plural attribute behaves.
As an example, consider a requirement for a collection with the semantics of a «unique list» — a
cross between the ordered-ness of a List
and the uniqueness of a Set
. First the entity:
Example 241. @CollectionType
@Entity
public class TheEntityWithUniqueList {
@ElementCollection
@CollectionType(type = UniqueListType.class)
private List<String> strings;
// ...
}
The mapping says to use the UniqueListType
class for the mapping of the plural attribute.
Example 242. UniqueListType
public class UniqueListType implements UserCollectionType {
@Override
public CollectionClassification getClassification() {
return CollectionClassification.LIST;
}
@Override
public Class<?> getCollectionClass() {
return List.class;
}
@Override
public PersistentCollection instantiate(
SharedSessionContractImplementor session,
CollectionPersister persister) {
return new UniqueListWrapper( session );
}
@Override
public PersistentCollection wrap(
SharedSessionContractImplementor session,
Object collection) {
return new UniqueListWrapper( session, (List) collection );
}
@Override
public Iterator getElementsIterator(Object collection) {
return ( (List) collection ).iterator();
}
@Override
public boolean contains(Object collection, Object entity) {
return ( (List) collection ).contains( entity );
}
@Override
public Object indexOf(Object collection, Object entity) {
return ( (List) collection ).indexOf( entity );
}
@Override
public Object replaceElements(
Object original,
Object target,
CollectionPersister persister,
Object owner,
Map copyCache,
SharedSessionContractImplementor session) {
List result = (List) target;
result.clear();
result.addAll( (List) original );
return result;
}
@Override
public Object instantiate(int anticipatedSize) {
return new ArrayList<>();
}
}
Most custom UserCollectionType
implementations will want their own PersistentCollection
implementation.
Example 243. UniqueListWrapper
public class UniqueListWrapper<E> extends PersistentList<E> {
public UniqueListWrapper(SharedSessionContractImplementor session) {
super( session );
}
public UniqueListWrapper(SharedSessionContractImplementor session, List<E> list) {
super( session, list );
}
// ...
}
UniqueListWrapper
is the PersistentCollection
implementation for the «unique list» semantic. See Wrappers for more details.
2.9.9. @CollectionTypeRegistration
For cases where an application wants to apply the same custom type to all
plural attributes of a given classification, Hibernate also provides the
@CollectionTypeRegistration
:
Example 244. UniqueListType Registration
@Entity
@CollectionTypeRegistration( type = UniqueListType.class, classification = CollectionClassification.LIST )
public class TheEntityWithUniqueListRegistration {
@ElementCollection
private List<String> strings;
// ...
}
This example behaves exactly as in @CollectionType.
2.9.10. Wrappers
As mentioned in Collection Semantics, Hibernate provides its own implementations
of the Java collection types. These are called wrappers as they wrap an underlying
collection and provide support for things like lazy loading, queueing add/remove
operations while detached, etc. Hibernate defines the following PersistentCollection
implementations for each of its collection classifications —
-
PersistentArrayHolder
-
PersistentBag
-
PersistentIdentifierBag
-
PersistentList
-
PersistentMap
-
PersistentSet
-
PersistentSortedMap
-
PersistentSortedSet
ORDERED_SET uses PersistentSet
for its wrapper and ORDERED_MAP uses PersistentMap
.
The collections they wrap are called «raw» collections, which are generally the standard
Java implementations (java.util.ArrayList
, etc)
2.9.11. Bags
Bags are unordered lists, and we can have unidirectional bags or bidirectional ones.
Unidirectional bags
The unidirectional bag is mapped using a single @OneToMany
annotation on the parent side of the association.
Behind the scenes, Hibernate requires an association table to manage the parent-child relationship, as we can see in the following example:
Example 245. Unidirectional bag
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(cascade = CascadeType.ALL)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
private String type;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Person_Phone (
Person_id BIGINT NOT NULL ,
phones_id BIGINT NOT NULL
)
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
type VARCHAR(255) ,
PRIMARY KEY ( id )
)
ALTER TABLE Person_Phone
ADD CONSTRAINT UK_9uhc5itwc9h5gcng944pcaslf
UNIQUE (phones_id)
ALTER TABLE Person_Phone
ADD CONSTRAINT FKr38us2n8g5p9rj0b494sd3391
FOREIGN KEY (phones_id) REFERENCES Phone
ALTER TABLE Person_Phone
ADD CONSTRAINT FK2ex4e4p7w1cj310kg2woisjl2
FOREIGN KEY (Person_id) REFERENCES Person
Because both the parent and the child sides are entities, the persistence context manages each entity separately. The cascading mechanism allows you to propagate an entity state transition from a parent entity to its children. |
By marking the parent side with the CascadeType.ALL
attribute, the unidirectional association lifecycle becomes very similar to that of a value type collection.
Example 246. Unidirectional bag lifecycle
Person person = new Person(1L);
person.getPhones().add(new Phone(1L, "landline", "028-234-9876"));
person.getPhones().add(new Phone(2L, "mobile", "072-122-9876"));
entityManager.persist(person);
INSERT INTO Person ( id )
VALUES ( 1 )
INSERT INTO Phone ( number, type, id )
VALUES ( '028-234-9876', 'landline', 1 )
INSERT INTO Phone ( number, type, id )
VALUES ( '072-122-9876', 'mobile', 2 )
INSERT INTO Person_Phone ( Person_id, phones_id )
VALUES ( 1, 1 )
INSERT INTO Person_Phone ( Person_id, phones_id )
VALUES ( 1, 2 )
In the example above, once the parent entity is persisted, the child entities are going to be persisted as well.
Just like value type collections, unidirectional bags are not as efficient when it comes to modifying the collection structure (removing or reshuffling elements). Because the parent-side cannot uniquely identify each individual child, Hibernate deletes all link table rows associated with the parent entity and re-adds the remaining ones that are found in the current collection state. |
Bidirectional bags
The bidirectional bag is the most common type of entity collection.
The @ManyToOne
side is the owning side of the bidirectional bag association, while the @OneToMany
is the inverse side, being marked with the mappedBy
attribute.
Example 247. Bidirectional bag
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
phones.add(phone);
phone.setPerson(this);
}
public void removePhone(Phone phone) {
phones.remove(phone);
phone.setPerson(null);
}
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
private String type;
@Column(name = "`number`", unique = true)
@NaturalId
private String number;
@ManyToOne
private Person person;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Phone phone = (Phone) o;
return Objects.equals(number, phone.number);
}
@Override
public int hashCode() {
return Objects.hash(number);
}
}
CREATE TABLE Person (
id BIGINT NOT NULL, PRIMARY KEY (id)
)
CREATE TABLE Phone (
id BIGINT NOT NULL,
number VARCHAR(255),
type VARCHAR(255),
person_id BIGINT,
PRIMARY KEY (id)
)
ALTER TABLE Phone
ADD CONSTRAINT UK_l329ab0g4c1t78onljnxmbnp6
UNIQUE (number)
ALTER TABLE Phone
ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg
FOREIGN KEy (person_id) REFERENCES Person
Example 248. Bidirectional bag lifecycle
person.addPhone(new Phone(1L, "landline", "028-234-9876"));
person.addPhone(new Phone(2L, "mobile", "072-122-9876"));
entityManager.flush();
person.removePhone(person.getPhones().get(0));
INSERT INTO Phone (number, person_id, type, id)
VALUES ( '028-234-9876', 1, 'landline', 1 )
INSERT INTO Phone (number, person_id, type, id)
VALUES ( '072-122-9876', 1, 'mobile', 2 )
UPDATE Phone
SET person_id = NULL, type = 'landline' where id = 1
Example 249. Bidirectional bag with orphan removal
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Phone> phones = new ArrayList<>();
DELETE FROM Phone WHERE id = 1
When rerunning the previous example, the child will get removed because the parent-side propagates the removal upon dissociating the child entity reference.
2.9.12. Ordered Lists
Although they use the List
interface on the Java side, bags don’t retain element order.
To preserve the collection element order, there are two possibilities:
@OrderBy
-
the collection is ordered upon retrieval using a child entity property
@OrderColumn
-
the collection uses a dedicated order column in the collection link table
Unidirectional ordered lists
When using the @OrderBy
annotation, the mapping looks as follows:
Example 250. Unidirectional @OrderBy
list
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(cascade = CascadeType.ALL)
@OrderBy("number")
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
private String type;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
The database mapping is the same as with the Unidirectional bags example, so it won’t be repeated.
Upon fetching the collection, Hibernate generates the following select statement:
Example 251. Unidirectional @OrderBy
list select statement
SELECT
phones0_.Person_id AS Person_i1_1_0_,
phones0_.phones_id AS phones_i2_1_0_,
unidirecti1_.id AS id1_2_1_,
unidirecti1_."number" AS number2_2_1_,
unidirecti1_.type AS type3_2_1_
FROM
Person_Phone phones0_
INNER JOIN
Phone unidirecti1_ ON phones0_.phones_id=unidirecti1_.id
WHERE
phones0_.Person_id = 1
ORDER BY
unidirecti1_."number"
The child table column is used to order the list elements.
The If no property is specified (e.g. |
Another ordering option is to use the @OrderColumn
annotation:
Example 252. Unidirectional @OrderColumn
list
@OneToMany(cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
private List<Phone> phones = new ArrayList<>();
CREATE TABLE Person_Phone (
Person_id BIGINT NOT NULL ,
phones_id BIGINT NOT NULL ,
order_id INTEGER NOT NULL ,
PRIMARY KEY ( Person_id, order_id )
)
This time, the link table takes the order_id
column and uses it to materialize the collection element order.
When fetching the list, the following select query is executed:
Example 253. Unidirectional @OrderColumn
list select statement
select
phones0_.Person_id as Person_i1_1_0_,
phones0_.phones_id as phones_i2_1_0_,
phones0_.order_id as order_id3_0_,
unidirecti1_.id as id1_2_1_,
unidirecti1_.number as number2_2_1_,
unidirecti1_.type as type3_2_1_
from
Person_Phone phones0_
inner join
Phone unidirecti1_
on phones0_.phones_id=unidirecti1_.id
where
phones0_.Person_id = 1
With the order_id
column in place, Hibernate can order the list in-memory after it’s being fetched from the database.
Bidirectional ordered lists
The mapping is similar with the Bidirectional bags example, just that the parent side is going to be annotated with either @OrderBy
or @OrderColumn
.
Example 254. Bidirectional @OrderBy
list
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderBy("number")
private List<Phone> phones = new ArrayList<>();
Just like with the unidirectional @OrderBy
list, the number
column is used to order the statement on the SQL level.
When using the @OrderColumn
annotation, the order_id
column is going to be embedded in the child table:
Example 255. Bidirectional @OrderColumn
list
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
private List<Phone> phones = new ArrayList<>();
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
type VARCHAR(255) ,
person_id BIGINT ,
order_id INTEGER ,
PRIMARY KEY ( id )
)
When fetching the collection, Hibernate will use the fetched ordered columns to sort the elements according to the @OrderColumn
mapping.
Customizing ordered list ordinal
You can customize the ordinal of the underlying ordered list by using the @ListIndexBase
annotation.
Example 256. @ListIndexBase
mapping example
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
@ListIndexBase(100)
private List<Phone> phones = new ArrayList<>();
When inserting two Phone
records, Hibernate is going to start the List index from 100 this time.
Example 257. @ListIndexBase
persist example
Person person = new Person(1L);
entityManager.persist(person);
person.addPhone(new Phone(1L, "landline", "028-234-9876"));
person.addPhone(new Phone(2L, "mobile", "072-122-9876"));
INSERT INTO Phone("number", person_id, type, id)
VALUES ('028-234-9876', 1, 'landline', 1)
INSERT INTO Phone("number", person_id, type, id)
VALUES ('072-122-9876', 1, 'mobile', 2)
UPDATE Phone
SET order_id = 100
WHERE id = 1
UPDATE Phone
SET order_id = 101
WHERE id = 2
Customizing ORDER BY SQL clause
While the Jakarta Persistence
@OrderBy
annotation allows you to specify the entity attributes used for sorting
when fetching the current annotated collection, the Hibernate specific
@OrderBy
annotation is used to specify a SQL clause instead.
In the following example, the @OrderBy
annotation uses the CHAR_LENGTH
SQL function to order the Article
entities
by the number of characters of the name
attribute.
Example 258. @OrderBy
mapping example
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
@OneToMany(
mappedBy = "person",
cascade = CascadeType.ALL
)
@SQLOrder("CHAR_LENGTH(name) DESC")
private List<Article> articles = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Article")
public static class Article {
@Id
@GeneratedValue
private Long id;
private String name;
private String content;
@ManyToOne(fetch = FetchType.LAZY)
private Person person;
//Getters and setters are omitted for brevity
}
When fetching the articles
collection, Hibernate uses the ORDER BY SQL clause provided by the mapping:
Example 259. @OrderBy
fetching example
Person person = entityManager.find(Person.class, 1L);
assertEquals(
"High-Performance Hibernate",
person.getArticles().get(0).getName()
);
select
a.person_id as person_i4_0_0_,
a.id as id1_0_0_,
a.content as content2_0_1_,
a.name as name3_0_1_,
a.person_id as person_i4_0_1_
from
Article a
where
a.person_id = ?
order by
CHAR_LENGTH(a.name) desc
2.9.13. Sets
Sets are collections that don’t allow duplicate entries and Hibernate supports both the unordered Set
and the natural-ordering SortedSet
.
Unidirectional sets
The unidirectional set uses a link table to hold the parent-child associations and the entity mapping looks as follows:
Example 260. Unidirectional set
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(cascade = CascadeType.ALL)
private Set<Phone> phones = new HashSet<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
private String type;
@NaturalId
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Phone phone = (Phone) o;
return Objects.equals(number, phone.number);
}
@Override
public int hashCode() {
return Objects.hash(number);
}
}
The unidirectional set lifecycle is similar to that of the Unidirectional bags, so it can be omitted.
The only difference is that Set
doesn’t allow duplicates, but this constraint is enforced by the Java object contract rather than the database mapping.
When using Sets, it’s very important to supply proper equals/hashCode implementations for child entities. In the absence of a custom equals/hashCode implementation logic, Hibernate will use the default Java reference-based object equality which might render unexpected results when mixing detached and managed object instances. |
Bidirectional sets
Just like bidirectional bags, the bidirectional set doesn’t use a link table, and the child table has a foreign key referencing the parent table primary key.
The lifecycle is just like with bidirectional bags except for the duplicates which are filtered out.
Example 261. Bidirectional set
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
private Set<Phone> phones = new HashSet<>();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
phones.add(phone);
phone.setPerson(this);
}
public void removePhone(Phone phone) {
phones.remove(phone);
phone.setPerson(null);
}
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
private String type;
@Column(name = "`number`", unique = true)
@NaturalId
private String number;
@ManyToOne
private Person person;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Phone phone = (Phone) o;
return Objects.equals(number, phone.number);
}
@Override
public int hashCode() {
return Objects.hash(number);
}
}
2.9.14. Sorted sets
For sorted sets, the entity mapping must use the SortedSet
interface instead.
According to the SortedSet
contract, all elements must implement the Comparable
interface and therefore provide the sorting logic.
Unidirectional sorted sets
A SortedSet
that relies on the natural sorting order given by the child element Comparable
implementation logic might be annotated with the @SortNatural
Hibernate annotation.
Example 262. Unidirectional natural sorted set
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(cascade = CascadeType.ALL)
@SortNatural
private SortedSet<Phone> phones = new TreeSet<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone implements Comparable<Phone> {
@Id
private Long id;
private String type;
@NaturalId
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
@Override
public int compareTo(Phone o) {
return number.compareTo(o.getNumber());
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Phone phone = (Phone) o;
return Objects.equals(number, phone.number);
}
@Override
public int hashCode() {
return Objects.hash(number);
}
}
The lifecycle and the database mapping are identical to the Unidirectional bags, so they are intentionally omitted.
To provide a custom sorting logic, Hibernate also provides a @SortComparator
annotation:
Example 263. Unidirectional custom comparator sorted set
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(cascade = CascadeType.ALL)
@SortComparator(ReverseComparator.class)
private SortedSet<Phone> phones = new TreeSet<>();
//Getters and setters are omitted for brevity
}
public static class ReverseComparator implements Comparator<Phone> {
@Override
public int compare(Phone o1, Phone o2) {
return o2.compareTo(o1);
}
}
@Entity(name = "Phone")
public static class Phone implements Comparable<Phone> {
@Id
private Long id;
private String type;
@NaturalId
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
@Override
public int compareTo(Phone o) {
return number.compareTo(o.getNumber());
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Phone phone = (Phone) o;
return Objects.equals(number, phone.number);
}
@Override
public int hashCode() {
return Objects.hash(number);
}
}
Bidirectional sorted sets
The @SortNatural
and @SortComparator
work the same for bidirectional sorted sets too:
Example 264. Bidirectional natural sorted set
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@SortNatural
private SortedSet<Phone> phones = new TreeSet<>();
//Getters and setters are omitted for brevity
Before v6, |
2.9.15. Maps
A java.util.Map
is a ternary association because it requires a parent entity, a map key, and a value.
An entity can either be a map key or a map value, depending on the mapping.
Hibernate allows using the following map keys:
MapKeyColumn
-
for value type maps, the map key is a column in the link table that defines the grouping logic
MapKey
-
the map key is either the primary key or another property of the entity stored as a map entry value
MapKeyEnumerated
-
the map key is an
Enum
of the target child entity MapKeyTemporal
-
the map key is a
Date
or aCalendar
of the target child entity MapKeyJoinColumn
-
the map key is an entity mapped as an association in the child entity that’s stored as a map entry key
Value type maps
A map of value type must use the @ElementCollection
annotation, just like value type lists, bags or sets.
Example 265. Value type map with an entity as a map key
public enum PhoneType {
LAND_LINE,
MOBILE
}
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@Temporal(TemporalType.TIMESTAMP)
@ElementCollection
@CollectionTable(name = "phone_register")
@Column(name = "since")
private Map<Phone, Date> phoneRegister = new HashMap<>();
//Getters and setters are omitted for brevity
}
@Embeddable
public static class Phone {
private PhoneType type;
@Column(name = "`number`")
private String number;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE phone_register (
Person_id BIGINT NOT NULL ,
since TIMESTAMP ,
number VARCHAR(255) NOT NULL ,
type INTEGER NOT NULL ,
PRIMARY KEY ( Person_id, number, type )
)
ALTER TABLE phone_register
ADD CONSTRAINT FKrmcsa34hr68of2rq8qf526mlk
FOREIGN KEY (Person_id) REFERENCES Person
Adding entries to the map generates the following SQL statements:
Example 266. Adding value type map entries
person.getPhoneRegister().put(
new Phone(PhoneType.LAND_LINE, "028-234-9876"), new Date()
);
person.getPhoneRegister().put(
new Phone(PhoneType.MOBILE, "072-122-9876"), new Date()
);
INSERT INTO phone_register (Person_id, number, type, since)
VALUES (1, '072-122-9876', 1, '2015-12-15 17:16:45.311')
INSERT INTO phone_register (Person_id, number, type, since)
VALUES (1, '028-234-9876', 0, '2015-12-15 17:16:45.311')
Maps with a custom key type
Hibernate defines the
@MapKeyType
annotation
which you can use to customize the Map
key type.
Considering you have the following tables in your database:
create table person (
id int8 not null,
primary key (id)
)
create table call_register (
person_id int8 not null,
phone_number int4,
call_timestamp_epoch int8 not null,
primary key (person_id, call_timestamp_epoch)
)
alter table if exists call_register
add constraint FKsn58spsregnjyn8xt61qkxsub
foreign key (person_id)
references person
The call_register
records the call history for every person
.
The call_timestamp_epoch
column stores the phone call timestamp as a Unix timestamp since the Unix epoch.
The |
Since we want to map all the calls by their associated java.util.Date
, not by their timestamp since epoch which is a number, the entity mapping looks as follows:
Example 267. @MapKeyType
mapping example
@Entity
@Table(name = "person")
public static class Person {
@Id
private Long id;
@ElementCollection
@CollectionTable(
name = "call_register",
joinColumns = @JoinColumn(name = "person_id")
)
@MapKeyJdbcTypeCode(Types.BIGINT)
@MapKeyJavaType(JdbcTimestampJavaType.class)
@MapKeyColumn(name = "call_timestamp_epoch")
@Column(name = "phone_number")
private Map<Date, Integer> callRegister = new HashMap<>();
//Getters and setters are omitted for brevity
}
Maps having an interface type as the key
Considering you have the following PhoneNumber
interface with an implementation given by the MobilePhone
class type:
Example 268. PhoneNumber
interface and the MobilePhone
class type
public interface PhoneNumber {
String get();
}
@Embeddable
public static class MobilePhone
implements PhoneNumber {
static PhoneNumber fromString(String phoneNumber) {
String[] tokens = phoneNumber.split("-");
if (tokens.length != 3) {
throw new IllegalArgumentException("invalid phone number: " + phoneNumber);
}
int i = 0;
return new MobilePhone(
tokens[i++],
tokens[i++],
tokens[i]
);
}
private MobilePhone() {
}
public MobilePhone(
String countryCode,
String operatorCode,
String subscriberCode) {
this.countryCode = countryCode;
this.operatorCode = operatorCode;
this.subscriberCode = subscriberCode;
}
@Column(name = "country_code")
private String countryCode;
@Column(name = "operator_code")
private String operatorCode;
@Column(name = "subscriber_code")
private String subscriberCode;
@Override
public String get() {
return String.format(
"%s-%s-%s",
countryCode,
operatorCode,
subscriberCode
);
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
MobilePhone that = (MobilePhone) o;
return Objects.equals(countryCode, that.countryCode) &&
Objects.equals(operatorCode, that.operatorCode) &&
Objects.equals(subscriberCode, that.subscriberCode);
}
@Override
public int hashCode() {
return Objects.hash(countryCode, operatorCode, subscriberCode);
}
}
If you want to use the PhoneNumber
interface as a java.util.Map
key, then you need to supply the
@MapKeyClass
annotation as well.
Example 269. @MapKeyClass
mapping example
@Entity
@Table(name = "person")
public static class Person {
@Id
private Long id;
@ElementCollection
@CollectionTable(
name = "call_register",
joinColumns = @JoinColumn(name = "person_id")
)
@MapKeyColumn(name = "call_timestamp_epoch")
@MapKeyClass(MobilePhone.class)
@Column(name = "call_register")
private Map<PhoneNumber, Integer> callRegister = new HashMap<>();
//Getters and setters are omitted for brevity
}
create table person (
id bigint not null,
primary key (id)
)
create table call_register (
person_id bigint not null,
call_register integer,
country_code varchar(255) not null,
operator_code varchar(255) not null,
subscriber_code varchar(255) not null,
primary key (person_id, country_code, operator_code, subscriber_code)
)
alter table call_register
add constraint FKqyj2at6ik010jqckeaw23jtv2
foreign key (person_id)
references person
When inserting a Person
with a callRegister
containing 2 MobilePhone
references,
Hibernate generates the following SQL statements:
Example 270. @MapKeyClass
persist example
Person person = new Person();
person.setId(1L);
person.getCallRegister().put(new MobilePhone("01", "234", "567"), 101);
person.getCallRegister().put(new MobilePhone("01", "234", "789"), 102);
entityManager.persist(person);
insert into person (id) values (?)
-- binding parameter [1] as [BIGINT] - [1]
insert into call_register(
person_id,
country_code,
operator_code,
subscriber_code,
call_register
)
values
(?, ?, ?, ?, ?)
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [VARCHAR] - [01]
-- binding parameter [3] as [VARCHAR] - [234]
-- binding parameter [4] as [VARCHAR] - [789]
-- binding parameter [5] as [INTEGER] - [102]
insert into call_register(
person_id,
country_code,
operator_code,
subscriber_code,
call_register
)
values
(?, ?, ?, ?, ?)
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [VARCHAR] - [01]
-- binding parameter [3] as [VARCHAR] - [234]
-- binding parameter [4] as [VARCHAR] - [567]
-- binding parameter [5] as [INTEGER] - [101]
When fetching a Person
and accessing the callRegister
Map
,
Hibernate generates the following SQL statements:
Example 271. @MapKeyClass
fetch example
Person person = entityManager.find(Person.class, 1L);
assertEquals(2, person.getCallRegister().size());
assertEquals(
Integer.valueOf(101),
person.getCallRegister().get(MobilePhone.fromString("01-234-567"))
);
assertEquals(
Integer.valueOf(102),
person.getCallRegister().get(MobilePhone.fromString("01-234-789"))
);
select
cr.person_id as person_i1_0_0_,
cr.call_register as call_reg2_0_0_,
cr.country_code as country_3_0_,
cr.operator_code as operator4_0_,
cr.subscriber_code as subscrib5_0_
from
call_register cr
where
cr.person_id = ?
-- binding parameter [1] as [BIGINT] - [1]
-- extracted value ([person_i1_0_0_] : [BIGINT]) - [1]
-- extracted value ([call_reg2_0_0_] : [INTEGER]) - [101]
-- extracted value ([country_3_0_] : [VARCHAR]) - [01]
-- extracted value ([operator4_0_] : [VARCHAR]) - [234]
-- extracted value ([subscrib5_0_] : [VARCHAR]) - [567]
-- extracted value ([person_i1_0_0_] : [BIGINT]) - [1]
-- extracted value ([call_reg2_0_0_] : [INTEGER]) - [102]
-- extracted value ([country_3_0_] : [VARCHAR]) - [01]
-- extracted value ([operator4_0_] : [VARCHAR]) - [234]
-- extracted value ([subscrib5_0_] : [VARCHAR]) - [789]
Unidirectional maps
A unidirectional map exposes a parent-child association from the parent-side only.
The following example shows a unidirectional map which also uses a @MapKeyTemporal
annotation.
The map key is a timestamp, and it’s taken from the child entity table.
The |
Example 272. Unidirectional Map
public enum PhoneType {
LAND_LINE,
MOBILE
}
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
@JoinTable(
name = "phone_register",
joinColumns = @JoinColumn(name = "phone_id"),
inverseJoinColumns = @JoinColumn(name = "person_id"))
@MapKey(name = "since")
@MapKeyTemporal(TemporalType.TIMESTAMP)
private Map<Date, Phone> phoneRegister = new HashMap<>();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
phoneRegister.put(phone.getSince(), phone);
}
}
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
private PhoneType type;
@Column(name = "`number`")
private String number;
private Date since;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
since TIMESTAMP ,
type INTEGER ,
PRIMARY KEY ( id )
)
CREATE TABLE phone_register (
phone_id BIGINT NOT NULL ,
person_id BIGINT NOT NULL ,
PRIMARY KEY ( phone_id, person_id )
)
ALTER TABLE phone_register
ADD CONSTRAINT FKc3jajlx41lw6clbygbw8wm65w
FOREIGN KEY (person_id) REFERENCES Phone
ALTER TABLE phone_register
ADD CONSTRAINT FK6npoomh1rp660o1b55py9ndw4
FOREIGN KEY (phone_id) REFERENCES Person
Bidirectional maps
Like most bidirectional associations, this relationship is owned by the child-side while the parent is the inverse side and can propagate its own state transitions to the child entities.
In the following example, you can see that @MapKeyEnumerated
was used so that the Phone
enumeration becomes the map key.
Example 273. Bidirectional Map
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
@MapKey(name = "type")
@MapKeyEnumerated
private Map<PhoneType, Phone> phoneRegister = new HashMap<>();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
phone.setPerson(this);
phoneRegister.put(phone.getType(), phone);
}
}
@Entity(name = "Phone")
public static class Phone {
@Id
@GeneratedValue
private Long id;
private PhoneType type;
@Column(name = "`number`")
private String number;
private Date since;
@ManyToOne
private Person person;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE Phone (
id BIGINT NOT NULL ,
number VARCHAR(255) ,
since TIMESTAMP ,
type INTEGER ,
person_id BIGINT ,
PRIMARY KEY ( id )
)
ALTER TABLE Phone
ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg
FOREIGN KEY (person_id) REFERENCES Person
2.9.16. Arrays
When discussing arrays, it is important to understand the distinction between SQL array types and Java arrays that are mapped as part of the application’s domain model.
Not all databases implement the SQL-99 ARRAY type and, for this reason,
the SQL type used by Hibernate for arrays varies depending on the database support.
It is impossible for Hibernate to offer lazy-loading for arrays of entities and, for this reason, it is strongly recommended to map a «collection» of entities using a List or Set rather than an array. |
2.9.17. Arrays as basic value type
By default, Hibernate will choose a type for the array based on Dialect.getPreferredSqlTypeCodeForArray()
.
Prior to Hibernate 6.1, the default was to always use the BINARY type, as supported by the current Dialect
,
but now, Hibernate will leverage the native array data types if possible.
To force the BINARY type, the persistent attribute has to be annotated with @JdbcTypeCode(SqlTypes.VARBINARY)
.
Example 274. Arrays stored as SQL array
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String[] phones;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL,
phones VARCHAR(255) ARRAY,
PRIMARY KEY ( id )
)
2.9.18. Collections as basic value type
Notice how all the previous examples explicitly mark the collection attribute as either @ElementCollection
,
@OneToMany
or @ManyToMany
.
Attributes of collection or array type without any of those annotations are considered basic types and by
default mapped like basic arrays as depicted in the previous section.
Example 275. Collections stored as SQL array
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private List<String> phones;
//Getters and setters are omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL,
phones VARCHAR(255) ARRAY,
PRIMARY KEY ( id )
)
Prior to Hibernate 6.1, it was common to use an AttributeConverter to map the elements
into e.g. a comma separated list which is still a viable option. Just note that it is not required anymore.
Example 276. Comma delimited collection
public class CommaDelimitedStringsConverter implements AttributeConverter<List<String>,String> {
@Override
public String convertToDatabaseColumn(List<String> attributeValue) {
if ( attributeValue == null ) {
return null;
}
return join( ",", attributeValue );
}
@Override
public List<String> convertToEntityAttribute(String dbData) {
if ( dbData == null ) {
return null;
}
return listOf( dbData.split( "," ) );
}
}
@Entity( name = "Person" )
public static class Person {
@Id
private Integer id;
@Basic
private String name;
@Basic
@Convert( converter = CommaDelimitedStringsConverter.class )
private List<String> nickNames;
// ...
}
2.10. Natural Ids
Natural ids represent domain model unique identifiers that have a meaning in the real world too.
Even if a natural id does not make a good primary key (surrogate keys being usually preferred), it’s still useful to tell Hibernate about it.
As we will see later, Hibernate provides a dedicated, efficient API for loading an entity by its natural id much like it offers for loading by its identifier (PK).
2.10.1. Natural Id Mapping
Natural ids are defined in terms of one or more persistent attributes.
Example 277. Natural id using single basic attribute
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
@NaturalId
private String isbn;
//Getters and setters are omitted for brevity
}
Example 278. Natural id using single embedded attribute
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
@NaturalId
@Embedded
private Isbn isbn;
//Getters and setters are omitted for brevity
}
@Embeddable
public static class Isbn implements Serializable {
private String isbn10;
private String isbn13;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Isbn isbn = (Isbn) o;
return Objects.equals(isbn10, isbn.isbn10) &&
Objects.equals(isbn13, isbn.isbn13);
}
@Override
public int hashCode() {
return Objects.hash(isbn10, isbn13);
}
}
Example 279. Natural id using multiple persistent attributes
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
@NaturalId
private String productNumber;
@NaturalId
@ManyToOne(fetch = FetchType.LAZY)
private Publisher publisher;
//Getters and setters are omitted for brevity
}
@Entity(name = "Publisher")
public static class Publisher implements Serializable {
@Id
private Long id;
private String name;
//Getters and setters are omitted for brevity
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Publisher publisher = (Publisher) o;
return Objects.equals(id, publisher.id) &&
Objects.equals(name, publisher.name);
}
@Override
public int hashCode() {
return Objects.hash(id, name);
}
}
2.10.2. Natural Id API
As stated before, Hibernate provides an API for loading entities by their associated natural id.
This is represented by the org.hibernate.NaturalIdLoadAccess
contract obtained via Session#byNaturalId.
If the entity does not define a natural id, trying to load an entity by its natural id will throw an exception. |
Example 280. Using NaturalIdLoadAccess
Book book = entityManager
.unwrap(Session.class)
.byNaturalId(Book.class)
.using("isbn", "978-9730228236")
.load();
Book book = entityManager
.unwrap(Session.class)
.byNaturalId(Book.class)
.using(
"isbn",
new Isbn(
"973022823X",
"978-9730228236"
))
.load();
Book book = entityManager
.unwrap(Session.class)
.byNaturalId(Book.class)
.using("productNumber", "973022823X")
.using("publisher", publisher)
.load();
NaturalIdLoadAccess offers 2 distinct methods for obtaining the entity:
load()
-
obtains a reference to the entity, making sure that the entity state is initialized.
getReference()
-
obtains a reference to the entity. The state may or may not be initialized.
If the entity is already associated with the current running Session, that reference (loaded or not) is returned.
If the entity is not loaded in the current Session and the entity supports proxy generation, an uninitialized proxy is generated and returned, otherwise the entity is loaded from the database and returned.
NaturalIdLoadAccess
allows loading an entity by natural id and at the same time applies a pessimistic lock.
For additional details on locking, see the Locking chapter.
We will discuss the last method available on NaturalIdLoadAccess ( setSynchronizationEnabled()
) in Natural Id — Mutability and Caching.
Because the Book
entities in the first two examples define «simple» natural ids, we can load them as follows:
Example 281. Loading by simple natural id
Book book = entityManager
.unwrap(Session.class)
.bySimpleNaturalId(Book.class)
.load("978-9730228236");
Book book = entityManager
.unwrap(Session.class)
.bySimpleNaturalId(Book.class)
.load(
new Isbn(
"973022823X",
"978-9730228236"
)
);
Here we see the use of the org.hibernate.SimpleNaturalIdLoadAccess
contract,
obtained via Session#bySimpleNaturalId()
.
SimpleNaturalIdLoadAccess
is similar to NaturalIdLoadAccess
except that it does not define the using method.
Instead, because these simple natural ids are defined based on just one attribute we can directly pass
the corresponding natural id attribute value directly to the load()
and getReference()
methods.
If the entity does not define a natural id, or if the natural id is not of a «simple» type, an exception will be thrown there. |
2.10.3. Natural Id — Mutability and Caching
A natural id may be mutable or immutable. By default the @NaturalId
annotation marks an immutable natural id attribute.
An immutable natural id is expected to never change its value.
If the value(s) of the natural id attribute(s) change, @NaturalId(mutable = true)
should be used instead.
Example 282. Mutable natural id mapping
@Entity(name = "Author")
public static class Author {
@Id
private Long id;
private String name;
@NaturalId(mutable = true)
private String email;
//Getters and setters are omitted for brevity
}
Within the Session, Hibernate maintains a mapping from natural id values to entity identifiers (PK) values.
If natural ids values changed, it is possible for this mapping to become out of date until a flush occurs.
To work around this condition, Hibernate will attempt to discover any such pending changes and adjust them when the load()
or getReference()
methods are executed.
To be clear: this is only pertinent for mutable natural ids.
This discovery and adjustment have a performance impact. |
Example 283. Mutable natural id synchronization use-case
Author author = entityManager
.unwrap(Session.class)
.bySimpleNaturalId(Author.class)
.load("john@acme.com");
author.setEmail("john.doe@acme.com");
assertNull(
entityManager
.unwrap(Session.class)
.bySimpleNaturalId(Author.class)
.setSynchronizationEnabled(false)
.load("john.doe@acme.com")
);
assertSame(author,
entityManager
.unwrap(Session.class)
.bySimpleNaturalId(Author.class)
.setSynchronizationEnabled(true)
.load("john.doe@acme.com")
);
Not only can this NaturalId-to-PK resolution be cached in the Session, but we can also have it cached in the second-level cache if second level caching is enabled.
Example 284. Natural id caching
@Entity(name = "Book")
@NaturalIdCache
public static class Book {
@Id
private Long id;
private String title;
private String author;
@NaturalId
private String isbn;
//Getters and setters are omitted for brevity
}
2.11. Partitioning
In data management, it is sometimes necessary to split data of a table into various (physical) partitions,
based on partition keys and a partitioning scheme.
Due to the nature of partitioning, it is vital for the database to know the partition key of a row for certain operations,
like SQL update and delete statements. If a database doesn’t know the partition of a row that should be updated or deleted,
then it must look for the row in all partitions, leading to poor performance.
The @PartitionKey
annotation is a way to tell Hibernate about the column, such that it can include a column restriction as
predicate into SQL update and delete statements for entity state changes.
2.11.1. Partition Key Mapping
Partition keys are defined in terms of one or more persistent attributes.
Example 285. Partition key using single basic attribute
@Entity(name = "User")
public static class User {
@Id
private Long id;
private String firstname;
private String lastname;
@PartitionKey
private String tenantKey;
//Getters and setters are omitted for brevity
}
When updating or deleting an entity, Hibernate will include a partition key constraint similar to this
update user_tbl set firstname=?,lastname=?,tenantKey=? where id=? and tenantKey=?
delete from user_tbl where id=? and tenantKey=?
2.12. Dynamic Model
Jakarta Persistence only acknowledges the POJO entity model mapping so, if you are concerned about Jakarta Persistence provider portability, it’s best to stick to the strict POJO model. |
2.12.1. Dynamic mapping models
Persistent entities do not necessarily have to be represented as POJO/JavaBean classes.
Hibernate also supports dynamic models (using Map
of Map
s at runtime).
With this approach, you do not write persistent classes, only mapping files.
A given entity has just one entity mode within a given SessionFactory.
This is a change from previous versions which allowed to define multiple entity modes for an entity and to select which to load.
Entity modes can now be mixed within a domain model; a dynamic entity might reference a POJO entity and vice versa.
Example 286. Dynamic domain model Hibernate mapping
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class entity-name="Book">
<id name="isbn" column="isbn" length="32" type="string"/>
<property name="title" not-null="true" length="50" type="string"/>
<property name="author" not-null="true" length="50" type="string"/>
</class>
</hibernate-mapping>
After you defined your entity mapping, you need to instruct Hibernate to use the dynamic mapping mode:
Example 287. Dynamic domain model Hibernate mapping
settings.put("hibernate.default_entity_mode", "dynamic-map");
When you are going to save the following Book
dynamic entity,
Hibernate is going to generate the following SQL statement:
Example 288. Persist dynamic entity
Map<String, String> book = new HashMap<>();
book.put("isbn", "978-9730228236");
book.put("title", "High-Performance Java Persistence");
book.put("author", "Vlad Mihalcea");
entityManager
.unwrap(Session.class)
.persist("Book", book);
insert
into
Book
(title, author, isbn)
values
(?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [2] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [3] as [VARCHAR] - [978-9730228236]
The main advantage of dynamic models is the quick turnaround time for prototyping without the need for entity class implementation. It is also interesting to note that dynamic models are great for certain integration use cases as well. |
2.13. Inheritance
Although relational database systems don’t provide support for inheritance, Hibernate provides several strategies to leverage this object-oriented trait onto domain model entities:
- MappedSuperclass
-
Inheritance is implemented in the domain model only without reflecting it in the database schema. See MappedSuperclass.
- Single table
-
The domain model class hierarchy is materialized into a single table which contains entities belonging to different class types. See Single table.
- Joined table
-
The base class and all the subclasses have their own database tables and fetching a subclass entity requires a join with the parent table as well. See Joined table.
- Table per class
-
Each subclass has its own table containing both the subclass and the base class properties. See Table per class.
2.13.1. MappedSuperclass
In the following domain model class hierarchy, a DebitAccount
and a CreditAccount
share the same Account
base class.
When using MappedSuperclass
, the inheritance is visible in the domain model only, and each database table contains both the base class and the subclass properties.
Example 289. @MappedSuperclass
inheritance
@MappedSuperclass
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
CREATE TABLE DebitAccount (
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
overdraftFee NUMERIC(19, 2) ,
PRIMARY KEY ( id )
)
CREATE TABLE CreditAccount (
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
creditLimit NUMERIC(19, 2) ,
PRIMARY KEY ( id )
)
Because the |
2.13.2. Single table
The single table inheritance strategy maps all subclasses to only one database table.
Each subclass declares its own persistent properties.
Version and id properties are assumed to be inherited from the root class.
When omitting an explicit inheritance strategy (e.g. |
Example 290. Single Table inheritance
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
CREATE TABLE Account (
DTYPE VARCHAR(31) NOT NULL ,
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
overdraftFee NUMERIC(19, 2) ,
creditLimit NUMERIC(19, 2) ,
PRIMARY KEY ( id )
)
Each subclass in a hierarchy must define a unique discriminator value, which is used to differentiate between rows belonging to separate subclass types.
If this is not specified, the DTYPE
column is used as a discriminator, storing the associated subclass name.
Example 291. Single Table inheritance discriminator column
DebitAccount debitAccount = new DebitAccount();
debitAccount.setId(1L);
debitAccount.setOwner("John Doe");
debitAccount.setBalance(BigDecimal.valueOf(100));
debitAccount.setInterestRate(BigDecimal.valueOf(1.5d));
debitAccount.setOverdraftFee(BigDecimal.valueOf(25));
CreditAccount creditAccount = new CreditAccount();
creditAccount.setId(2L);
creditAccount.setOwner("John Doe");
creditAccount.setBalance(BigDecimal.valueOf(1000));
creditAccount.setInterestRate(BigDecimal.valueOf(1.9d));
creditAccount.setCreditLimit(BigDecimal.valueOf(5000));
entityManager.persist(debitAccount);
entityManager.persist(creditAccount);
INSERT INTO Account (balance, interestRate, owner, overdraftFee, DTYPE, id)
VALUES (100, 1.5, 'John Doe', 25, 'DebitAccount', 1)
INSERT INTO Account (balance, interestRate, owner, creditLimit, DTYPE, id)
VALUES (1000, 1.9, 'John Doe', 5000, 'CreditAccount', 2)
When using polymorphic queries, only a single table is required to be scanned to fetch all associated subclass instances.
Example 292. Single Table polymorphic query
List<Account> accounts = entityManager
.createQuery("select a from Account a")
.getResultList();
SELECT singletabl0_.id AS id2_0_ ,
singletabl0_.balance AS balance3_0_ ,
singletabl0_.interestRate AS interest4_0_ ,
singletabl0_.owner AS owner5_0_ ,
singletabl0_.overdraftFee AS overdraf6_0_ ,
singletabl0_.creditLimit AS creditLi7_0_ ,
singletabl0_.DTYPE AS DTYPE1_0_
FROM Account singletabl0_
Among all other inheritance alternatives, the single table strategy performs the best since it requires access to one table only. |
Discriminator
The discriminator column contains marker values that tell the persistence layer what subclass to instantiate for a particular row.
Hibernate Core supports the following restricted set of types as discriminator column: String
, char
, int
, byte
, short
, boolean
(including yes_no
, true_false
).
Use the @DiscriminatorColumn
to define the discriminator column as well as the discriminator type.
The enum
The The second option, |
There used to be a |
Discriminator formula
Assuming a legacy database schema where the discriminator is based on inspecting a certain column,
we can take advantage of the Hibernate specific @DiscriminatorFormula
annotation and map the inheritance model as follows:
Example 293. Single Table discriminator formula
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorFormula(
"case when debitKey is not null " +
"then 'Debit' " +
"else (" +
" case when creditKey is not null " +
" then 'Credit' " +
" else 'Unknown' " +
" end) " +
"end "
)
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
@DiscriminatorValue(value = "Debit")
public static class DebitAccount extends Account {
private String debitKey;
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
@DiscriminatorValue(value = "Credit")
public static class CreditAccount extends Account {
private String creditKey;
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
CREATE TABLE Account (
id int8 NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
debitKey VARCHAR(255) ,
overdraftFee NUMERIC(19, 2) ,
creditKey VARCHAR(255) ,
creditLimit NUMERIC(19, 2) ,
PRIMARY KEY ( id )
)
The @DiscriminatorFormula
defines a custom SQL clause that can be used to identify a certain subclass type.
The @DiscriminatorValue
defines the mapping between the result of the @DiscriminatorFormula
and the inheritance subclass type.
Implicit discriminator values
Aside from the usual discriminator values assigned to each individual subclass type, the @DiscriminatorValue
can take two additional values:
null
-
If the underlying discriminator column is null, the
null
discriminator mapping is going to be used. not null
-
If the underlying discriminator column has a not-null value that is not explicitly mapped to any entity, the
not-null
discriminator mapping used.
To understand how these two values work, consider the following entity mapping:
Example 294. @DiscriminatorValue null
and not-null
entity mapping
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorValue("null")
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
@DiscriminatorValue("Debit")
public static class DebitAccount extends Account {
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
@DiscriminatorValue("Credit")
public static class CreditAccount extends Account {
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
@Entity(name = "OtherAccount")
@DiscriminatorValue("not null")
public static class OtherAccount extends Account {
private boolean active;
//Getters and setters are omitted for brevity
}
The Account
class has a @DiscriminatorValue( "null" )
mapping, meaning that any account
row which does not contain any discriminator value will be mapped to an Account
base class entity.
The DebitAccount
and CreditAccount
entities use explicit discriminator values.
The OtherAccount
entity is used as a generic account type because it maps any database row whose discriminator column is not explicitly assigned to any other entity in the current inheritance tree.
To visualize how it works, consider the following example:
Example 295. @DiscriminatorValue null
and not-null
entity persistence
DebitAccount debitAccount = new DebitAccount();
debitAccount.setId(1L);
debitAccount.setOwner("John Doe");
debitAccount.setBalance(BigDecimal.valueOf(100));
debitAccount.setInterestRate(BigDecimal.valueOf(1.5d));
debitAccount.setOverdraftFee(BigDecimal.valueOf(25));
CreditAccount creditAccount = new CreditAccount();
creditAccount.setId(2L);
creditAccount.setOwner("John Doe");
creditAccount.setBalance(BigDecimal.valueOf(1000));
creditAccount.setInterestRate(BigDecimal.valueOf(1.9d));
creditAccount.setCreditLimit(BigDecimal.valueOf(5000));
Account account = new Account();
account.setId(3L);
account.setOwner("John Doe");
account.setBalance(BigDecimal.valueOf(1000));
account.setInterestRate(BigDecimal.valueOf(1.9d));
entityManager.persist(debitAccount);
entityManager.persist(creditAccount);
entityManager.persist(account);
entityManager.unwrap(Session.class).doWork(connection -> {
try(Statement statement = connection.createStatement()) {
statement.executeUpdate(
"insert into Account (DTYPE, active, balance, interestRate, owner, id) " +
"values ('Other', true, 25, 0.5, 'Vlad', 4)"
);
}
});
Map<Long, Account> accounts = entityManager.createQuery(
"select a from Account a", Account.class)
.getResultList()
.stream()
.collect(Collectors.toMap(Account::getId, Function.identity()));
assertEquals(4, accounts.size());
assertEquals(DebitAccount.class, accounts.get(1L).getClass());
assertEquals(CreditAccount.class, accounts.get(2L).getClass());
assertEquals(Account.class, accounts.get(3L).getClass());
assertEquals(OtherAccount.class, accounts.get(4L).getClass());
INSERT INTO Account (balance, interestRate, owner, overdraftFee, DTYPE, id)
VALUES (100, 1.5, 'John Doe', 25, 'Debit', 1)
INSERT INTO Account (balance, interestRate, owner, overdraftFee, DTYPE, id)
VALUES (1000, 1.9, 'John Doe', 5000, 'Credit', 2)
INSERT INTO Account (balance, interestRate, owner, id)
VALUES (1000, 1.9, 'John Doe', 3)
INSERT INTO Account (DTYPE, active, balance, interestRate, owner, id)
VALUES ('Other', true, 25, 0.5, 'Vlad', 4)
SELECT a.id as id2_0_,
a.balance as balance3_0_,
a.interestRate as interest4_0_,
a.owner as owner5_0_,
a.overdraftFee as overdraf6_0_,
a.creditLimit as creditLi7_0_,
a.active as active8_0_,
a.DTYPE as DTYPE1_0_
FROM Account a
As you can see, the Account
entity row has a value of NULL
in the DTYPE
discriminator column,
while the OtherAccount
entity was saved with a DTYPE
column value of other
which has not explicit mapping.
2.13.3. Joined table
Each subclass can also be mapped to its own table.
This is also called table-per-subclass mapping strategy.
An inherited state is retrieved by joining with the table of the superclass.
A discriminator column is not required for this mapping strategy.
Each subclass must, however, declare a table column holding the object identifier.
Example 296. Join Table
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.JOINED)
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
CREATE TABLE Account (
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE CreditAccount (
creditLimit NUMERIC(19, 2) ,
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
CREATE TABLE DebitAccount (
overdraftFee NUMERIC(19, 2) ,
id BIGINT NOT NULL ,
PRIMARY KEY ( id )
)
ALTER TABLE CreditAccount
ADD CONSTRAINT FKihw8h3j1k0w31cnyu7jcl7n7n
FOREIGN KEY (id) REFERENCES Account
ALTER TABLE DebitAccount
ADD CONSTRAINT FKia914478noepymc468kiaivqm
FOREIGN KEY (id) REFERENCES Account
The primary keys of the The table name still defaults to the non-qualified class name. |
Example 297. Join Table with @PrimaryKeyJoinColumn
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.JOINED)
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
@PrimaryKeyJoinColumn(name = "account_id")
public static class DebitAccount extends Account {
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
@PrimaryKeyJoinColumn(name = "account_id")
public static class CreditAccount extends Account {
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
CREATE TABLE CreditAccount (
creditLimit NUMERIC(19, 2) ,
account_id BIGINT NOT NULL ,
PRIMARY KEY ( account_id )
)
CREATE TABLE DebitAccount (
overdraftFee NUMERIC(19, 2) ,
account_id BIGINT NOT NULL ,
PRIMARY KEY ( account_id )
)
ALTER TABLE CreditAccount
ADD CONSTRAINT FK8ulmk1wgs5x7igo370jt0q005
FOREIGN KEY (account_id) REFERENCES Account
ALTER TABLE DebitAccount
ADD CONSTRAINT FK7wjufa570onoidv4omkkru06j
FOREIGN KEY (account_id) REFERENCES Account
When using polymorphic queries, the base class table must be joined with all subclass tables to fetch every associated subclass instance.
Example 298. Join Table polymorphic query
List<Account> accounts = entityManager
.createQuery("select a from Account a")
.getResultList();
SELECT jointablet0_.id AS id1_0_ ,
jointablet0_.balance AS balance2_0_ ,
jointablet0_.interestRate AS interest3_0_ ,
jointablet0_.owner AS owner4_0_ ,
jointablet0_1_.overdraftFee AS overdraf1_2_ ,
jointablet0_2_.creditLimit AS creditLi1_1_ ,
CASE WHEN jointablet0_1_.id IS NOT NULL THEN 1
WHEN jointablet0_2_.id IS NOT NULL THEN 2
WHEN jointablet0_.id IS NOT NULL THEN 0
END AS clazz_
FROM Account jointablet0_
LEFT OUTER JOIN DebitAccount jointablet0_1_ ON jointablet0_.id = jointablet0_1_.id
LEFT OUTER JOIN CreditAccount jointablet0_2_ ON jointablet0_.id = jointablet0_2_.id
The joined table inheritance polymorphic queries can use several JOINS which might affect performance when fetching a large number of entities. |
2.13.4. Table per class
A third option is to map only the concrete classes of an inheritance hierarchy to tables.
This is called the table-per-concrete-class strategy.
Each table defines all persistent states of the class, including the inherited state.
In Hibernate, it is not necessary to explicitly map such inheritance hierarchies.
You can map each class as a separate entity root.
However, if you wish to use polymorphic associations (e.g. an association to the superclass of your hierarchy), you need to use the union subclass mapping.
Example 299. Table per class
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public static class Account {
@Id
private Long id;
private String owner;
private BigDecimal balance;
private BigDecimal interestRate;
//Getters and setters are omitted for brevity
}
@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {
private BigDecimal overdraftFee;
//Getters and setters are omitted for brevity
}
@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {
private BigDecimal creditLimit;
//Getters and setters are omitted for brevity
}
CREATE TABLE Account (
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
PRIMARY KEY ( id )
)
CREATE TABLE CreditAccount (
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
creditLimit NUMERIC(19, 2) ,
PRIMARY KEY ( id )
)
CREATE TABLE DebitAccount (
id BIGINT NOT NULL ,
balance NUMERIC(19, 2) ,
interestRate NUMERIC(19, 2) ,
owner VARCHAR(255) ,
overdraftFee NUMERIC(19, 2) ,
PRIMARY KEY ( id )
)
When using polymorphic queries, a UNION is required to fetch the base class table along with all subclass tables as well.
Example 300. Table per class polymorphic query
List<Account> accounts = entityManager
.createQuery("select a from Account a")
.getResultList();
SELECT tablepercl0_.id AS id1_0_ ,
tablepercl0_.balance AS balance2_0_ ,
tablepercl0_.interestRate AS interest3_0_ ,
tablepercl0_.owner AS owner4_0_ ,
tablepercl0_.overdraftFee AS overdraf1_2_ ,
tablepercl0_.creditLimit AS creditLi1_1_ ,
tablepercl0_.clazz_ AS clazz_
FROM (
SELECT id ,
balance ,
interestRate ,
owner ,
CAST(NULL AS INT) AS overdraftFee ,
CAST(NULL AS INT) AS creditLimit ,
0 AS clazz_
FROM Account
UNION ALL
SELECT id ,
balance ,
interestRate ,
owner ,
overdraftFee ,
CAST(NULL AS INT) AS creditLimit ,
1 AS clazz_
FROM DebitAccount
UNION ALL
SELECT id ,
balance ,
interestRate ,
owner ,
CAST(NULL AS INT) AS overdraftFee ,
creditLimit ,
2 AS clazz_
FROM CreditAccount
) tablepercl0_
Polymorphic queries require multiple UNION queries, so be aware of the performance implications of a large class hierarchy. |
2.13.5. Implicit and explicit polymorphism
By default, when you query a base class entity,
the polymorphic query will fetch all subclasses belonging to the base type.
However, you can even query
interfaces or base classes that don’t belong to the Jakarta Persistence entity inheritance model.
For instance, considering the following DomainModelEntity
interface:
Example 301. DomainModelEntity interface
public interface DomainModelEntity<ID> {
ID getId();
Integer getVersion();
}
If we have two entity mappings, a Book
and a Blog
,
and the Blog
entity is mapped with the
@Polymorphism
annotation
and taking the PolymorphismType.EXPLICIT
setting:
Example 302. @Polymorphism
entity mapping
@Entity(name = "Event")
public static class Book implements DomainModelEntity<Long> {
@Id
private Long id;
@Version
private Integer version;
private String title;
private String author;
//Getter and setters omitted for brevity
}
@Entity(name = "Blog")
@Polymorphism(type = PolymorphismType.EXPLICIT)
public static class Blog implements DomainModelEntity<Long> {
@Id
private Long id;
@Version
private Integer version;
private String site;
//Getter and setters omitted for brevity
}
If we have the following entity objects in our system:
Example 303. Domain Model entity objects
Book book = new Book();
book.setId(1L);
book.setAuthor("Vlad Mihalcea");
book.setTitle("High-Performance Java Persistence");
entityManager.persist(book);
Blog blog = new Blog();
blog.setId(1L);
blog.setSite("vladmihalcea.com");
entityManager.persist(blog);
We can now query against the DomainModelEntity
interface,
and Hibernate is going to fetch only the entities that are either mapped with
@Polymorphism(type = PolymorphismType.IMPLICIT)
or they are not annotated at all with the @Polymorphism
annotation (implying the IMPLICIT behavior):
Example 304. Fetching Domain Model entities using non-mapped base class polymorphism
List<DomainModelEntity> accounts = entityManager
.createQuery(
"select e " +
"from org.hibernate.orm.test.inheritance.polymorphism.DomainModelEntity e")
.getResultList();
assertEquals(1, accounts.size());
assertTrue(accounts.get(0) instanceof Book);
Therefore, only the Book
was fetched since the Blog
entity was marked with the
@Polymorphism(type = PolymorphismType.EXPLICIT)
annotation, which instructs Hibernate
to skip it when executing a polymorphic query against a non-mapped base class.
2.14. Mutability
Immutability can be specified for both entities and attributes.
Unfortunately mutability is an overloaded term. It can refer to either:
-
Whether the internal state of a value can be changed. In this sense, a
java.lang.Date
is considered
mutable because its internal state can be changed by callingDate#setTime
, whereasjava.lang.String
is considered immutable because its internal state cannot be changed. Hibernate uses this distinction
for numerous internal optimizations related to dirty checking and making copies. -
Whether the value is updateable in regard to the database. Hibernate can perform other optimizations
based on this distinction.
2.14.1. @Immutable
The @Immutable
annotation declares something immutable in the updateability sense. Mutable (updateable)
is the implicit condition.
@Immutable
is allowed on an entity, attribute,
AttributeConverter and UserType. Unfortunately, it
has slightly different impacts depending on where it is placed; see the linked sections for details.
2.14.2. Entity immutability
If a specific entity is immutable, it is good practice to mark it with the @Immutable
annotation.
Example 305. Immutable entity
@Entity(name = "Event")
@Immutable
public static class Event {
@Id
private Long id;
private Date createdOn;
private String message;
//Getters and setters are omitted for brevity
}
Internally, Hibernate is going to perform several optimizations, such as:
-
reducing memory footprint since there is no need to retain the loaded state for the dirty checking mechanism
-
speeding-up the Persistence Context flushing phase since immutable entities can skip the dirty checking process
Considering the following entity is persisted in the database:
Example 306. Persisting an immutable entity
Event event = new Event();
event.setId(1L);
event.setCreatedOn(new Date());
event.setMessage("Hibernate User Guide rocks!");
entityManager.persist(event);
When loading the entity and trying to change its state,
Hibernate will skip any modification, therefore no SQL UPDATE
statement is executed.
Example 307. The immutable entity ignores any update
Event event = entityManager.find(Event.class, 1L);
log.info("Change event message");
event.setMessage("Hibernate User Guide");
SELECT e.id AS id1_0_0_,
e.createdOn AS createdO2_0_0_,
e.message AS message3_0_0_
FROM event e
WHERE e.id = 1
-- Change event message
SELECT e.id AS id1_0_0_,
e.createdOn AS createdO2_0_0_,
e.message AS message3_0_0_
FROM event e
WHERE e.id = 1
@Mutability
is not allowed on an entity.
2.14.3. Attribute mutability
The @Immutable
annotation may also be used on attributes. The impact varies
slightly depending on the exact kind of attribute.
@Mutability
on an attribute applies the specified MutabilityPlan
to the attribute for handling
internal state changes in the values for the attribute.
Attribute immutability — basic
When applied to a basic attribute, @Immutable
implies immutability in both the updateable
and internal-state sense. E.g.
Example 308. Immutable basic attribute
@Immutable
private Date theDate;
Changes to the theDate
attribute are ignored.
Example 309. Immutable basic attribute change
final TheEntity theEntity = session.find( TheEntity.class, 1 );
// this change will be ignored
theEntity.theDate.setTime( Instant.EPOCH.toEpochMilli() );
Attribute immutability — embeddable
To be continued..
Attribute immutability — plural
Plural attributes (@ElementCollection
, @OneToMany`, @ManyToMany
and @ManyToAny
) may also
be annotated with @Immutable
.
- TIP
-
While most immutable changes are simply discarded, modifying an immutable collection will cause an exception.
Example 310. Persisting an immutable collection
Batch batch = new Batch();
batch.setId(1L);
batch.setName("Change request");
Event event1 = new Event();
event1.setId(1L);
event1.setCreatedOn(new Date());
event1.setMessage("Update Hibernate User Guide");
Event event2 = new Event();
event2.setId(2L);
event2.setCreatedOn(new Date());
event2.setMessage("Update Hibernate Getting Started Guide");
batch.getEvents().add(event1);
batch.getEvents().add(event2);
entityManager.persist(batch);
The Batch
entity is mutable. Only the events
collection is immutable.
For instance, we can still modify the entity name:
Example 311. Changing the mutable entity
Batch batch = entityManager.find(Batch.class, 1L);
log.info("Change batch name");
batch.setName("Proposed change request");
SELECT b.id AS id1_0_0_,
b.name AS name2_0_0_
FROM Batch b
WHERE b.id = 1
-- Change batch name
UPDATE batch
SET name = 'Proposed change request'
WHERE id = 1
However, when trying to modify the events
collection:
Example 312. Immutable collections cannot be modified
try {
Batch batch = entityManager.find( Batch.class, 1L );
batch.getEvents().clear();
}
catch (Exception e) {
log.error("Immutable collections cannot be modified");
}
jakarta.persistence.RollbackException: Error while committing the transaction
Caused by: jakarta.persistence.PersistenceException: org.hibernate.HibernateException:
Caused by: org.hibernate.HibernateException: changed an immutable collection instance: [
org.hibernate.orm.test.mapping.mutability.attribute.PluralAttributeMutabilityTest$Batch.events#1
]
Attribute immutability — entity
To be continued..
2.14.4. AttributeConverter mutability
Declaring @Mutability
on an AttributeConverter
applies the specified MutabilityPlan
to
all value mappings (attribute, collection element, etc.) to which the converter is applied.
Declaring @Immutable
on an AttributeConverter
is shorthand for declaring @Mutability
with an
immutable MutabilityPlan
.
2.14.5. UserType mutability
Similar to AttributeConverter both @Mutability
and @Immutable
may
be declared on a UserType
.
@Mutability
applies the specified MutabilityPlan
to all value mappings (attribute, collection element, etc.)
to which the UserType
is applied.
@Immutable
applies an immutable MutabilityPlan
to all value mappings (attribute, collection element, etc.)
to which the UserType
is applied.
2.14.6. @Mutability
MutabilityPlan
is the contract used by Hibernate to abstract mutability concerns, in the sense of internal state changes.
A Java type has an inherent MutabilityPlan
based on its JavaType#getMutabilityPlan
.
The @Mutability
annotation allows a specific MutabilityPlan
to be used and is allowed on an
attribute, AttributeConverter
and UserType
. When used on a AttributeConverter
or UserType
,
the specified MutabilityPlan
is effective for all basic values to which the AttributeConverter
or
UserType
is applied.
To understand the impact of internal-state mutability, consider the following entity:
Example 313. Basic mutability model
@Entity
public class MutabilityBaselineEntity {
@Id
private Integer id;
@Basic
private String name;
@Basic
private Date activeTimestamp;
}
When dealing with an inherently immutable value, such as a String
, there is only one way to
update the value:
Example 314. Changing immutable value
Session session = getSession();
MutabilityBaselineEntity entity = session.find( MutabilityBaselineEntity.class, 1 );
entity.setName( "new name" );
During flush, this change will make the entity «dirty» and the changes will be written (UPDATE) to
the database.
When dealing with mutable values, however, Hibernate must be aware of both ways to change the value. First, like
with the immutable value, we can set the new value:
Example 315. Changing mutable value — setting
Session session = getSession();
MutabilityBaselineEntity entity = session.find( MutabilityBaselineEntity.class, 1 );
entity.setActiveTimestamp( now() );
We can also mutate the existing value:
Example 316. Changing mutable value — mutating
Session session = getSession();
MutabilityBaselineEntity entity = session.find( MutabilityBaselineEntity.class, 1 );
entity.getActiveTimestamp().setTime( now().getTime() );
This mutating example has the same effect as the setting example — they each will make the entity dirty.
2.15. Customizing the domain model
For cases where Hibernate does not provide a built-in way to configure the domain
model mapping based on requirements, it provides a very broad and flexible
way to adjust the mapping model through its «boot-time model» (defined in
the org.hibernate.mapping
package) using its @AttributeBinderType
meta
annotation and corresponding AttributeBinder
contract.
An example:
Example 317. AttributeBinder example
/**
* Custom annotation applying 'Y'/'N' storage semantics to a boolean.
*
* The important piece here is `@AttributeBinderType`
*/
@Target({METHOD,FIELD})
@Retention(RUNTIME)
@AttributeBinderType( binder = YesNoBinder.class )
public @interface YesNo {
}
/**
* The actual binder responsible for configuring the model objects
*/
public class YesNoBinder implements AttributeBinder<YesNo> {
@Override
public void bind(
YesNo annotation,
MetadataBuildingContext buildingContext,
PersistentClass persistentClass,
Property property) {
( (SimpleValue) property.getValue() ).setJpaAttributeConverterDescriptor(
new InstanceBasedConverterDescriptor(
YesNoConverter.INSTANCE,
buildingContext.getBootstrapContext().getClassmateContext()
)
);
}
}
The important thing to take away here is that both @YesNo
and YesNoBinder
are custom, user-written
code. Hibernate has no inherent understanding of what a @YesNo
does or is. It only understands that
it has the @AttributeBinderType
meta-annotation and knows how to apply that through the corresponding
YesNoBinder
.
Notice also that @AttributeBinderType
provides a type-safe way to perform configuration because
the AttributeBinder
(YesNoBinder
) is handed the custom annotation (@YesNo
) to grab its configured
attributes. @YesNo
does not provide any attributes, but it easily could. Whatever YesNoBinder
supports.
3. Bootstrap
The term bootstrapping refers to initializing and starting a software component.
In Hibernate, we are specifically talking about the process of building a fully functional SessionFactory
instance or EntityManagerFactory
instance, for Jakarta Persistence.
The process is very different for each.
During the bootstrap process, you might want to customize Hibernate behavior so make sure you check the Configuration Settings section as well. |
3.1. Native Bootstrapping
This section discusses the process of bootstrapping a Hibernate SessionFactory
.
Specifically, it addresses the bootstrapping APIs.
For a discussion of the legacy bootstrapping API, see Legacy Bootstrapping.
3.1.1. Building the ServiceRegistry
The first step in native bootstrapping is the building of a ServiceRegistry
holding the services Hibernate will need during bootstrapping and at run time.
Actually, we are concerned with building 2 different ServiceRegistries.
First is the org.hibernate.boot.registry.BootstrapServiceRegistry
.
The BootstrapServiceRegistry
is intended to hold services that Hibernate needs at both bootstrap and run time.
This boils down to 3 services:
org.hibernate.boot.registry.classloading.spi.ClassLoaderService
-
which controls how Hibernate interacts with
ClassLoader
s. org.hibernate.integrator.spi.IntegratorService
-
which controls the management and discovery of
org.hibernate.integrator.spi.Integrator
instances. org.hibernate.boot.registry.selector.spi.StrategySelector
-
which controls how Hibernate resolves implementations of various strategy contracts.
This is a very powerful service, but a full discussion of it is beyond the scope of this guide.
If you are ok with the default behavior of Hibernate in regards to these |
If you wish to alter how the BootstrapServiceRegistry
is built, that is controlled through the org.hibernate.boot.registry.BootstrapServiceRegistryBuilder
:
Example 318. Controlling BootstrapServiceRegistry
building
BootstrapServiceRegistryBuilder bootstrapRegistryBuilder =
new BootstrapServiceRegistryBuilder();
// add a custom ClassLoader
bootstrapRegistryBuilder.applyClassLoader(customClassLoader);
// manually add an Integrator
bootstrapRegistryBuilder.applyIntegrator(customIntegrator);
BootstrapServiceRegistry bootstrapRegistry = bootstrapRegistryBuilder.build();
The services of the |
The second ServiceRegistry is the org.hibernate.boot.registry.StandardServiceRegistry
.
You will almost always need to configure the StandardServiceRegistry
, which is done through org.hibernate.boot.registry.StandardServiceRegistryBuilder
:
Example 319. Building a BootstrapServiceRegistryBuilder
// An example using an implicitly built BootstrapServiceRegistry
StandardServiceRegistryBuilder standardRegistryBuilder =
new StandardServiceRegistryBuilder();
// An example using an explicitly built BootstrapServiceRegistry
BootstrapServiceRegistry bootstrapRegistry =
new BootstrapServiceRegistryBuilder().build();
StandardServiceRegistryBuilder standardRegistryBuilder =
new StandardServiceRegistryBuilder(bootstrapRegistry);
A StandardServiceRegistry
is also highly configurable via the StandardServiceRegistryBuilder API.
See the StandardServiceRegistryBuilder
Javadocs for more details.
Some specific methods of interest:
3.1.2. Event Listener registration
The main use cases for an org.hibernate.integrator.spi.Integrator
right now are registering event listeners.
Example 321. Configuring an event listener
public class MyIntegrator implements Integrator {
@Override
public void integrate(
Metadata metadata,
BootstrapContext bootstrapContext,
SessionFactoryImplementor sessionFactory) {
// As you might expect, an EventListenerRegistry is the thing with which event
// listeners are registered
// It is a service so we look it up using the service registry
final EventListenerRegistry eventListenerRegistry =
bootstrapContext.getServiceRegistry().getService(EventListenerRegistry.class);
// If you wish to have custom determination and handling of "duplicate" listeners,
// you would have to add an implementation of the
// org.hibernate.event.service.spi.DuplicationStrategy contract like this
eventListenerRegistry.addDuplicationStrategy(new CustomDuplicationStrategy());
// EventListenerRegistry defines 3 ways to register listeners:
// 1) This form overrides any existing registrations with
eventListenerRegistry.setListeners(EventType.AUTO_FLUSH,
DefaultAutoFlushEventListener.class);
// 2) This form adds the specified listener(s) to the beginning of the listener chain
eventListenerRegistry.prependListeners(EventType.PERSIST,
DefaultPersistEventListener.class);
// 3) This form adds the specified listener(s) to the end of the listener chain
eventListenerRegistry.appendListeners(EventType.MERGE,
DefaultMergeEventListener.class);
}
@Override
public void disintegrate(
SessionFactoryImplementor sessionFactory,
SessionFactoryServiceRegistry serviceRegistry) {
}
}
3.1.3. Building the Metadata
The second step in native bootstrapping is the building of an org.hibernate.boot.Metadata
object containing the parsed representations of an application domain model and its mapping to a database.
The first thing we obviously need to build a parsed representation is the source information to be parsed (annotated classes, hbm.xml
files, orm.xml
files).
This is the purpose of org.hibernate.boot.MetadataSources
.
MetadataSources
has many other methods as well. Explore its API and Javadocs for more information.
Also, all methods on MetadataSources
offer fluent-style call chaining::
Once we have the sources of mapping information defined, we need to build the Metadata
object.
If you are ok with the default behavior in building the Metadata then you can simply call the buildMetadata
method of the MetadataSources
.
Notice that a |
However, if you wish to adjust the process of building Metadata
from MetadataSources
,
you will need to use the MetadataBuilder
as obtained via MetadataSources#getMetadataBuilder
.
MetadataBuilder
allows a lot of control over the Metadata
building process.
See its Javadocs for full details.
3.1.4. Building the SessionFactory
The final step in native bootstrapping is to build the SessionFactory
itself.
Much like discussed above, if you are ok with the default behavior of building a SessionFactory
from a Metadata
reference, you can simply call the buildSessionFactory
method on the Metadata
object.
However, if you would like to adjust that building process, you will need to use SessionFactoryBuilder
as obtained via Metadata#getSessionFactoryBuilder
. Again, see its Javadocs for more details.
Example 324. Native Bootstrapping — Putting it all together
StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
.configure("org/hibernate/example/hibernate.cfg.xml")
.build();
Metadata metadata = new MetadataSources(standardRegistry)
.addAnnotatedClass(MyEntity.class)
.addAnnotatedClassName("org.hibernate.example.Customer")
.addResource("org/hibernate/example/Order.hbm.xml")
.addResource("org/hibernate/example/Product.orm.xml")
.getMetadataBuilder()
.applyImplicitNamingStrategy(ImplicitNamingStrategyJpaCompliantImpl.INSTANCE)
.build();
SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
.applyBeanManager(getBeanManager())
.build();
The bootstrapping API is quite flexible, but in most cases it makes the most sense to think of it as a 3 step process:
-
Build the
StandardServiceRegistry
-
Build the
Metadata
-
Use those 2 to build the
SessionFactory
Example 325. Building SessionFactory
via SessionFactoryBuilder
StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
.configure("org/hibernate/example/hibernate.cfg.xml")
.build();
Metadata metadata = new MetadataSources(standardRegistry)
.addAnnotatedClass(MyEntity.class)
.addAnnotatedClassName("org.hibernate.example.Customer")
.addResource("org/hibernate/example/Order.hbm.xml")
.addResource("org/hibernate/example/Product.orm.xml")
.getMetadataBuilder()
.applyImplicitNamingStrategy(ImplicitNamingStrategyJpaCompliantImpl.INSTANCE)
.build();
SessionFactoryBuilder sessionFactoryBuilder = metadata.getSessionFactoryBuilder();
// Supply a SessionFactory-level Interceptor
sessionFactoryBuilder.applyInterceptor(new CustomSessionFactoryInterceptor());
// Add a custom observer
sessionFactoryBuilder.addSessionFactoryObservers(new CustomSessionFactoryObserver());
// Apply a CDI BeanManager (for JPA event listeners)
sessionFactoryBuilder.applyBeanManager(getBeanManager());
SessionFactory sessionFactory = sessionFactoryBuilder.build();
3.2. Jakarta Persistence Bootstrapping
Bootstrapping Hibernate as a Jakarta Persistence provider can be done in a Jakarta Persistence-spec compliant manner or using a proprietary bootstrapping approach.
The standardized approach has some limitations in certain environments, but aside from those, it is highly recommended that you use Jakarta Persistence-standardized bootstrapping.
3.2.1. Jakarta Persistence-compliant bootstrapping
In Jakarta Persistence, we are ultimately interested in bootstrapping a jakarta.persistence.EntityManagerFactory
instance.
The Jakarta Persistence specification defines two primary standardized bootstrap approaches depending on how the application intends to access the jakarta.persistence.EntityManager
instances from an EntityManagerFactory
.
It uses the terms EE and SE for these two approaches, but those terms are very misleading in this context.
What the Jakarta Persistence spec calls EE bootstrapping implies the existence of a container (EE, OSGi, etc), who’ll manage and inject the persistence context on behalf of the application.
What it calls SE bootstrapping is everything else. We will use the terms container-bootstrapping and application-bootstrapping in this guide.
For compliant container-bootstrapping, the container will build an EntityManagerFactory
for each persistent-unit defined in the META-INF/persistence.xml
configuration file
and make that available to the application for injection via the jakarta.persistence.PersistenceUnit
annotation or via JNDI lookup.
Example 326. Injecting the default EntityManagerFactory
@PersistenceUnit
private EntityManagerFactory emf;
Or, in case you have multiple Persistence Units (e.g. multiple persistence.xml
configuration files),
you can inject a specific EntityManagerFactory
by Unit name:
Example 327. Injecting a specific EntityManagerFactory
@PersistenceUnit(
unitName = "CRM"
)
private EntityManagerFactory entityManagerFactory;
The META-INF/persistence.xml
file looks as follows:
Example 328. META-INF/persistence.xml configuration file
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
version="2.1">
<persistence-unit name="CRM">
<description>
Persistence unit for Hibernate User Guide
</description>
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<class>org.hibernate.documentation.userguide.Document</class>
<properties>
<property name="jakarta.persistence.jdbc.driver"
value="org.h2.Driver" />
<property name="jakarta.persistence.jdbc.url"
value="jdbc:h2:mem:db1;DB_CLOSE_DELAY=-1" />
<property name="jakarta.persistence.jdbc.user"
value="sa" />
<property name="jakarta.persistence.jdbc.password"
value="" />
<property name="hibernate.show_sql"
value="true" />
<property name="hibernate.hbm2ddl.auto"
value="update" />
</properties>
</persistence-unit>
</persistence>
For compliant application-bootstrapping, rather than the container building the EntityManagerFactory
for the application, the application builds the EntityManagerFactory
itself using the jakarta.persistence.Persistence
bootstrap class.
The application creates an EntityManagerFactory
by calling the createEntityManagerFactory
method:
Example 329. Application bootstrapped EntityManagerFactory
// Create an EMF for our CRM persistence-unit.
EntityManagerFactory emf = Persistence.createEntityManagerFactory("CRM");
To inject the default Persistence Context, you can use the @PersistenceContext
annotation.
Example 330. Inject the default EntityManager
@PersistenceContext
private EntityManager em;
To inject a specific Persistence Context,
you can use the @PersistenceContext
annotation,
and you can even pass EntityManager
-specific properties using the
@PersistenceProperty
annotation.
Example 331. Inject a configurable EntityManager
@PersistenceContext(
unitName = "CRM",
properties = {
@PersistenceProperty(
name="org.hibernate.flushMode",
value= "MANUAL"
)
}
)
private EntityManager entityManager;
If you would like additional details on accessing and using |
3.2.2. Externalizing XML mapping files
Jakarta Persistence offers two mapping options:
-
annotations
-
XML mappings
Although annotations are much more common, there are projects where XML mappings are preferred.
You can even mix annotations and XML mappings so that you can override annotation mappings with XML configurations that can be easily changed without recompiling the project source code.
This is possible because if there are two conflicting mappings, the XML mappings take precedence over its annotation counterpart.
The Jakarta Persistence specification requires the XML mappings to be located on the classpath:
An object/relational mapping XML file named
orm.xml
may be specified in theMETA-INF
directory in the root of the persistence unit or in theMETA-INF
directory of any jar file referenced by thepersistence.xml
.Alternatively, or in addition, one or more mapping files may be referenced by the mapping-file elements of the persistence-unit element. These mapping files may be present anywhere on the classpath.
— Section 8.2.1.6.2 of the Jakarta Persistence
Therefore, the mapping files can reside in the application jar artifacts, or they can be stored in an external folder location with the cogitation that that location be included in the classpath.
Hibernate is more lenient in this regard so you can use any external location even outside of the application configured classpath.
Example 332. META-INF/persistence.xml configuration file for external XML mappings
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
version="2.1">
<persistence-unit name="CRM">
<description>
Persistence unit for Hibernate User Guide
</description>
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<mapping-file>file:///etc/opt/app/mappings/orm.xml</mapping-file>
<properties>
<property name="jakarta.persistence.jdbc.driver"
value="org.h2.Driver" />
<property name="jakarta.persistence.jdbc.url"
value="jdbc:h2:mem:db1;DB_CLOSE_DELAY=-1" />
<property name="jakarta.persistence.jdbc.user"
value="sa" />
<property name="jakarta.persistence.jdbc.password"
value="" />
<property name="hibernate.show_sql"
value="true" />
<property name="hibernate.hbm2ddl.auto"
value="update" />
</properties>
</persistence-unit>
</persistence>
In the persistence.xml
configuration file above, the orm.xml
XML file containing all Jakarta Persistence entity mappings is located in the /etc/opt/app/mappings/
folder.
3.2.3. Configuring the SessionFactory
Metadata
via the Jakarta Persistence bootstrap
As previously seen, the Hibernate native bootstrap mechanism allows you to customize a great variety of configurations which are passed via the Metadata
object.
When using Hibernate as a Jakarta Persistence provider, the EntityManagerFactory
is backed by a SessionFactory
. For this reason, you might still want to use the Metadata
object to pass various settings which cannot be supplied via the standard Hibernate configuration settings.
For this reason, you can use the
MetadataBuilderContributor
class as you can see in the following examples.
org.hibernate.orm.test.bootstrap.spi.metadatabuildercontributor
The above MetadataBuilderContributor
is used to register a SqlFuction
which is not defined by the currently running Hibernate Dialect
, but which we need to reference in our JPQL queries.
By having access to the
MetadataBuilder
class that’s used by the underlying SessionFactory
, the Jakarta Persistence bootstrap becomes just as flexible as the Hibernate native bootstrap mechanism.
You can then pass the custom MetadataBuilderContributor
via the hibernate.metadata_builder_contributor
configuration property as explained in the Configuration chapter.
4. Schema Generation
Hibernate allows you to generate the database from the entity mappings.
Although the automatic schema generation is very useful for testing and prototyping purposes, in a production environment, |
Traditionally, the process of generating schema from entity mapping has been called HBM2DDL
.
To get a list of Hibernate-native and Jakarta Persistence-specific configuration properties consider reading the Configurations section.
Considering the following Domain Model:
Example 334. Schema generation Domain Model
@Entity(name = "Customer")
public class Customer {
@Id
private Integer id;
private String name;
@Basic(fetch = FetchType.LAZY)
private UUID accountsPayableXrefId;
@Lob
@Basic(fetch = FetchType.LAZY)
@LazyGroup("lobs")
private Blob image;
//Getters and setters are omitted for brevity
}
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
@OneToMany(mappedBy = "author")
private List<Book> books = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
@NaturalId
private String isbn;
@ManyToOne
private Person author;
//Getters and setters are omitted for brevity
}
If the hibernate.hbm2ddl.auto
configuration is set to create
, Hibernate is going to generate the following database schema:
Example 335. Auto-generated database schema
create table Customer (
id integer not null,
accountsPayableXrefId binary,
image blob,
name varchar(255),
primary key (id)
)
create table Book (
id bigint not null,
isbn varchar(255),
title varchar(255),
author_id bigint,
primary key (id)
)
create table Person (
id bigint not null,
name varchar(255),
primary key (id)
)
alter table Book
add constraint UK_u31e1frmjp9mxf8k8tmp990i unique (isbn)
alter table Book
add constraint FKrxrgiajod1le3gii8whx2doie
foreign key (author_id)
references Person
4.1. Importing script files
To customize the schema generation process, the hibernate.hbm2ddl.import_files
configuration property must be used to provide other scripts files that Hibernate can use when the SessionFactory
is started.
For instance, considering the following schema-generation.sql
import file:
Example 336. Schema generation import file
create sequence book_sequence start with 1 increment by 1
If we configure Hibernate to import the script above:
Example 337. Enabling schema generation import file
<property
name="hibernate.hbm2ddl.import_files"
value="schema-generation.sql" />
Hibernate is going to execute the script file after the schema is automatically generated.
4.2. Database objects
Hibernate allows you to customize the schema generation process via the HBM database-object
element.
Considering the following HBM mapping:
Example 338. Schema generation HBM database-object
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
<database-object>
<create>
CREATE OR REPLACE FUNCTION sp_count_books(
IN authorId bigint,
OUT bookCount bigint)
RETURNS bigint AS
$BODY$
BEGIN
SELECT COUNT(*) INTO bookCount
FROM book
WHERE author_id = authorId;
END;
$BODY$
LANGUAGE plpgsql;
</create>
<drop></drop>
<dialect-scope name="org.hibernate.dialect.PostgreSQLDialect" />
</database-object>
</hibernate-mapping>
When the SessionFactory
is bootstrapped, Hibernate is going to execute the database-object
, therefore creating the sp_count_books
function.
4.3. Database-level checks
Hibernate offers the @Check
annotation so that you can specify an arbitrary SQL CHECK constraint which can be defined as follows:
Example 339. Database check entity mapping example
@Entity(name = "Book")
@Check(name = "ValidIsbn", constraints = "CASE WHEN isbn IS NOT NULL THEN LENGTH(isbn) = 13 ELSE true END")
@SecondaryTable(name = "BookEdition")
@Check(name = "PositiveEdition", constraints = "edition > 0")
public static class Book {
@Id
private Long id;
private String title;
@NaturalId
private String isbn;
private Double price;
@Column(table = "BookEdition")
private int edition = 1;
@Formula("edition + 1")
private int nextEdition = 2;
@Column(table = "BookEdition")
private LocalDate editionDate;
//Getters and setters omitted for brevity
}
Now, if you try to add a Book
entity with an isbn
attribute whose length is not 13 characters,
a ConstraintViolationException
is going to be thrown.
Example 340. Database check failure example
Book book = new Book();
book.setId(1L);
book.setPrice(49.99d);
book.setTitle("High-Performance Java Persistence");
book.setIsbn("11-11-2016");
entityManager.persist(book);
INSERT INTO Book (isbn, price, title, id)
VALUES ('11-11-2016', 49.99, 'High-Performance Java Persistence', 1)
-- WARN SqlExceptionHelper:129 - SQL Error: 0, SQLState: 23514
-- ERROR SqlExceptionHelper:131 - ERROR: new row for relation "book" violates check constraint "book_isbn_check"
4.4. Default value for a database column
With Hibernate, you can specify a default value for a given database column using the @ColumnDefault
annotation.
Example 341. @ColumnDefault
mapping example
@Entity(name = "Person")
@DynamicInsert
public static class Person {
@Id
private Long id;
@ColumnDefault("'N/A'")
private String name;
@ColumnDefault("-1")
private Long clientId;
//Getter and setters omitted for brevity
}
CREATE TABLE Person (
id BIGINT NOT NULL,
clientId BIGINT DEFAULT -1,
name VARCHAR(255) DEFAULT 'N/A',
PRIMARY KEY (id)
)
In the mapping above, both the name
and clientId
table columns have a DEFAULT
value.
The |
This way, when the name
and or clientId
attribute is null, the database will set them according to their declared default values.
Example 342. @ColumnDefault
mapping example
doInJPA(this::entityManagerFactory, entityManager -> {
Person person = new Person();
person.setId(1L);
entityManager.persist(person);
});
doInJPA(this::entityManagerFactory, entityManager -> {
Person person = entityManager.find(Person.class, 1L);
assertEquals("N/A", person.getName());
assertEquals(Long.valueOf(-1L), person.getClientId());
});
INSERT INTO Person (id) VALUES (?)
If the column value should be generated not only when a row is inserted, but also when it’s updated, the |
4.5. Columns unique constraint
The @UniqueConstraint
annotation is used to specify a unique constraint to be included by the automated schema generator for the primary or secondary table associated with the current annotated entity.
Considering the following entity mapping, Hibernate generates the unique constraint DDL when creating the database schema:
Example 343. @UniqueConstraint
mapping example
@Entity
@Table(
name = "book",
uniqueConstraints = @UniqueConstraint(
name = "uk_book_title_author",
columnNames = {
"title",
"author_id"
}
)
)
public static class Book {
@Id
@GeneratedValue
private Long id;
private String title;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(
name = "author_id",
foreignKey = @ForeignKey(name = "fk_book_author_id")
)
private Author author;
//Getter and setters omitted for brevity
}
@Entity
@Table(name = "author")
public static class Author {
@Id
@GeneratedValue
private Long id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
//Getter and setters omitted for brevity
}
create table author (
id bigint not null,
first_name varchar(255),
last_name varchar(255),
primary key (id)
)
create table book (
id bigint not null,
title varchar(255),
author_id bigint,
primary key (id)
)
alter table book
add constraint uk_book_title_author
unique (title, author_id)
alter table book
add constraint fk_book_author_id
foreign key (author_id)
references author
With the uk_book_title_author
unique constraint in place,
it’s no longer possible to add two books with the same title and for the same author.
Example 344. @UniqueConstraintTest
persist example
Author _author = doInJPA(this::entityManagerFactory, entityManager -> {
Author author = new Author();
author.setFirstName("Vlad");
author.setLastName("Mihalcea");
entityManager.persist(author);
Book book = new Book();
book.setTitle("High-Performance Java Persistence");
book.setAuthor(author);
entityManager.persist(book);
return author;
});
try {
doInJPA(this::entityManagerFactory, entityManager -> {
Book book = new Book();
book.setTitle("High-Performance Java Persistence");
book.setAuthor(_author);
entityManager.persist(book);
});
}
catch (Exception expected) {
assertNotNull(ExceptionUtil.findCause(expected, ConstraintViolationException.class));
}
insert
into
author
(first_name, last_name, id)
values
(?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [Vlad]
-- binding parameter [2] as [VARCHAR] - [Mihalcea]
-- binding parameter [3] as [BIGINT] - [1]
insert
into
book
(author_id, title, id)
values
(?, ?, ?)
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [BIGINT] - [2]
insert
into
book
(author_id, title, id)
values
(?, ?, ?)
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [BIGINT] - [3]
-- SQL Error: 23505, SQLState: 23505
-- Unique index or primary key violation: "UK_BOOK_TITLE_AUTHOR_INDEX_1 ON PUBLIC.BOOK(TITLE, AUTHOR_ID) VALUES ( /* key:1 */ 3, 'High-Performance Java Persistence', 1)";
The second INSERT statement fails because of the unique constraint violation.
4.6. Columns index
The @Index
annotation is used by the automated schema generation tool to create a database index.
Considering the following entity mapping. Hibernate generates the index when creating the database schema:
Example 345. @Index
mapping example
@Entity
@Table(
name = "author",
indexes = @Index(
name = "idx_author_first_last_name",
columnList = "first_name, last_name",
unique = false
)
)
public static class Author {
@Id
@GeneratedValue
private Long id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
//Getter and setters omitted for brevity
}
create table author (
id bigint not null,
first_name varchar(255),
last_name varchar(255),
primary key (id)
)
create index idx_author_first_last_name
on author (first_name, last_name)
5. Persistence Context
Both the org.hibernate.Session
API and jakarta.persistence.EntityManager
API represent a context for dealing with persistent data.
This concept is called a persistence context
.
Persistent data has a state in relation to both a persistence context and the underlying database.
transient
-
the entity has just been instantiated and is not associated with a persistence context.
It has no persistent representation in the database and typically no identifier value has been assigned (unless the assigned generator was used). managed
orpersistent
-
the entity has an associated identifier and is associated with a persistence context.
It may or may not physically exist in the database yet. detached
-
the entity has an associated identifier but is no longer associated with a persistence context (usually because the persistence context was closed or the instance was evicted from the context)
removed
-
the entity has an associated identifier and is associated with a persistence context, however, it is scheduled for removal from the database.
Much of the org.hibernate.Session
and jakarta.persistence.EntityManager
methods deal with moving entities among these states.
5.1. Accessing Hibernate APIs from Jakarta Persistence
Jakarta Persistence defines an incredibly useful method to allow applications access to the APIs of the underlying provider.
Example 346. Accessing Hibernate APIs from Jakarta Persistence
Session session = entityManager.unwrap(Session.class);
SessionImplementor sessionImplementor = entityManager.unwrap(SessionImplementor.class);
SessionFactory sessionFactory = entityManager.getEntityManagerFactory().unwrap(SessionFactory.class);
5.2. Bytecode Enhancement
Hibernate «grew up» not supporting bytecode enhancement at all.
At that time, Hibernate only supported proxy-based alternative for lazy loading and always used diff-based dirty calculation.
Hibernate 3.x saw the first attempts at bytecode enhancement support in Hibernate.
We consider those initial attempts (up until 5.0) completely as an incubation.
The support for bytecode enhancement in 5.0 onward is what we are discussing here.
See Bytecode Enhancement for discussion of performing enhancement.
5.2.1. Lazy attribute loading
Think of this as partial loading support.
Essentially, you can tell Hibernate that only part(s) of an entity should be loaded upon fetching from the database and when the other part(s) should be loaded as well.
Note that this is very much different from the proxy-based idea of lazy loading which is entity-centric where the entity’s state is loaded at once as needed.
With bytecode enhancement, individual attributes or groups of attributes are loaded as needed.
Lazy attributes can be designated to be loaded together, and this is called a «lazy group».
By default, all singular attributes are part of a single group, meaning that when one lazy singular attribute is accessed all lazy singular attributes are loaded.
Lazy plural attributes, by default, are each a lazy group by themselves.
This behavior is explicitly controllable through the @org.hibernate.annotations.LazyGroup
annotation.
Example 347. @LazyGroup
example
@Entity
public class Customer {
@Id
private Integer id;
private String name;
@Basic(fetch = FetchType.LAZY)
private UUID accountsPayableXrefId;
@Lob
@Basic(fetch = FetchType.LAZY)
@LazyGroup("lobs")
private Blob image;
//Getters and setters are omitted for brevity
}
In the above example, we have 2 lazy attributes: accountsPayableXrefId
and image
.
Each is part of a different fetch group (accountsPayableXrefId is part of the default fetch group),
which means that accessing accountsPayableXrefId
will not force the loading of the image
attribute, and vice-versa.
As a hopefully temporary legacy hold-over, it is currently required that all lazy singular associations (many-to-one and one-to-one) also include |
5.2.2. In-line dirty tracking
Historically Hibernate only supported diff-based dirty calculation for determining which entities in a persistence context have changed.
This essentially means that Hibernate would keep track of the last known state of an entity in regards to the database (typically the last read or write).
Then, as part of flushing the persistence context, Hibernate would walk every entity associated with the persistence context and check its current state against that «last known database state».
This is by far the most thorough approach to dirty checking because it accounts for data-types that can change their internal state (java.util.Date
is the prime example of this).
However, in a persistence context with a large number of associated entities, it can also be a performance-inhibiting approach.
If your application does not need to care about «internal state changing data-type» use cases, bytecode-enhanced dirty tracking might be a worthwhile alternative to consider, especially in terms of performance.
In this approach Hibernate will manipulate the bytecode of your classes to add «dirty tracking» directly to the entity, allowing the entity itself to keep track of which of its attributes have changed.
During the flush time, Hibernate asks your entity what has changed rather than having to perform the state-diff calculations.
5.2.3. Bidirectional association management
Hibernate strives to keep your application as close to «normal Java usage» (idiomatic Java) as possible.
Consider a domain model with a normal Person
/Book
bidirectional association:
Example 348. Bidirectional association
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
@OneToMany(mappedBy = "author")
private List<Book> books = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
@NaturalId
private String isbn;
@ManyToOne
private Person author;
//Getters and setters are omitted for brevity
}
Example 349. Incorrect normal Java usage
Person person = new Person();
person.setName("John Doe");
Book book = new Book();
person.getBooks().add(book);
try {
book.getAuthor().getName();
}
catch (NullPointerException expected) {
// This blows up (NPE) in normal Java usage
}
This blows up in normal Java usage. The correct normal Java usage is:
Example 350. Correct normal Java usage
Person person = new Person();
person.setName("John Doe");
Book book = new Book();
person.getBooks().add(book);
book.setAuthor(person);
book.getAuthor().getName();
Bytecode-enhanced bi-directional association management makes that first example work by managing the «other side» of a bi-directional association whenever one side is manipulated.
5.2.4. Internal performance optimizations
Additionally, we use the enhancement process to add some additional code that allows us to optimize certain performance
characteristics of the persistence context. These are hard to discuss without diving into a discussion of Hibernate internals.
5.3. Making entities persistent
Once you’ve created a new entity instance (using the standard new
operator) it is in new
state.
You can make it persistent by associating it to either an org.hibernate.Session
or a jakarta.persistence.EntityManager
.
Example 351. Making an entity persistent with Jakarta Persistence
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
entityManager.persist(person);
Example 352. Making an entity persistent with Hibernate API
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
session.persist(person);
org.hibernate.Session
also has a method named persist which follows the exact semantics defined in the Jakarta Persistence specification for the persist method.
It is this org.hibernate.Session
method to which the Hibernate jakarta.persistence.EntityManager
implementation delegates.
If the DomesticCat
entity type has a generated identifier, the value is associated with the instance when the save or persist is called.
If the identifier is not automatically generated, the manually assigned (usually natural) key value has to be set on the instance before the save or persist methods are called.
5.4. Deleting (removing) entities
Entities can also be deleted.
Example 353. Deleting an entity with Jakarta Persistence
entityManager.remove(person);
Example 354. Deleting an entity with the Hibernate API
Hibernate itself can handle deleting entities in detached state. The implication here is that the entity instance passed to the |
5.5. Obtain an entity reference without initializing its data
Sometimes referred to as lazy loading, the ability to obtain a reference to an entity without having to load its data is hugely important.
The most common case being the need to create an association between an entity and another existing entity.
Example 355. Obtaining an entity reference without initializing its data with Jakarta Persistence
Book book = new Book();
book.setAuthor(entityManager.getReference(Person.class, personId));
Example 356. Obtaining an entity reference without initializing its data with Hibernate API
Book book = new Book();
book.setId(1L);
book.setIsbn("123-456-7890");
entityManager.persist(book);
book.setAuthor(session.getReference(Person.class, personId));
The above works on the assumption that the entity is defined to allow lazy loading, generally through use of runtime proxies.
In both cases an exception will be thrown later if the given entity does not refer to actual database state when the application attempts to use the returned proxy in any way that requires access to its data.
Unless the entity class is declared |
5.6. Obtain an entity with its data initialized
It is also quite common to want to obtain an entity along with its data (e.g. like when we need to display it in the UI).
Example 357. Obtaining an entity reference with its data initialized with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
Example 358. Obtaining an entity reference with its data initialized with Hibernate API
Person person = session.get(Person.class, personId);
Example 359. Obtaining an entity reference with its data initialized using the byId()
Hibernate API
Person person = session.byId(Person.class).load(personId);
In both cases null is returned if no matching database row was found.
It’s possible to return a Java 8 Optional
as well:
Example 360. Obtaining an Optional entity reference with its data initialized using the byId()
Hibernate API
Optional<Person> optionalPerson = session.byId(Person.class).loadOptional(personId);
5.7. Obtain multiple entities by their identifiers
If you want to load multiple entities by providing their identifiers, calling the EntityManager#find
method multiple times is not only inconvenient,
but also inefficient.
While the Jakarta Persistence standard does not support retrieving multiple entities at once, other than running a JPQL or Criteria API query,
Hibernate offers this functionality via the
byMultipleIds
method of the Hibernate Session
.
The byMultipleIds
method returns a
MultiIdentifierLoadAccess
which you can use to customize the multi-load request.
The MultiIdentifierLoadAccess
interface provides several methods which you can use to
change the behavior of the multi-load call:
enableOrderedReturn(boolean enabled)
-
This setting controls whether the returned
List
is ordered and positional in relation to the
incoming ids. If enabled (the default), the returnList
is ordered and
positional relative to the incoming ids. In other words, a request to
multiLoad([2,1,3])
will return[Entity#2, Entity#1, Entity#3]
.An important distinction is made here in regards to the handling of
unknown entities depending on this «ordered return» setting.
If enabled, a null is inserted into theList
at the proper position(s).
If disabled, the nulls are not put into the return List.In other words, consumers of the returned ordered List would need to be able to handle null elements.
enableSessionCheck(boolean enabled)
-
This setting, which is disabled by default, tells Hibernate to check the first-level cache (a.k.a
Session
or Persistence Context) first and, if the entity is found and already managed by the HibernateSession
, the cached entity will be added to the returnedList
, therefore skipping it from being fetched via the multi-load query. enableReturnOfDeletedEntities(boolean enabled)
-
This setting instructs Hibernate if the multi-load operation is allowed to return entities that were deleted by the current Persistence Context. A deleted entity is one which has been passed to this
Session.delete
orSession.remove
method, but theSession
was not flushed yet, meaning that the
associated row was not deleted in the database table.The default behavior is to handle them as null in the return (see
enableOrderedReturn
).
When enabled, the result set will contain deleted entities.
When disabled (which is the default behavior), deleted entities are not included in the returningList
. with(LockOptions lockOptions)
-
This setting allows you to pass a given
LockOptions
mode to the multi-load query. with(CacheMode cacheMode)
-
This setting allows you to pass a given
CacheMode
strategy so that we can load entities from the second-level cache, therefore skipping the cached entities from being fetched via the multi-load query. withBatchSize(int batchSize)
-
This setting allows you to specify a batch size for loading the entities (e.g. how many at a time).
The default is to use a batch sizing strategy defined by the
Dialect.getDefaultBatchLoadSizingStrategy()
method.Any greater-than-one value here will override that default behavior.
with(RootGraph<T> graph)
-
The
RootGraph
is a Hibernate extension to the Jakarta PersistenceEntityGraph
contract,
and this method allows you to pass a specificRootGraph
to the multi-load query
so that it can fetch additional relationships of the current loading entity.
Now, assuming we have 3 Person
entities in the database, we can load all of them with a single call
as illustrated by the following example:
Example 361. Loading multiple entities using the byMultipleIds()
Hibernate API
Session session = entityManager.unwrap( Session.class );
List<Person> persons = session
.byMultipleIds( Person.class )
.multiLoad( 1L, 2L, 3L );
assertEquals( 3, persons.size() );
List<Person> samePersons = session
.byMultipleIds( Person.class )
.enableSessionCheck( true )
.multiLoad( 1L, 2L, 3L );
assertEquals( persons, samePersons );
SELECT p.id AS id1_0_0_,
p.name AS name2_0_0_
FROM Person p
WHERE p.id IN ( 1, 2, 3 )
Notice that only one SQL SELECT statement was executed since the second call uses the
enableSessionCheck
method of the MultiIdentifierLoadAccess
to instruct Hibernate to skip entities that are already loaded in the current Persistence Context.
If the entities are not available in the current Persistence Context but they could be loaded from the second-level cache, you can use the
with(CacheMode)
method of the MultiIdentifierLoadAccess
object.
Example 362. Loading multiple entities from the second-level cache
SessionFactory sessionFactory = scope.getEntityManagerFactory().unwrap(SessionFactory.class);
Statistics statistics = sessionFactory.getStatistics();
sessionFactory.getCache().evictAll();
statistics.clear();
final SQLStatementInspector sqlStatementInspector = scope.getStatementInspector( SQLStatementInspector.class );
sqlStatementInspector.clear();
assertEquals(0, statistics.getQueryExecutionCount());
scope.inTransaction(
entityManager -> {
Session session = entityManager.unwrap(Session.class);
List<Person> persons = session
.byMultipleIds(Person.class)
.multiLoad(1L, 2L, 3L);
assertEquals(3, persons.size());
}
);
assertEquals(0, statistics.getSecondLevelCacheHitCount());
assertEquals(3, statistics.getSecondLevelCachePutCount());
assertEquals(1, sqlStatementInspector.getSqlQueries().size());
scope.inTransaction(
entityManager -> {
Session session = entityManager.unwrap(Session.class);
sqlStatementInspector.clear();
List<Person> persons = session.byMultipleIds(Person.class)
.with(CacheMode.NORMAL)
.multiLoad(1L, 2L, 3L);
assertEquals(3, persons.size());
}
);
assertEquals(3, statistics.getSecondLevelCacheHitCount());
assertEquals(0, sqlStatementInspector.getSqlQueries().size());
In the example above, we first make sure that we clear the second-level cache to demonstrate that
the multi-load query will put the returning entities into the second-level cache.
After executing the first byMultipleIds
call, Hibernate is going to fetch the requested entities,
and as illustrated by the getSecondLevelCachePutCount
method call, 3 entities were indeed added to the
shared cache.
Afterward, when executing the second byMultipleIds
call for the same entities in a new Hibernate Session
,
we set the
CacheMode.NORMAL
second-level cache mode so that entities are going to be returned from the second-level cache.
The getSecondLevelCacheHitCount
statistics method returns 3 this time, since the 3 entities were loaded from the second-level cache, and, as illustrated by sqlStatementInterceptor.getSqlQueries()
, no multi-load SELECT statement was executed this time.
5.8. Obtain an entity by natural-id
In addition to allowing to load the entity by its identifier, Hibernate allows applications to load entities by the declared natural identifier.
Example 363. Natural-id mapping
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
@NaturalId
private String isbn;
@ManyToOne
private Person author;
//Getters and setters are omitted for brevity
}
We can also opt to fetch the entity or just retrieve a reference to it when using the natural identifier loading methods.
Example 364. Get entity reference by simple natural-id
Book book = session.bySimpleNaturalId(Book.class).getReference(isbn);
Example 365. Load entity by natural-id
Book book = session
.byNaturalId(Book.class)
.using("isbn", isbn)
.load();
We can also use a Java 8 Optional
to load an entity by its natural id:
Example 366. Load an Optional entity by natural-id
Optional<Book> optionalBook = session
.byNaturalId(Book.class)
.using("isbn", isbn)
.loadOptional();
Hibernate offers a consistent API for accessing persistent data by identifier or by the natural-id. Each of these defines the same two data access methods:
- getReference
-
Should be used in cases where the identifier is assumed to exist, where non-existence would be an actual error.
Should never be used to test existence.
That is because this method will prefer to create and return a proxy if the data is not already associated with the Session rather than hit the database.
The quintessential use-case for using this method is to create foreign key based associations. - load
-
Will return the persistent data associated with the given identifier value or null if that identifier does not exist.
Each of these two methods defines an overloading variant accepting a org.hibernate.LockOptions
argument.
Locking is discussed in a separate chapter.
5.9. Filtering entities and associations
Hibernate offers two options if you want to filter entities or entity associations:
- static (e.g.
@SQLRestriction
and@SQLJoinTableRestriction
) -
which are defined at mapping time and
cannot change at runtime. - dynamic (e.g.
@Filter
and@FilterJoinTable
) -
which are applied and configured at runtime.
5.9.1. @SQLRestriction
Sometimes, you want to filter out entities or collections using custom SQL criteria.
This can be achieved using the @SQLRestriction
annotation, which can be applied to entities and collections.
Example 367. @SQLRestriction
mapping usage
public enum AccountType {
DEBIT,
CREDIT
}
@Entity(name = "Client")
public static class Client {
@Id
private Long id;
private String name;
@SQLRestriction("account_type = 'DEBIT'")
@OneToMany(mappedBy = "client")
private List<Account> debitAccounts = new ArrayList<>();
@SQLRestriction("account_type = 'CREDIT'")
@OneToMany(mappedBy = "client")
private List<Account> creditAccounts = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Account")
@SQLRestriction("active = true")
public static class Account {
@Id
private Long id;
@ManyToOne
private Client client;
@Column(name = "account_type")
@Enumerated(EnumType.STRING)
private AccountType type;
private Double amount;
private Double rate;
private boolean active;
//Getters and setters omitted for brevity
}
If the database contains the following entities:
Example 368. Persisting and fetching entities with a @SQLRestriction
mapping
doInJPA(this::entityManagerFactory, entityManager -> {
Client client = new Client();
client.setId(1L);
client.setName("John Doe");
entityManager.persist(client);
Account account1 = new Account();
account1.setId(1L);
account1.setType(AccountType.CREDIT);
account1.setAmount(5000d);
account1.setRate(1.25 / 100);
account1.setActive(true);
account1.setClient(client);
client.getCreditAccounts().add(account1);
entityManager.persist(account1);
Account account2 = new Account();
account2.setId(2L);
account2.setType(AccountType.DEBIT);
account2.setAmount(0d);
account2.setRate(1.05 / 100);
account2.setActive(false);
account2.setClient(client);
client.getDebitAccounts().add(account2);
entityManager.persist(account2);
Account account3 = new Account();
account3.setType(AccountType.DEBIT);
account3.setId(3L);
account3.setAmount(250d);
account3.setRate(1.05 / 100);
account3.setActive(true);
account3.setClient(client);
client.getDebitAccounts().add(account3);
entityManager.persist(account3);
});
INSERT INTO Client (name, id)
VALUES ('John Doe', 1)
INSERT INTO Account (active, amount, client_id, rate, account_type, id)
VALUES (true, 5000.0, 1, 0.0125, 'CREDIT', 1)
INSERT INTO Account (active, amount, client_id, rate, account_type, id)
VALUES (false, 0.0, 1, 0.0105, 'DEBIT', 2)
INSERT INTO Account (active, amount, client_id, rate, account_type, id)
VALUES (true, 250.0, 1, 0.0105, 'DEBIT', 3)
When executing an Account
entity query, Hibernate is going to filter out all records that are not active.
Example 369. Query entities mapped with @SQLRestriction
doInJPA(this::entityManagerFactory, entityManager -> {
List<Account> accounts = entityManager.createQuery(
"select a from Account a", Account.class)
.getResultList();
assertEquals(2, accounts.size());
});
SELECT
a.id as id1_0_,
a.active as active2_0_,
a.amount as amount3_0_,
a.client_id as client_i6_0_,
a.rate as rate4_0_,
a.account_type as account_5_0_
FROM
Account a
WHERE ( a.active = true )
When fetching the debitAccounts
or the creditAccounts
collections, Hibernate is going to apply the @SQLRestriction
clause filtering criteria to the associated child entities.
Example 370. Traversing collections mapped with @SQLRestriction
doInJPA(this::entityManagerFactory, entityManager -> {
Client client = entityManager.find(Client.class, 1L);
assertEquals(1, client.getCreditAccounts().size());
assertEquals(1, client.getDebitAccounts().size());
});
SELECT
c.client_id as client_i6_0_0_,
c.id as id1_0_0_,
c.id as id1_0_1_,
c.active as active2_0_1_,
c.amount as amount3_0_1_,
c.client_id as client_i6_0_1_,
c.rate as rate4_0_1_,
c.account_type as account_5_0_1_
FROM
Account c
WHERE ( c.active = true and c.account_type = 'CREDIT' ) AND c.client_id = 1
SELECT
d.client_id as client_i6_0_0_,
d.id as id1_0_0_,
d.id as id1_0_1_,
d.active as active2_0_1_,
d.amount as amount3_0_1_,
d.client_id as client_i6_0_1_,
d.rate as rate4_0_1_,
d.account_type as account_5_0_1_
FROM
Account d
WHERE ( d.active = true and d.account_type = 'DEBIT' ) AND d.client_id = 1
5.9.2. @SQLJoinTableRestriction
Just like @SQLRestriction
annotation, @SQLJoinTableRestriction
is used to filter out collections using a joined table (e.g. @ManyToMany association).
Example 371. @SQLJoinTableRestriction
mapping example
@Entity(name = "Book")
public static class Book {
@Id
private Long id;
private String title;
private String author;
@ManyToMany
@JoinTable(
name = "Book_Reader",
joinColumns = @JoinColumn(name = "book_id"),
inverseJoinColumns = @JoinColumn(name = "reader_id")
)
@SQLJoinTableRestriction("created_on > DATEADD('DAY', -7, CURRENT_TIMESTAMP())")
private List<Reader> currentWeekReaders = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Reader")
public static class Reader {
@Id
private Long id;
private String name;
//Getters and setters omitted for brevity
}
create table Book (
id bigint not null,
author varchar(255),
title varchar(255),
primary key (id)
)
create table Book_Reader (
book_id bigint not null,
reader_id bigint not null
)
create table Reader (
id bigint not null,
name varchar(255),
primary key (id)
)
alter table Book_Reader
add constraint FKsscixgaa5f8lphs9bjdtpf9g
foreign key (reader_id)
references Reader
alter table Book_Reader
add constraint FKoyrwu9tnwlukd1616qhck21ra
foreign key (book_id)
references Book
alter table Book_Reader
add created_on timestamp
default current_timestamp
In the example above, the current week Reader
entities are included in the currentWeekReaders
collection
which uses the @SQLJoinTableRestriction
annotation to filter the joined table rows according to the provided SQL clause.
Considering that the following two Book_Reader
entries are added into our system:
Example 372. @SQLJoinTableRestriction
test data
Book book = new Book();
book.setId(1L);
book.setTitle("High-Performance Java Persistence");
book.setAuthor("Vad Mihalcea");
entityManager.persist(book);
Reader reader1 = new Reader();
reader1.setId(1L);
reader1.setName("John Doe");
entityManager.persist(reader1);
Reader reader2 = new Reader();
reader2.setId(2L);
reader2.setName("John Doe Jr.");
entityManager.persist(reader2);
statement.executeUpdate(
"INSERT INTO Book_Reader " +
" (book_id, reader_id) " +
"VALUES " +
" (1, 1) "
);
statement.executeUpdate(
"INSERT INTO Book_Reader " +
" (book_id, reader_id, created_on) " +
"VALUES " +
" (1, 2, DATEADD('DAY', -10, CURRENT_TIMESTAMP())) "
);
When fetching the currentWeekReaders
collection, Hibernate is going to find only one entry:
Example 373. @SQLJoinTableRestriction
fetch example
Book book = entityManager.find(Book.class, 1L);
assertEquals(1, book.getCurrentWeekReaders().size());
5.9.3. @Filter
The @Filter
annotation is another way to filter out entities or collections using custom SQL criteria.
Unlike the @SQLRestriction
annotation, @Filter
allows you to parameterize the filter clause at runtime.
Now, considering we have the following Account
entity:
Example 374. @Filter
mapping entity-level usage
@Entity(name = "Account")
@Table(name = "account")
@FilterDef(
name="activeAccount",
parameters = @ParamDef(
name="active",
type=Boolean.class
)
)
@Filter(
name="activeAccount",
condition="active_status = :active"
)
public static class Account {
@Id
private Long id;
@ManyToOne(fetch = FetchType.LAZY)
private Client client;
@Column(name = "account_type")
@Enumerated(EnumType.STRING)
private AccountType type;
private Double amount;
private Double rate;
@Column(name = "active_status")
private boolean active;
//Getters and setters omitted for brevity
}
Notice that the This mapping was done to show you that the |
As already explained, we can also apply the @Filter
annotation for collections as illustrated by the Client
entity:
Example 375. @Filter
mapping collection-level usage
@Entity(name = "Client")
@Table(name = "client")
public static class Client {
@Id
private Long id;
private String name;
private AccountType type;
@OneToMany(
mappedBy = "client",
cascade = CascadeType.ALL
)
@Filter(
name="activeAccount",
condition="active_status = :active"
)
private List<Account> accounts = new ArrayList<>();
//Getters and setters omitted for brevity
public void addAccount(Account account) {
account.setClient(this);
this.accounts.add(account);
}
}
If we persist a Client
with three associated Account
entities,
Hibernate will execute the following SQL statements:
Example 376. Persisting and fetching entities with a @Filter
mapping
Client client = new Client()
.setId(1L)
.setName("John Doe")
.setType(AccountType.DEBIT);
client.addAccount(
new Account()
.setId(1L)
.setType(AccountType.CREDIT)
.setAmount(5000d)
.setRate(1.25 / 100)
.setActive(true)
);
client.addAccount(
new Account()
.setId(2L)
.setType(AccountType.DEBIT)
.setAmount(0d)
.setRate(1.05 / 100)
.setActive(false)
);
client.addAccount(
new Account()
.setType(AccountType.DEBIT)
.setId(3L)
.setAmount(250d)
.setRate(1.05 / 100)
.setActive(true)
);
entityManager.persist(client);
INSERT INTO Client (name, id)
VALUES ('John Doe', 1)
INSERT INTO Account (active_status, amount, client_id, rate, account_type, id)
VALUES (true, 5000.0, 1, 0.0125, 'CREDIT', 1)
INSERT INTO Account (active_status, amount, client_id, rate, account_type, id)
VALUES (false, 0.0, 1, 0.0105, 'DEBIT', 2)
INSERT INTO Account (active_status, amount, client_id, rate, account_type, id)
VALUES (true, 250.0, 1, 0.0105, 'DEBIT', 3)
By default, without explicitly enabling the filter, Hibernate is going to fetch all Account
entities.
Example 377. Query entities mapped without activating the @Filter
List<Account> accounts = entityManager.createQuery(
"select a from Account a", Account.class)
.getResultList();
assertEquals(3, accounts.size());
SELECT
a.id as id1_0_,
a.active_status as active2_0_,
a.amount as amount3_0_,
a.client_id as client_i6_0_,
a.rate as rate4_0_,
a.account_type as account_5_0_
FROM
Account a
If the filter is enabled and the filter parameter value is provided,
then Hibernate is going to apply the filtering criteria to the associated Account
entities.
Example 378. Query entities mapped with @Filter
entityManager
.unwrap(Session.class)
.enableFilter("activeAccount")
.setParameter("active", true);
List<Account> accounts = entityManager.createQuery(
"select a from Account a", Account.class)
.getResultList();
assertEquals(2, accounts.size());
SELECT
a.id as id1_0_,
a.active_status as active2_0_,
a.amount as amount3_0_,
a.client_id as client_i6_0_,
a.rate as rate4_0_,
a.account_type as account_5_0_
FROM
Account a
WHERE
a.active_status = true
Filters apply to entity queries, but not to direct fetching. Therefore, in the following example, the filter is not taken into consideration when fetching an entity from the Persistence Context. Fetching entities mapped with
As you can see from the example above, contrary to an entity query, the filter does not prevent the entity from being loaded. |
Just like with entity queries, collections can be filtered as well, but only if the filter is explicitly enabled on the currently running Hibernate Session
.
Example 379. Traversing collections without activating the @Filter
Client client = entityManager.find(Client.class, 1L);
assertEquals(3, client.getAccounts().size());
SELECT
c.id as id1_1_0_,
c.name as name2_1_0_
FROM
Client c
WHERE
c.id = 1
SELECT
a.id as id1_0_,
a.active_status as active2_0_,
a.amount as amount3_0_,
a.client_id as client_i6_0_,
a.rate as rate4_0_,
a.account_type as account_5_0_
FROM
Account a
WHERE
a.client_id = 1
When activating the @Filter
and fetching the accounts
collections, Hibernate is going to apply the filter condition to the associated collection entries.
Example 380. Traversing collections mapped with @Filter
entityManager
.unwrap(Session.class)
.enableFilter("activeAccount")
.setParameter("active", true);
Client client = entityManager.find(Client.class, 1L);
assertEquals(2, client.getAccounts().size());
SELECT
c.id as id1_1_0_,
c.name as name2_1_0_
FROM
Client c
WHERE
c.id = 1
SELECT
a.id as id1_0_,
a.active_status as active2_0_,
a.amount as amount3_0_,
a.client_id as client_i6_0_,
a.rate as rate4_0_,
a.account_type as account_5_0_
FROM
Account a
WHERE
accounts0_.active_status = true
and a.client_id = 1
The main advantage of |
It’s not possible to combine the If caching were allowed for a currently filtered collection, then the second-level cache would store only a subset of the whole collection. For this reason, the second-level collection cache is limited to storing whole collections, and not subsets. |
5.9.4. @Filter
with @SqlFragmentAlias
When using the @Filter
annotation and working with entities that are mapped onto multiple database tables,
you will need to use the
@SqlFragmentAlias
annotation
if the @Filter
defines a condition that uses predicates across multiple tables.
Example 381. @SqlFragmentAlias
mapping usage
@Entity(name = "Account")
@Table(name = "account")
@Comment(on="account", value = "The account table")
@SecondaryTable(
name = "account_details"
)
@Comment(on="account_details", value = "The account details secondary table")
@SQLDelete(
sql = "UPDATE account_details SET deleted = true WHERE id = ? "
)
@FilterDef(
name="activeAccount",
parameters = @ParamDef(
name="active",
type=Boolean.class
)
)
@Filter(
name="activeAccount",
condition="{a}.active = :active and {ad}.deleted = false",
aliases = {
@SqlFragmentAlias(alias = "a", table= "account"),
@SqlFragmentAlias(alias = "ad", table= "account_details"),
}
)
public static class Account {
@Id
private Long id;
private Double amount;
private Double rate;
private boolean active;
@Column(table = "account_details")
private boolean deleted;
//Getters and setters omitted for brevity
}
Now, when fetching the Account
entities and activating the filter,
Hibernate is going to apply the right table aliases to the filter predicates:
Example 382. Fetching a collection filtered with @SqlFragmentAlias
entityManager
.unwrap(Session.class)
.enableFilter("activeAccount")
.setParameter("active", true);
List<Account> accounts = entityManager.createQuery(
"select a from Account a", Account.class)
.getResultList();
select
filtersqlf0_.id as id1_0_,
filtersqlf0_.active as active2_0_,
filtersqlf0_.amount as amount3_0_,
filtersqlf0_.rate as rate4_0_,
filtersqlf0_1_.deleted as deleted1_1_
from
account filtersqlf0_
left outer join
account_details filtersqlf0_1_
on filtersqlf0_.id=filtersqlf0_1_.id
where
filtersqlf0_.active = ?
and filtersqlf0_1_.deleted = false
-- binding parameter [1] as [BOOLEAN] - [true]
5.9.5. @FilterJoinTable
When using the @Filter
annotation with collections, the filtering is done against the child entries (entities or embeddables).
However, if you have a link table between the parent entity and the child table, then you need to use the @FilterJoinTable
to filter child entries according to some column contained in the join table.
The @FilterJoinTable
annotation can be, therefore, applied to a unidirectional @OneToMany
collection as illustrated in the following mapping:
Example 383. @FilterJoinTable
mapping usage
@Entity(name = "Client")
@FilterDef(
name="firstAccounts",
parameters=@ParamDef(
name="maxOrderId",
type=int.class
)
)
public static class Client {
@Id
private Long id;
private String name;
@OneToMany(cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
@FilterJoinTable(
name="firstAccounts",
condition="order_id <= :maxOrderId"
)
private List<Account> accounts = new ArrayList<>();
//Getters and setters omitted for brevity
public void addAccount(Account account) {
this.accounts.add(account);
}
}
@Entity(name = "Account")
public static class Account {
@Id
private Long id;
@Column(name = "account_type")
@Enumerated(EnumType.STRING)
private AccountType type;
private Double amount;
private Double rate;
//Getters and setters omitted for brevity
}
The firstAccounts
filter will allow us to get only the Account
entities that have the order_id
(which tells the position of every entry inside the accounts
collection)
less than a given number (e.g. maxOrderId
).
Let’s assume our database contains the following entities:
Example 384. Persisting and fetching entities with a @FilterJoinTable
mapping
Client client = new Client()
.setId(1L)
.setName("John Doe");
client.addAccount(
new Account()
.setId(1L)
.setType(AccountType.CREDIT)
.setAmount(5000d)
.setRate(1.25 / 100)
);
client.addAccount(
new Account()
.setId(2L)
.setType(AccountType.DEBIT)
.setAmount(0d)
.setRate(1.05 / 100)
);
client.addAccount(
new Account()
.setType(AccountType.DEBIT)
.setId(3L)
.setAmount(250d)
.setRate(1.05 / 100)
);
entityManager.persist(client);
INSERT INTO Client (name, id)
VALUES ('John Doe', 1)
INSERT INTO Account (amount, client_id, rate, account_type, id)
VALUES (5000.0, 1, 0.0125, 'CREDIT', 1)
INSERT INTO Account (amount, client_id, rate, account_type, id)
VALUES (0.0, 1, 0.0105, 'DEBIT', 2)
INSERT INTO Account (amount, client_id, rate, account_type, id)
VALUES (250.0, 1, 0.0105, 'DEBIT', 3)
INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 0, 1)
INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 0, 1)
INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 1, 2)
INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 2, 3)
The collections can be filtered only if the associated filter is enabled on the currently running Hibernate Session
.
Example 385. Traversing collections mapped with @FilterJoinTable
without enabling the filter
Client client = entityManager.find(Client.class, 1L);
assertEquals(3, client.getAccounts().size());
SELECT
ca.Client_id as Client_i1_2_0_,
ca.accounts_id as accounts2_2_0_,
ca.order_id as order_id3_0_,
a.id as id1_0_1_,
a.amount as amount3_0_1_,
a.rate as rate4_0_1_,
a.account_type as account_5_0_1_
FROM
Client_Account ca
INNER JOIN
Account a
ON ca.accounts_id=a.id
WHERE
ca.Client_id = ?
-- binding parameter [1] as [BIGINT] - [1]
If we enable the filter and set the maxOrderId
to 1
when fetching the accounts
collections, Hibernate is going to apply the @FilterJoinTable
clause filtering criteria, and we will get just
2
Account
entities, with the order_id
values of 0
and 1
.
Example 386. Traversing collections mapped with @FilterJoinTable
Client client = entityManager.find(Client.class, 1L);
entityManager
.unwrap(Session.class)
.enableFilter("firstAccounts")
.setParameter("maxOrderId", 1);
assertEquals(2, client.getAccounts().size());
SELECT
ca.Client_id as Client_i1_2_0_,
ca.accounts_id as accounts2_2_0_,
ca.order_id as order_id3_0_,
a.id as id1_0_1_,
a.amount as amount3_0_1_,
a.rate as rate4_0_1_,
a.account_type as account_5_0_1_
FROM
Client_Account ca
INNER JOIN
Account a
ON ca.accounts_id=a.id
WHERE
ca.order_id <= ?
AND ca.Client_id = ?
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [BIGINT] - [1]
5.10. Modifying managed/persistent state
Entities in managed/persistent state may be manipulated by the application, and any changes will be automatically detected and persisted when the persistence context is flushed.
There is no need to call a particular method to make your modifications persistent.
Example 387. Modifying managed state with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
person.setName("John Doe");
entityManager.flush();
Example 388. Modifying managed state with Hibernate API
Person person = session.byId(Person.class).load(personId);
person.setName("John Doe");
session.flush();
By default, when you modify an entity, all columns but the identifier are being set during update.
Therefore, considering you have the following Product
entity mapping:
Example 389. Product
entity mapping
@Entity(name = "Product")
public static class Product {
@Id
private Long id;
@Column
private String name;
@Column
private String description;
@Column(name = "price_cents")
private Integer priceCents;
@Column
private Integer quantity;
//Getters and setters are omitted for brevity
}
If you persist the following Product
entity:
Example 390. Persisting a Product
entity
Product book = new Product();
book.setId(1L);
book.setName("High-Performance Java Persistence");
book.setDescription("Get the most out of your persistence layer");
book.setPriceCents(29_99);
book.setQuantity(10_000);
entityManager.persist(book);
When you modify the Product
entity, Hibernate generates the following SQL UPDATE statement:
Example 391. Modifying the Product
entity
doInJPA(this::entityManagerFactory, entityManager -> {
Product book = entityManager.find(Product.class, 1L);
book.setPriceCents(24_99);
});
UPDATE
Product
SET
description = ?,
name = ?,
price_cents = ?,
quantity = ?
WHERE
id = ?
-- binding parameter [1] as [VARCHAR] - [Get the most out of your persistence layer]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [INTEGER] - [2499]
-- binding parameter [4] as [INTEGER] - [10000]
-- binding parameter [5] as [BIGINT] - [1]
The default UPDATE statement containing all columns has two advantages:
-
it allows you to better benefit from JDBC Statement caching.
-
it allows you to enable batch updates even if multiple entities modify different properties.
However, there is also one downside to including all columns in the SQL UPDATE statement.
If you have multiple indexes, the database might update those redundantly even if you don’t actually modify all column values.
To fix this issue, you can use dynamic updates.
5.10.1. Dynamic updates
To enable dynamic updates, you need to annotate the entity with the @DynamicUpdate
annotation:
Example 392. Product
entity mapping
@Entity(name = "Product")
@DynamicUpdate
public static class Product {
@Id
private Long id;
@Column
private String name;
@Column
private String description;
@Column(name = "price_cents")
private Integer priceCents;
@Column
private Integer quantity;
//Getters and setters are omitted for brevity
}
This time, when rerunning the previous test case, Hibernate generates the following SQL UPDATE statement:
Example 393. Modifying the Product
entity with a dynamic update
UPDATE
Product
SET
price_cents = ?
WHERE
id = ?
-- binding parameter [1] as [INTEGER] - [2499]
-- binding parameter [2] as [BIGINT] - [1]
The dynamic update allows you to set just the columns that were modified in the associated entity.
5.11. Refresh entity state
You can reload an entity instance and its collections at any time.
Example 394. Refreshing entity state with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
entityManager.createQuery("update Person set name = UPPER(name)").executeUpdate();
entityManager.refresh(person);
assertEquals("JOHN DOE", person.getName());
Example 395. Refreshing entity state with Hibernate API
Person person = session.byId(Person.class).load(personId);
session.doWork(connection -> {
try(Statement statement = connection.createStatement()) {
statement.executeUpdate("UPDATE Person SET name = UPPER(name)");
}
});
session.refresh(person);
assertEquals("JOHN DOE", person.getName());
One case where this is useful is when it is known that the database state has changed since the data was read.
Refreshing allows the current database state to be pulled into the entity instance and the persistence context.
Another case where this might be useful is when database triggers are used to initialize some of the properties of the entity.
Only the entity instance and its value type collections are refreshed unless you specify |
Traditionally, Hibernate allowed detached entities to be refreshed. For this reason, when bootstrapping the Hibernate However, this default behavior can be overwritten through the For more about the |
5.11.1. Refresh gotchas
The refresh
entity state transition is meant to overwrite the entity attributes according to the info currently contained in the associated database record.
However, you have to be very careful when cascading the refresh action to any transient entity.
For instance, consider the following example:
Example 396. Refreshing entity state gotcha
try {
Person person = entityManager.find(Person.class, personId);
Book book = new Book();
book.setId(100L);
book.setTitle("Hibernate User Guide");
book.setAuthor(person);
person.getBooks().add(book);
entityManager.refresh(person);
}
catch (EntityNotFoundException expected) {
log.info("Beware when cascading the refresh associations to transient entities!");
}
In the aforementioned example, an EntityNotFoundException
is thrown because the Book
entity is still in a transient state.
When the refresh action is cascaded from the Person
entity, Hibernate will not be able to locate the Book
entity in the database.
For this reason, you should be very careful when mixing the refresh action with transient child entity objects.
5.12. Working with detached data
Detachment is the process of working with data outside the scope of any persistence context.
Data becomes detached in a number of ways.
Once the persistence context is closed, all data that was associated with it becomes detached.
Clearing the persistence context has the same effect.
Evicting a particular entity from the persistence context makes it detached.
And finally, serialization will make the deserialized form be detached (the original instance is still managed).
Detached data can still be manipulated, however, the persistence context will no longer automatically know about these modifications, and the application will need to intervene to make the changes persistent again.
5.12.1. Reattaching detached data
Reattachment is the process of taking an incoming entity instance that is in the detached state and re-associating it with the current persistence context.
Jakarta Persistence does not support reattaching detached data. This is only available through Hibernate |
Example 397. Reattaching a detached entity using lock
Person person = session.byId(Person.class).load(personId);
//Clear the Session so the person entity becomes detached
session.clear();
person.setName("Mr. John Doe");
session.lock(person, LockMode.NONE);
Example 398. Reattaching a detached entity using saveOrUpdate
Person person = session.byId(Person.class).load(personId);
//Clear the Session so the person entity becomes detached
session.clear();
person.setName("Mr. John Doe");
session.merge(person);
The method name |
Provided the entity is detached, update
and saveOrUpdate
operate exactly the same.
5.12.2. Merging detached data
Merging is the process of taking an incoming entity instance that is in the detached state and copying its data over onto a new managed instance.
Although not exactly per se, the following example is a good visualization of the merge
operation internals.
Example 399. Visualizing merge
public Person merge(Person detached) {
Person newReference = session.byId(Person.class).load(detached.getId());
newReference.setName(detached.getName());
return newReference;
}
Example 400. Merging a detached entity with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
//Clear the EntityManager so the person entity becomes detached
entityManager.clear();
person.setName("Mr. John Doe");
person = entityManager.merge(person);
Example 401. Merging a detached entity with Hibernate API
Person person = session.byId(Person.class).load(personId);
//Clear the Session so the person entity becomes detached
session.clear();
person.setName("Mr. John Doe");
person = (Person) session.merge(person);
Merging gotchas
For example, Hibernate throws IllegalStateException
when merging a parent entity which has references to 2 detached child entities child1
and child2
(obtained from different sessions), and child1
and child2
represent the same persistent entity, Child
.
A new configuration property, hibernate.event.merge.entity_copy_observer
, controls how Hibernate will respond when multiple representations of the same persistent entity («entity copy») is detected while merging.
The possible values are:
- disallow (the default)
-
throws
IllegalStateException
if an entity copy is detected - allow
-
performs the merge operation on each entity copy that is detected
- log
-
(provided for testing only) performs the merge operation on each entity copy that is detected and logs information about the entity copies.
This setting requires DEBUG logging be enabled fororg.hibernate.event.internal.EntityCopyAllowedLoggedObserver
In addition, the application may customize the behavior by providing an implementation of org.hibernate.event.spi.EntityCopyObserver
and setting hibernate.event.merge.entity_copy_observer
to the class name.
When this property is set to allow
or log
, Hibernate will merge each entity copy detected while cascading the merge operation.
In the process of merging each entity copy, Hibernate will cascade the merge operation from each entity copy to its associations with cascade=CascadeType.MERGE
or CascadeType.ALL
.
The entity state resulting from merging an entity copy will be overwritten when another entity copy is merged.
Because cascade order is undefined, the order in which the entity copies are merged is undefined. If an entity copy cascades the merge operation to an association that is (or contains) a new entity, that new entity will be merged (i.e., persisted and the merge operation will be cascaded to its associations according to its mapping), If the association is mapped with There are known issues when representations of the same persistent entity have different values for a collection. By setting The only way to exclude particular entity classes or associations that contain critical data is to provide a custom implementation of |
Hibernate provides limited DEBUG logging capabilities that can help determine the entity classes for which entity copies were found.
The log should be reviewed to determine if multiple representations of entities containing critical data are detected. Using optimistic locking is recommended to detect if different representations are from different versions of the same persistent entity. |
5.13. Checking persistent state
An application can verify the state of entities and collections in relation to the persistence context.
Example 402. Verifying managed state with Jakarta Persistence
boolean contained = entityManager.contains(person);
Example 403. Verifying managed state with Hibernate API
boolean contained = session.contains(person);
Example 404. Verifying laziness with Jakarta Persistence
PersistenceUnitUtil persistenceUnitUtil = entityManager.getEntityManagerFactory().getPersistenceUnitUtil();
boolean personInitialized = persistenceUnitUtil.isLoaded(person);
boolean personBooksInitialized = persistenceUnitUtil.isLoaded(person.getBooks());
boolean personNameInitialized = persistenceUnitUtil.isLoaded(person, "name");
Example 405. Verifying laziness with Hibernate API
boolean personInitialized = Hibernate.isInitialized(person);
boolean personBooksInitialized = Hibernate.isInitialized(person.getBooks());
boolean personNameInitialized = Hibernate.isPropertyInitialized(person, "name");
In Jakarta Persistence there is an alternative means to check laziness using the following jakarta.persistence.PersistenceUtil
pattern (which is recommended wherever possible).
Example 406. Alternative Jakarta Persistence means to verify laziness
PersistenceUtil persistenceUnitUtil = Persistence.getPersistenceUtil();
boolean personInitialized = persistenceUnitUtil.isLoaded(person);
boolean personBooksInitialized = persistenceUnitUtil.isLoaded(person.getBooks());
boolean personNameInitialized = persistenceUnitUtil.isLoaded(person, "name");
5.14. Evicting entities
When the flush()
method is called, the state of the entity is synchronized with the database.
If you do not want this synchronization to occur, or if you are processing a huge number of objects and need to manage memory efficiently,
the evict()
method can be used to remove the object and its collections from the first-level cache.
Example 407. Detaching an entity from the EntityManager
for(Person person : entityManager.createQuery("select p from Person p", Person.class)
.getResultList()) {
dtos.add(toDTO(person));
entityManager.detach(person);
}
Example 408. Evicting an entity from the Hibernate Session
Session session = entityManager.unwrap(Session.class);
for(Person person : (List<Person>) session.createSelectionQuery("select p from Person p").list()) {
dtos.add(toDTO(person));
session.evict(person);
}
To detach all entities from the current persistence context, both the EntityManager
and the Hibernate Session
define a clear()
method.
Example 409. Clearing the persistence context
entityManager.clear();
session.clear();
To verify if an entity instance is currently attached to the running persistence context, both the EntityManager
and the Hibernate Session
define a contains(Object entity)
method.
Example 410. Verify if an entity is contained in a persistence context
entityManager.contains(person);
session.contains(person);
5.15. Cascading entity state transitions
Jakarta Persistence allows you to propagate the state transition from a parent entity to a child.
For this purpose, the Jakarta Persistence jakarta.persistence.CascadeType
defines various cascade types:
ALL
-
cascades all entity state transitions.
PERSIST
-
cascades the entity persist operation.
MERGE
-
cascades the entity merge operation.
REMOVE
-
cascades the entity remove operation.
REFRESH
-
cascades the entity refresh operation.
DETACH
-
cascades the entity detach operation.
Additionally, the CascadeType.ALL
will propagate any Hibernate-specific operation, which is defined by the org.hibernate.annotations.CascadeType
enum:
SAVE_UPDATE
-
cascades the entity saveOrUpdate operation.
REPLICATE
-
cascades the entity replicate operation.
LOCK
-
cascades the entity lock operation.
The following examples will explain some of the aforementioned cascade operations using the following entities:
@Entity
public class Person {
@Id
private Long id;
private String name;
@OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
public void addPhone(Phone phone) {
this.phones.add(phone);
phone.setOwner(this);
}
}
@Entity
public class Phone {
@Id
private Long id;
@Column(name = "`number`")
private String number;
@ManyToOne(fetch = FetchType.LAZY)
private Person owner;
//Getters and setters are omitted for brevity
}
5.15.1. CascadeType.PERSIST
The CascadeType.PERSIST
allows us to persist a child entity along with the parent one.
Example 411. CascadeType.PERSIST
example
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("123-456-7890");
person.addPhone(phone);
entityManager.persist(person);
INSERT INTO Person ( name, id )
VALUES ( 'John Doe', 1 )
INSERT INTO Phone ( `number`, person_id, id )
VALUE ( '123-456-7890', 1, 1 )
Even if just the Person
parent entity was persisted, Hibernate has managed to cascade the persist operation to the associated Phone
child entity as well.
5.15.2. CascadeType.MERGE
The CascadeType.MERGE
allows us to merge a child entity along with the parent one.
Example 412. CascadeType.MERGE
example
Phone phone = entityManager.find(Phone.class, 1L);
Person person = phone.getOwner();
person.setName("John Doe Jr.");
phone.setNumber("987-654-3210");
entityManager.clear();
entityManager.merge(person);
SELECT
p.id as id1_0_1_,
p.name as name2_0_1_,
ph.owner_id as owner_id3_1_3_,
ph.id as id1_1_3_,
ph.id as id1_1_0_,
ph."number" as number2_1_0_,
ph.owner_id as owner_id3_1_0_
FROM
Person p
LEFT OUTER JOIN
Phone ph
on p.id=ph.owner_id
WHERE
p.id = 1
During merge, the current state of the entity is copied onto the entity version that was just fetched from the database.
That’s the reason why Hibernate executed the SELECT statement which fetched both the Person
entity along with its children.
5.15.3. CascadeType.REMOVE
The CascadeType.REMOVE
allows us to remove a child entity along with the parent one.
Traditionally, Hibernate called this operation delete, that’s why the org.hibernate.annotations.CascadeType
provides a DELETE
cascade option.
However, CascadeType.REMOVE
and org.hibernate.annotations.CascadeType.DELETE
are identical.
Example 413. CascadeType.REMOVE
example
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);
DELETE FROM Phone WHERE id = 1
DELETE FROM Person WHERE id = 1
5.15.4. CascadeType.DETACH
CascadeType.DETACH
is used to propagate the detach operation from a parent entity to a child.
Example 414. CascadeType.DETACH
example
Person person = entityManager.find(Person.class, 1L);
assertEquals(1, person.getPhones().size());
Phone phone = person.getPhones().get(0);
assertTrue(entityManager.contains(person));
assertTrue(entityManager.contains(phone));
entityManager.detach(person);
assertFalse(entityManager.contains(person));
assertFalse(entityManager.contains(phone));
5.15.5. CascadeType.LOCK
Although unintuitively, CascadeType.LOCK
does not propagate a lock request from a parent entity to its children.
Such a use case requires the use of the PessimisticLockScope.EXTENDED
value of the jakarta.persistence.lock.scope
property.
However, CascadeType.LOCK
allows us to reattach a parent entity along with its children to the currently running Persistence Context.
Example 415. CascadeType.LOCK
example
Person person = entityManager.find(Person.class, 1L);
assertEquals(1, person.getPhones().size());
Phone phone = person.getPhones().get(0);
assertTrue(entityManager.contains(person));
assertTrue(entityManager.contains(phone));
entityManager.detach(person);
assertFalse(entityManager.contains(person));
assertFalse(entityManager.contains(phone));
entityManager.unwrap(Session.class)
.lock(person, new LockOptions(LockMode.NONE));
assertTrue(entityManager.contains(person));
assertTrue(entityManager.contains(phone));
5.15.6. CascadeType.REFRESH
The CascadeType.REFRESH
is used to propagate the refresh operation from a parent entity to a child.
The refresh operation will discard the current entity state, and it will override it using the one loaded from the database.
Example 416. CascadeType.REFRESH
example
Person person = entityManager.find(Person.class, 1L);
Phone phone = person.getPhones().get(0);
person.setName("John Doe Jr.");
phone.setNumber("987-654-3210");
entityManager.refresh(person);
assertEquals("John Doe", person.getName());
assertEquals("123-456-7890", phone.getNumber());
SELECT
p.id as id1_0_1_,
p.name as name2_0_1_,
ph.owner_id as owner_id3_1_3_,
ph.id as id1_1_3_,
ph.id as id1_1_0_,
ph."number" as number2_1_0_,
ph.owner_id as owner_id3_1_0_
FROM
Person p
LEFT OUTER JOIN
Phone ph
ON p.id=ph.owner_id
WHERE
p.id = 1
In the aforementioned example, you can see that both the Person
and Phone
entities are refreshed even if we only called this operation on the parent entity only.
5.15.7. CascadeType.REPLICATE
The CascadeType.REPLICATE
is to replicate both the parent and the child entities.
The replicate operation allows you to synchronize entities coming from different sources of data.
Example 417. CascadeType.REPLICATE
example
Person person = new Person();
person.setId(1L);
person.setName("John Doe Sr.");
Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("(01) 123-456-7890");
person.addPhone(phone);
entityManager.unwrap(Session.class).replicate(person, ReplicationMode.OVERWRITE);
SELECT
id
FROM
Person
WHERE
id = 1
SELECT
id
FROM
Phone
WHERE
id = 1
UPDATE
Person
SET
name = 'John Doe Sr.'
WHERE
id = 1
UPDATE
Phone
SET
"number" = '(01) 123-456-7890',
owner_id = 1
WHERE
id = 1
As illustrated by the SQL statements being generated, both the Person
and Phone
entities are replicated to the underlying database rows.
5.15.8. @OnDelete
cascade
While the previous cascade types propagate entity state transitions, the @OnDelete
cascade is a DDL-level FK feature which allows you
to remove a child record whenever the parent row is deleted.
So, when annotating the @ManyToOne
association with @OnDelete( action = OnDeleteAction.CASCADE )
,
the automatic schema generator will apply the ON DELETE CASCADE SQL directive to the Foreign Key declaration,
as illustrated by the following example.
Example 418. @OnDelete
@ManyToOne
mapping
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
@Column(name = "`number`")
private String number;
@ManyToOne(fetch = LAZY)
@OnDelete(action = CASCADE)
private Person owner;
//Getters and setters are omitted for brevity
}
create table Person (
id bigint not null,
name varchar(255),
primary key (id)
)
create table Phone (
id bigint not null,
"number" varchar(255),
owner_id bigint,
primary key (id)
)
alter table Phone
add constraint FK82m836qc1ss2niru7eogfndhl
foreign key (owner_id)
references Person
on delete cascade
Now, you can just remove the Person
entity, and the associated Phone
entities are going to be deleted automatically via the Foreign Key cascade.
Example 419. @OnDelete
@ManyToOne
delete example
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);
delete from Person where id = ?
-- binding parameter [1] as [BIGINT] - [1]
The @OnDelete
annotation can also be placed on a collection, as
illustrated in the following example.
Example 420. @OnDelete
@OneToMany
mapping
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String name;
@OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
@OnDelete(action = OnDeleteAction.CASCADE)
private List<Phone> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
@Column(name = "`number`")
private String number;
@ManyToOne(fetch = FetchType.LAZY)
private Person owner;
//Getters and setters are omitted for brevity
}
Now, when removing the Person
entity, all the associated Phone
child entities are deleted via the Foreign Key cascade even if the @OneToMany
collection was using the CascadeType.ALL
attribute.
Example 421. @OnDelete
@ManyToOne
delete example
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);
delete from Person where id = ?
-- binding parameter [1] as [BIGINT] - [1]
Without the This way, only the parent entity gets deleted, and all the associated child records are removed by the database engine, instead of being deleted explicitly via |
5.16. Exception handling
If the Jakarta Persistence EntityManager
or the Hibernate-specific Session
throws an exception, including any JDBC SQLException
, you have to immediately rollback the database transaction and close the current EntityManager
or Session
.
Certain methods of the Jakarta Persistence EntityManager
or the Hibernate Session
will not leave the Persistence Context in a consistent state. As a rule of thumb, no exception thrown by Hibernate can be treated as recoverable. Ensure that the Session will be closed by calling the close()
method in a finally block.
Rolling back the database transaction does not put your business objects back into the state they were at the start of the transaction. This means that the database state and the business objects will be out of sync. Usually, this is not a problem because exceptions are not recoverable and you will have to start over after rollback anyway.
Both the PersistenceException
and the HibernateException
are runtime exceptions because, in our opinion, we should not force the application developer to catch an unrecoverable exception at a low layer. In most systems, unchecked and fatal exceptions are handled in one of the first frames of the method call stack (i.e., in higher layers) and either an error message is presented to the application user or some other appropriate action is taken. Note that Hibernate might also throw other unchecked exceptions that are not a HibernateException
. These are not recoverable either, and appropriate action should be taken.
Hibernate wraps the JDBC SQLException
, thrown while interacting with the database, in a
JDBCException
.
In fact, Hibernate will attempt to convert the exception into a more meaningful subclass of JDBCException
. The underlying SQLException
is always available via JDBCException.getSQLException()
. Hibernate converts the SQLException
into an appropriate JDBCException subclass using the
SQLExceptionConverter
attached to the current SessionFactory
.
By default, the SQLExceptionConverter
is defined by the configured Hibernate Dialect
via the
buildSQLExceptionConversionDelegate
method
which is overridden by several database-specific Dialect
s.
The standard JDBCException
subtypes are:
- ConstraintViolationException
-
indicates some form of integrity constraint violation.
- DataException
-
indicates that evaluation of the valid SQL statement against the given data
resulted in some illegal operation, mismatched types, truncation or incorrect cardinality. - GenericJDBCException
-
a generic exception which did not fall into any of the other categories.
- JDBCConnectionException
-
indicates an error with the underlying JDBC communication.
- LockAcquisitionException
-
indicates an error acquiring a lock level necessary to perform the requested operation.
- LockTimeoutException
-
indicates that the lock acquisition request has timed out.
- PessimisticLockException
-
indicates that a lock acquisition request has failed.
- QueryTimeoutException
-
indicates that the current executing query has timed out.
- SQLGrammarException
-
indicates a grammar or syntax problem with the issued SQL.
Starting with Hibernate 5.2, the Hibernate If your |
6. Flushing
Flushing is the process of synchronizing the state of the persistence context with the underlying database.
The EntityManager
and the Hibernate Session
expose a set of methods, through which the application developer can change the persistent state of an entity.
The persistence context acts as a transactional write-behind cache, queuing any entity state change.
Like any write-behind cache, changes are first applied in-memory and synchronized with the database during the flush time.
The flush operation takes every entity state change and translates it to an INSERT
, UPDATE
or DELETE
statement.
Because DML statements are grouped together, Hibernate can apply batching transparently. |
The flushing strategy is given by the flushMode
of the current running Hibernate Session
.
Although Jakarta Persistence defines only two flushing strategies (AUTO
and COMMIT
),
Hibernate has a much broader spectrum of flush types:
- ALWAYS
-
Flushes the
Session
before every query. - AUTO
-
This is the default mode, and it flushes the
Session
only if necessary. - COMMIT
-
The
Session
tries to delay the flush until the currentTransaction
is committed, although it might flush prematurely too. - MANUAL
-
The
Session
flushing is delegated to the application, which must callSession.flush()
explicitly in order to apply the persistence context changes.
6.1. AUTO
flush
By default, Hibernate uses the AUTO
flush mode which triggers a flush in the following circumstances:
-
prior to committing a
Transaction
-
prior to executing a JPQL/HQL query that overlaps with the queued entity actions
-
before executing any native SQL query that has no registered synchronization
6.1.1. AUTO
flush on commit
In the following example, an entity is persisted, and then the transaction is committed.
Example 422. Automatic flushing on commit
entityManager = entityManagerFactory().createEntityManager();
txn = entityManager.getTransaction();
txn.begin();
Person person = new Person("John Doe");
entityManager.persist(person);
log.info("Entity is in persisted state");
txn.commit();
--INFO: Entity is in persisted state
INSERT INTO Person (name, id) VALUES ('John Doe', 1)
Hibernate logs the message prior to inserting the entity because the flush only occurred during transaction commit.
This is valid for the |
6.1.2. AUTO
flush on JPQL/HQL query
A flush may also be triggered when executing an entity query.
Example 423. Automatic flushing on JPQL/HQL
Person person = new Person("John Doe");
entityManager.persist(person);
entityManager.createQuery("select p from Advertisement p").getResultList();
entityManager.createQuery("select p from Person p").getResultList();
SELECT a.id AS id1_0_ ,
a.title AS title2_0_
FROM Advertisement a
INSERT INTO Person (name, id) VALUES ('John Doe', 1)
SELECT p.id AS id1_1_ ,
p.name AS name2_1_
FROM Person p
The reason why the Advertisement
entity query didn’t trigger a flush is that there’s no overlapping between the Advertisement
and the Person
tables:
Example 424. Automatic flushing on JPQL/HQL entities
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
private String name;
//Getters and setters are omitted for brevity
}
@Entity(name = "Advertisement")
public static class Advertisement {
@Id
@GeneratedValue
private Long id;
private String title;
//Getters and setters are omitted for brevity
}
When querying for a Person
entity, the flush is triggered prior to executing the entity query.
Example 425. Automatic flushing on JPQL/HQL
Person person = new Person("John Doe");
entityManager.persist(person);
entityManager.createQuery("select p from Person p").getResultList();
INSERT INTO Person (name, id) VALUES ('John Doe', 1)
SELECT p.id AS id1_1_ ,
p.name AS name2_1_
FROM Person p
This time, the flush was triggered by a JPQL query because the pending entity persisting action overlaps with the query being executed.
6.1.3. AUTO
flush on native SQL query
When executing a native SQL query, a flush is always triggered when using the EntityManager
API.
Example 426. Automatic flushing on native SQL using EntityManager
assertTrue(((Number) entityManager
.createNativeQuery("select count(*) from Person")
.getSingleResult()).intValue() == 0);
Person person = new Person("John Doe");
entityManager.persist(person);
assertTrue(((Number) entityManager
.createNativeQuery("select count(*) from Person")
.getSingleResult()).intValue() == 1);
If you bootstrap Hibernate natively, and not through Jakarta Persistence, by default,
the Session
API will trigger a flush automatically when executing a native query.
Example 427. Automatic flushing on native SQL using Session
assertTrue(((Number) session
.createNativeQuery("select count(*) from Person", Integer.class)
.getSingleResult()).intValue() == 0);
Person person = new Person("John Doe");
session.persist(person);
assertTrue(((Number) session
.createNativeQuery("select count(*) from Person", Integer.class)
.uniqueResult()).intValue() == 0);
To flush the Session
, the query must use a synchronization:
Example 428. Automatic flushing on native SQL with Session
synchronization
assertTrue(((Number) entityManager
.createNativeQuery("select count(*) from Person")
.getSingleResult()).intValue() == 0);
Person person = new Person("John Doe");
entityManager.persist(person);
Session session = entityManager.unwrap(Session.class);
assertTrue(((Number) session
.createNativeQuery("select count(*) from Person", Integer.class)
.addSynchronizedEntityClass(Person.class)
.uniqueResult()).intValue() == 1);
6.2. COMMIT
flush
Jakarta Persistence also defines a COMMIT flush mode, which is described as follows:
If
FlushModeType.COMMIT
is set, the effect of updates made to entities in the persistence context upon queries is unspecified.
— Section 3.10.8 of the Java Persistence 2.1 Specification
When executing a JPQL query, the persistence context is only flushed when the current running transaction is committed.
Example 429. COMMIT
flushing on JPQL
Person person = new Person("John Doe");
entityManager.persist(person);
entityManager.createQuery("select p from Advertisement p")
.setFlushMode(FlushModeType.COMMIT)
.getResultList();
entityManager.createQuery("select p from Person p")
.setFlushMode(FlushModeType.COMMIT)
.getResultList();
SELECT a.id AS id1_0_ ,
a.title AS title2_0_
FROM Advertisement a
SELECT p.id AS id1_1_ ,
p.name AS name2_1_
FROM Person p
INSERT INTO Person (name, id) VALUES ('John Doe', 1)
Because the Jakarta Persistence doesn’t impose a strict rule on delaying flushing, when executing a native SQL query, the persistence context is going to be flushed.
Example 430. COMMIT
flushing on native SQL
Person person = new Person("John Doe");
entityManager.persist(person);
assertTrue(((Number) entityManager
.createNativeQuery("select count(*) from Person")
.getSingleResult()).intValue() == 1);
INSERT INTO Person (name, id) VALUES ('John Doe', 1)
SELECT COUNT(*) FROM Person
6.3. ALWAYS
flush
The |
The ALWAYS
flush mode triggers a persistence context flush even when executing a native SQL query against the Session
API.
Example 431. COMMIT
flushing on native SQL
Person person = new Person("John Doe");
entityManager.persist(person);
Session session = entityManager.unwrap(Session.class);
assertTrue(((Number) session
.createNativeQuery("select count(*) from Person", Integer.class)
.setHibernateFlushMode(FlushMode.ALWAYS)
.uniqueResult()).intValue() == 1);
INSERT INTO Person (name, id) VALUES ('John Doe', 1)
SELECT COUNT(*) FROM Person
6.4. MANUAL
flush
Both the EntityManager
and the Hibernate Session
define a flush()
method that, when called, triggers a manual flush.
Hibernate also provides a MANUAL
flush mode so the persistence context can only be flushed manually.
Example 432. MANUAL
flushing
Person person = new Person("John Doe");
entityManager.persist(person);
Session session = entityManager.unwrap(Session.class);
session.setHibernateFlushMode(FlushMode.MANUAL);
assertTrue(((Number) entityManager
.createQuery("select count(id) from Person")
.getSingleResult()).intValue() == 0);
assertTrue(((Number) session
.createNativeQuery("select count(*) from Person", Integer.class)
.uniqueResult()).intValue() == 0);
SELECT COUNT(p.id) AS col_0_0_
FROM Person p
SELECT COUNT(*)
FROM Person
The INSERT
statement was not executed because there was no manual flush()
call.
The |
6.5. Flush operation order
From a database perspective, a row state can be altered using either an INSERT
, an UPDATE
or a DELETE
statement.
Because entity state changes are automatically converted to SQL statements, it’s important to know which entity actions are associated with a given SQL statement.
INSERT
-
The
INSERT
statement is generated either by theEntityInsertAction
orEntityIdentityInsertAction
. These actions are scheduled by thepersist
operation, either explicitly or through cascading thePersistEvent
from a parent to a child entity. DELETE
-
The
DELETE
statement is generated by theEntityDeleteAction
orOrphanRemovalAction
. UPDATE
-
The
UPDATE
statement is generated byEntityUpdateAction
during flushing if the managed entity has been marked modified. The dirty checking mechanism is responsible for determining if a managed entity has been modified since it was first loaded.
Hibernate does not execute the SQL statements in the order of their associated entity state operations.
To visualize how this works, consider the following example:
Example 433. Flush operation order
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);
Person newPerson = new Person();
newPerson.setId(2L);
newPerson.setName("John Doe");
entityManager.persist(newPerson);
INSERT INTO Person (name, id)
VALUES ('John Doe', 2L)
DELETE FROM Person WHERE id = 1
Even if we removed the first entity and then persist a new one, Hibernate is going to execute the DELETE
statement after the INSERT
.
The order in which SQL statements are executed is given by the |
The ActionQueue
executes all operations in the following order:
-
OrphanRemovalAction
-
EntityInsertAction
orEntityIdentityInsertAction
-
EntityUpdateAction
-
QueuedOperationCollectionAction
-
CollectionRemoveAction
-
CollectionUpdateAction
-
CollectionRecreateAction
-
EntityDeleteAction
7. Database Access
7.1. ConnectionProvider
As an ORM tool, probably the single most important thing you need to tell Hibernate is how to connect to your database so that it may connect on behalf of your application.
This is ultimately the function of the org.hibernate.engine.jdbc.connections.spi.ConnectionProvider
interface.
Hibernate provides some out of the box implementations of this interface.
ConnectionProvider
is also an extension point so you can also use custom implementations from third parties or written yourself.
The ConnectionProvider
to use is defined by the hibernate.connection.provider_class
setting. See the org.hibernate.cfg.AvailableSettings#CONNECTION_PROVIDER
Generally speaking, applications should not have to configure a ConnectionProvider
explicitly if using one of the Hibernate-provided implementations.
Hibernate will internally determine which ConnectionProvider
to use based on the following algorithm:
-
If
hibernate.connection.provider_class
is set, it takes precedence -
else if
hibernate.connection.datasource
is set → Using DataSources -
else if any setting prefixed by
hibernate.c3p0.
is set → Using c3p0 -
else if any setting prefixed by
hibernate.proxool.
is set → Using Proxool -
else if any setting prefixed by
hibernate.hikari.
is set → Using HikariCP -
else if any setting prefixed by
hibernate.vibur.
is set → Using Vibur DBCP -
else if any setting prefixed by
hibernate.agroal.
is set → Using Agroal -
else if
hibernate.connection.url
is set → Using Hibernate’s built-in (and unsupported) pooling -
else → User-provided Connections
7.2. Using DataSources
Hibernate can integrate with a javax.sql.DataSource
for obtaining JDBC Connections.
Applications would tell Hibernate about the DataSource
via the (required) hibernate.connection.datasource
setting which can either specify a JNDI name or would reference the actual DataSource
instance.
For cases where a JNDI name is given, be sure to read JNDI.
For Jakarta Persistence applications, note that |
The DataSource
ConnectionProvider
also (optionally) accepts the hibernate.connection.username
and hibernate.connection.password
.
If specified, the DataSource#getConnection(String username, String password)
will be used.
Otherwise, the no-arg form is used.
7.3. Driver Configuration
hibernate.connection.driver_class
-
The name of the JDBC Driver class to use
hibernate.connection.url
-
The JDBC connection url
hibernate.connection.*
-
All such setting names (except the predefined ones) will have the
hibernate.connection.
prefix stripped. The remaining name and the original value will be passed to the driver as a JDBC connection property
Not all properties apply to all situations. For example, if you are providing a data source, hibernate.connection.driver_class setting will not be used.
|
7.4. Using c3p0
To use the c3p0 integration, the application must include the |
Hibernate also provides support for applications to use c3p0 connection pooling.
When c3p0 support is enabled, a number of c3p0-specific configuration settings are recognized in addition to the general ones described in Driver Configuration.
Transaction isolation of the Connections is managed by the ConnectionProvider
itself. See ConnectionProvider support for transaction isolation setting.
hibernate.c3p0.min_size
orc3p0.minPoolSize
-
The minimum size of the c3p0 pool. See c3p0 minPoolSize
hibernate.c3p0.max_size
orc3p0.maxPoolSize
-
The maximum size of the c3p0 pool. See c3p0 maxPoolSize
hibernate.c3p0.timeout
orc3p0.maxIdleTime
-
The Connection idle time. See c3p0 maxIdleTime
hibernate.c3p0.max_statements
orc3p0.maxStatements
-
Controls the c3p0 PreparedStatement cache size (if using). See c3p0 maxStatements
hibernate.c3p0.acquire_increment
orc3p0.acquireIncrement
-
Number of connections c3p0 should acquire at a time when the pool is exhausted. See c3p0 acquireIncrement
hibernate.c3p0.idle_test_period
orc3p0.idleConnectionTestPeriod
-
Idle time before a c3p0 pooled connection is validated. See c3p0 idleConnectionTestPeriod
hibernate.c3p0.initialPoolSize
-
The initial c3p0 pool size. If not specified, default is to use the min pool size. See c3p0 initialPoolSize
- Any other settings prefixed with
hibernate.c3p0.
-
Will have the
hibernate.
portion stripped and be passed to c3p0. - Any other settings prefixed with
c3p0.
-
Get passed to c3p0 as is. See c3p0 configuration
7.5. Using Proxool
To use the Proxool integration, the application must include the |
Hibernate also provides support for applications to use Proxool connection pooling.
Transaction isolation of the Connections is managed by the ConnectionProvider
itself. See ConnectionProvider support for transaction isolation setting.
7.5.1. Using existing Proxool pools
Controlled by the hibernate.proxool.existing_pool
setting.
If set to true, this ConnectionProvider will use an already existing Proxool pool by alias as indicated by the hibernate.proxool.pool_alias
setting.
7.5.2. Configuring Proxool via XML
The hibernate.proxool.xml
setting names a Proxool configuration XML file to be loaded as a classpath resource and loaded by Proxool’s JAXPConfigurator.
See proxool configuration.
hibernate.proxool.pool_alias
must be set to indicate which pool to use.
7.5.3. Configuring Proxool via Properties
The hibernate.proxool.properties
setting names a Proxool configuration properties file to be loaded as a classpath resource and loaded by Proxool’s PropertyConfigurator
.
See proxool configuration.
hibernate.proxool.pool_alias
must be set to indicate which pool to use.
7.6. Using HikariCP
To use the HikariCP this integration, the application must include the |
Hibernate also provides support for applications to use HikariCP connection pool.
Set all of your Hikari settings in Hibernate prefixed by hibernate.hikari.
and this ConnectionProvider
will pick them up and pass them along to Hikari.
Additionally, this ConnectionProvider
will pick up the following Hibernate-specific properties and map them to the corresponding Hikari ones (any hibernate.hikari.
prefixed ones have precedence):
hibernate.connection.driver_class
-
Mapped to Hikari’s
driverClassName
setting hibernate.connection.url
-
Mapped to Hikari’s
jdbcUrl
setting hibernate.connection.username
-
Mapped to Hikari’s
username
setting hibernate.connection.password
-
Mapped to Hikari’s
password
setting hibernate.connection.isolation
-
Mapped to Hikari’s
transactionIsolation
setting. See ConnectionProvider support for transaction isolation setting.
Note that Hikari only supports JDBC standard isolation levels (apparently). hibernate.connection.autocommit
-
Mapped to Hikari’s
autoCommit
setting
7.7. Using Vibur DBCP
To use the Vibur DBCP integration, the application must include the |
Hibernate also provides support for applications to use Vibur DBCP connection pool.
Set all of your Vibur settings in Hibernate prefixed by hibernate.vibur.
and this ConnectionProvider
will pick them up and pass them along to Vibur DBCP.
Additionally, this ConnectionProvider
will pick up the following Hibernate-specific properties and map them to the corresponding Vibur ones (any hibernate.vibur.
prefixed ones have precedence):
hibernate.connection.driver_class
-
Mapped to Vibur’s
driverClassName
setting hibernate.connection.url
-
Mapped to Vibur’s
jdbcUrl
setting hibernate.connection.username
-
Mapped to Vibur’s
username
setting hibernate.connection.password
-
Mapped to Vibur’s
password
setting hibernate.connection.isolation
-
Mapped to Vibur’s
defaultTransactionIsolationValue
setting. See ConnectionProvider support for transaction isolation setting. hibernate.connection.autocommit
-
Mapped to Vibur’s
defaultAutoCommit
setting
7.8. Using Agroal
To use the Agroal integration, the application must include the |
Hibernate also provides support for applications to use Agroal connection pool.
Set all of your Agroal settings in Hibernate prefixed by hibernate.agroal.
and this ConnectionProvider
will pick them up and pass them along to Agroal connection pool.
Additionally, this ConnectionProvider
will pick up the following Hibernate-specific properties and map them to the corresponding Agroal ones (any hibernate.agroal.
prefixed ones have precedence):
hibernate.connection.driver_class
-
Mapped to Agroal’s
driverClassName
setting hibernate.connection.url
-
Mapped to Agroal’s
jdbcUrl
setting hibernate.connection.username
-
Mapped to Agroal’s
principal
setting hibernate.connection.password
-
Mapped to Agroal’s
credential
setting hibernate.connection.isolation
-
Mapped to Agroal’s
jdbcTransactionIsolation
setting. See ConnectionProvider support for transaction isolation setting. hibernate.connection.autocommit
-
Mapped to Agroal’s
autoCommit
setting
7.9. Using Hibernate’s built-in (and unsupported) pooling
The built-in connection pool is not supported for use in a production system. |
This section is here just for completeness.
7.10. User-provided Connections
It is possible to use Hibernate by simply passing a Connection to use to the Session when the Session is opened.
This usage is discouraged and not discussed here.
7.11. ConnectionProvider support for transaction isolation setting
All the provided ConnectionProvider
implementations, apart from DataSourceConnectionProvider
, support consistent setting of transaction isolation for all Connections
obtained from the underlying pool.
The value for hibernate.connection.isolation
can be specified in one of 3 formats:
-
the integer value accepted at the JDBC level.
-
the name of the
java.sql.Connection
constant field representing the isolation you would like to use.
For example,TRANSACTION_REPEATABLE_READ
forjava.sql.Connection#TRANSACTION_REPEATABLE_READ
.
Note that this is only supported for JDBC standard isolation levels, not for isolation levels specific to a particular JDBC driver. -
a short-name version of the java.sql.Connection constant field without the
TRANSACTION_
prefix. For example,REPEATABLE_READ
forjava.sql.Connection#TRANSACTION_REPEATABLE_READ
.
Again, this is only supported for JDBC standard isolation levels, not for isolation levels specific to a particular JDBC driver.
7.12. Connection handling
The connection handling mode is defined by the
PhysicalConnectionHandlingMode
enumeration which provides the following strategies:
IMMEDIATE_ACQUISITION_AND_HOLD
-
The
Connection
will be acquired as soon as theSession
is opened and held until theSession
is closed. DELAYED_ACQUISITION_AND_HOLD
-
The
Connection
will be acquired as soon as it is needed and then held until theSession
is closed. DELAYED_ACQUISITION_AND_RELEASE_AFTER_STATEMENT
-
The
Connection
will be acquired as soon as it is needed and will be released after each statement is executed. DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION
-
The
Connection
will be acquired as soon as it is needed and will be released after each transaction is completed.
If you don’t want to use the default connection handling mode, you can specify a connection handling mode via the hibernate.connection.handling_mode
configuration property. For more details, check out the
Database connection properties section.
7.12.1. Transaction type and connection handling
By default, the connection handling mode is given by the underlying transaction coordinator. There are two types of transactions: RESOURCE_LOCAL
(which involves a single database Connection
and the transaction is controlled via the commit
and rollback
Connection
methods) and JTA
(which may involve multiple resources including database connections, JMS queues, etc).
RESOURCE_LOCAL transaction connection handling
For RESOURCE_LOCAL
transactions, the connection handling mode is DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION
meaning that the database connection is acquired when needed and released after the current running transaction is either committed or rolled back.
However, because Hibernate needs to make sure that the default autocommit mode is disabled on the JDBC Connection
when starting a new transaction, the Connection
is acquired and the autocommit mode is set to false
.
If you are using a connection pool |
JTA transaction connection handling
For JTA
transactions, the connection handling mode is DELAYED_ACQUISITION_AND_RELEASE_AFTER_STATEMENT
meaning that the database connection is acquired when needed and released after each statement execution.
The reason for releasing the database connection after statement execution is because some Java EE application servers
report a connection leak when a method call goes from one EJB to another. However, even if the JDBC Connection
is released to the pool, the Connection
is still allocated to the current executing Thread
, hence when executing a subsequent statement in the current running transaction, the same Connection
object reference will be obtained from the pool.
If the Java EE application server or JTA transaction manager supports switching from one EJB to another while the transaction gets propagated from the outer EJB to the inner one, |
7.12.2. User-provided connections
If the current Session
was created using the
SessionBuilder
and a JDBC Connection
was provided via the
SessionBuilder#connection
method, then the user-provided Connection
is going to be used, and
the connection handling mode will be IMMEDIATE_ACQUISITION_AND_HOLD
.
Therefore for user-provided connection, the connection is acquired right away and held until the current Session
is closed, without being influenced by the Jakarta Persistence or Hibernate transaction context.
7.13. Database Dialect
Although SQL is now relatively standardized—much more so than in the past—it’s still the case that each database vendor implements a different dialect of SQL that, while overlapping significantly with ANSI SQL, forms neither a subset, nor a superset, of the standard.
Hibernate abstracts over variations between dialects of SQL via the class org.hibernate.dialect.Dialect
.
-
There’s a subclass of
Dialect
for each supported relational database in the packageorg.hibernate.dialect
. -
Additional community-supported
Dialect
s are available in the separate modulehibernate-community-dialects
.
In Hibernate 6, it’s no longer necessary to explicitly specify a dialect using the configuration property hibernate.dialect
, and so setting that property is now discouraged.
(An exception is the case of custom user-written Dialect
s.)
8. Transactions
It is important to understand that the term transaction has many different yet related meanings in regards to persistence and Object/Relational Mapping.
In most use-cases these definitions align, but that is not always the case.
-
It might refer to the physical transaction with the database.
-
It might refer to the logical notion of a transaction as related to a persistence context.
-
It might refer to the application notion of a Unit-of-Work, as defined by the archetypal pattern.
This documentation largely treats the physical and logic notions of a transaction as one-in-the-same. |
8.1. Physical Transactions
Hibernate uses the JDBC API for persistence. In the world of Java, there are two well-defined mechanisms for dealing with transactions in JDBC: JDBC itself and JTA.
Hibernate supports both mechanisms for integrating with transactions and allowing applications to manage physical transactions.
The transaction handling per Session
is handled by the org.hibernate.resource.transaction.spi.TransactionCoordinator
contract,
which are built by the org.hibernate.resource.transaction.spi.TransactionCoordinatorBuilder
service.
TransactionCoordinatorBuilder
represents a strategy for dealing with transactions whereas TransactionCoordinator represents one instance of that strategy related to a Session.
Which TransactionCoordinatorBuilder
implementation to use is defined by the hibernate.transaction.coordinator_class
setting.
jdbc
(the default for non-Jakarta Persistence applications)-
Manages transactions via calls to
java.sql.Connection
jta
-
Manages transactions via JTA. See Java EE bootstrapping
If a Jakarta Persistence application does not provide a setting for hibernate.transaction.coordinator_class
, Hibernate will
automatically build the proper transaction coordinator based on the transaction type for the persistence unit.
If a non-Jakarta Persistence application does not provide a setting for hibernate.transaction.coordinator_class
, Hibernate
will use jdbc
as the default. This default will cause problems if the application actually uses JTA-based transactions.
A non-Jakarta Persistence application that uses JTA-based transactions should explicitly set hibernate.transaction.coordinator_class=jta
or provide a custom org.hibernate.resource.transaction.TransactionCoordinatorBuilder
that builds a
org.hibernate.resource.transaction.TransactionCoordinator
that properly coordinates with JTA-based transactions.
For details on implementing a custom |
Hibernate uses JDBC connections and JTA resources directly, without adding any additional locking behavior.
Hibernate does not lock objects in memory.
The behavior defined by the isolation level of your database transactions does not change when you use Hibernate.
The Hibernate Session
acts as a transaction-scoped cache providing repeatable reads for lookup by identifier and queries that result in loading entities.
To reduce lock contention in the database, the physical database transaction needs to be as short as possible. Long-running database transactions prevent your application from scaling to a highly-concurrent load. This concept is referred to as |
8.2. JTA configuration
Interaction with a JTA system is consolidated behind a single contract named org.hibernate.engine.transaction.jta.platform.spi.JtaPlatform
which exposes access to the javax.transaction.TransactionManager
and javax.transaction.UserTransaction
for that system as well as exposing the ability to register javax.transaction.Synchronization
instances, check transaction status, etc.
Generally, |
Hibernate tries to discover the JtaPlatform
it should use through the use of another service named org.hibernate.engine.transaction.jta.platform.spi.JtaPlatformResolver
.
If that resolution does not work, or if you wish to provide a custom implementation you will need to specify the hibernate.transaction.jta.platform
setting.
Hibernate provides many implementations of the JtaPlatform
contract, all with short names:
Atomikos
-
JtaPlatform
for Atomikos. Borland
-
JtaPlatform
for the Borland Enterprise Server. Bitronix
-
JtaPlatform
for Bitronix. JBossAS
-
JtaPlatform
for Arjuna/JBossTransactions/Narayana when used within the JBoss/WildFly Application Server. JBossTS
-
JtaPlatform
for Arjuna/JBossTransactions/Narayana when used standalone. JOnAS
-
JtaPlatform
for JOTM when used within JOnAS. JOTM
-
JtaPlatform
for JOTM when used standalone. JRun4
-
JtaPlatform
for the JRun 4 Application Server. OC4J
-
JtaPlatform
for Oracle’s OC4J container. Orion
-
JtaPlatform
for the Orion Application Server. Resin
-
JtaPlatform
for the Resin Application Server. SapNetWeaver
-
JtaPlatform
for the SAP NetWeaver Application Server. SunOne
-
JtaPlatform
for the SunOne Application Server. Weblogic
-
JtaPlatform
for the Weblogic Application Server. WebSphere
-
JtaPlatform
for older versions of the WebSphere Application Server. WebSphereExtended
-
JtaPlatform
for newer versions of the WebSphere Application Server.
8.3. Hibernate Transaction API
Hibernate provides an API for helping to isolate applications from the differences in the underlying physical transaction system in use.
Based on the configured TransactionCoordinatorBuilder
, Hibernate will simply do the right thing when this transaction API is used by the application.
This allows your applications and components to be more portable to move around into different environments.
To use this API, you would obtain the org.hibernate.Transaction
from the Session. Transaction
allows for all the normal operations you’d expect: begin
, commit
and rollback
, and it even exposes some cool methods like:
markRollbackOnly
-
that works in both JTA and JDBC.
getTimeout
andsetTimeout
-
that again work in both JTA and JDBC.
registerSynchronization
-
that allows you to register JTA Synchronizations even in non-JTA environments.
In fact, in both JTA and JDBC environments, theseSynchronizations
are kept locally by Hibernate.
In JTA environments, Hibernate will only ever register one singleSynchronization
with theTransactionManager
to avoid ordering problems.
Additionally, it exposes a getStatus method that returns an org.hibernate.resource.transaction.spi.TransactionStatus
enum.
This method checks with the underlying transaction system if needed, so care should be taken to minimize its use; it can have a big performance impact in certain JTA setups.
Let’s take a look at using the Transaction API in the various environments.
Example 434. Using Transaction API in JDBC
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
// "jdbc" is the default, but for explicitness
.applySetting(AvailableSettings.TRANSACTION_COORDINATOR_STRATEGY, "jdbc")
.build();
Metadata metadata = new MetadataSources(serviceRegistry)
.addAnnotatedClass(Customer.class)
.getMetadataBuilder()
.build();
SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
.build();
Session session = sessionFactory.openSession();
try {
// calls Connection#setAutoCommit(false) to
// signal start of transaction
session.getTransaction().begin();
session.createMutationQuery("UPDATE customer set NAME = 'Sir. '||NAME")
.executeUpdate();
// calls Connection#commit(), if an error
// happens we attempt a rollback
session.getTransaction().commit();
}
catch (Exception e) {
// we may need to rollback depending on
// where the exception happened
if (session.getTransaction().getStatus() == TransactionStatus.ACTIVE
|| session.getTransaction().getStatus() == TransactionStatus.MARKED_ROLLBACK) {
session.getTransaction().rollback();
}
// handle the underlying error
}
finally {
session.close();
sessionFactory.close();
}
Example 435. Using Transaction API in JTA (CMT)
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
// "jdbc" is the default, but for explicitness
.applySetting(AvailableSettings.TRANSACTION_COORDINATOR_STRATEGY, "jta")
.build();
Metadata metadata = new MetadataSources(serviceRegistry)
.addAnnotatedClass(Customer.class)
.getMetadataBuilder()
.build();
SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
.build();
// Note: depending on the JtaPlatform used and some optional settings,
// the underlying transactions here will be controlled through either
// the JTA TransactionManager or UserTransaction
Session session = sessionFactory.openSession();
try {
// Since we are in CMT, a JTA transaction would
// already have been started. This call essentially
// no-ops
session.getTransaction().begin();
Number customerCount = (Number) session.createSelectionQuery("select count(c) from Customer c").uniqueResult();
// Since we did not start the transaction (CMT),
// we also will not end it. This call essentially
// no-ops in terms of transaction handling.
session.getTransaction().commit();
}
catch (Exception e) {
// again, the rollback call here would no-op (aside from
// marking the underlying CMT transaction for rollback only).
if (session.getTransaction().getStatus() == TransactionStatus.ACTIVE
|| session.getTransaction().getStatus() == TransactionStatus.MARKED_ROLLBACK) {
session.getTransaction().rollback();
}
// handle the underlying error
}
finally {
session.close();
sessionFactory.close();
}
Example 436. Using Transaction API in JTA (BMT)
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
// "jdbc" is the default, but for explicitness
.applySetting(AvailableSettings.TRANSACTION_COORDINATOR_STRATEGY, "jta")
.build();
Metadata metadata = new MetadataSources(serviceRegistry)
.addAnnotatedClass(Customer.class)
.getMetadataBuilder()
.build();
SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
.build();
// Note: depending on the JtaPlatform used and some optional settings,
// the underlying transactions here will be controlled through either
// the JTA TransactionManager or UserTransaction
Session session = sessionFactory.openSession();
try {
// Assuming a JTA transaction is not already active,
// this call the TM/UT begin method. If a JTA
// transaction is already active, we remember that
// the Transaction associated with the Session did
// not "initiate" the JTA transaction and will later
// nop-op the commit and rollback calls...
session.getTransaction().begin();
session.persist(new Customer());
Customer customer = (Customer) session.createSelectionQuery("select c from Customer c").uniqueResult();
// calls TM/UT commit method, assuming we are initiator.
session.getTransaction().commit();
}
catch (Exception e) {
// we may need to rollback depending on
// where the exception happened
if (session.getTransaction().getStatus() == TransactionStatus.ACTIVE
|| session.getTransaction().getStatus() == TransactionStatus.MARKED_ROLLBACK) {
// calls TM/UT commit method, assuming we are initiator;
// otherwise marks the JTA transaction for rollback only
session.getTransaction().rollback();
}
// handle the underlying error
}
finally {
session.close();
sessionFactory.close();
}
In the CMT case, we really could have omitted all of the Transaction calls.
But the point of the examples was to show that the Transaction API really does insulate your code from the underlying transaction mechanism.
In fact, if you strip away the comments and the single configuration setting supplied at bootstrap, the code is exactly the same in all 3 examples.
In other words, we could develop that code and drop it, as-is, in any of the 3 transaction environments.
The Transaction API tries hard to make the experience consistent across all environments.
To that end, it generally defers to the JTA specification when there are differences (for example automatically trying rollback on a failed commit).
8.4. Contextual sessions
Most applications using Hibernate need some form of contextual session, where a given session is in effect throughout the scope of a given context.
However, across applications the definition of what constitutes a context is typically different; different contexts define different scopes to the notion of current.
Applications using Hibernate prior to version 3.0 tended to utilize either home-grown ThreadLocal
-based contextual sessions, helper classes such as HibernateUtil
, or utilized third-party frameworks, such as Spring or Pico, which provided proxy/interception-based contextual sessions.
Starting with version 3.0.1, Hibernate added the SessionFactory.getCurrentSession()
method.
Initially, this assumed usage of JTA
transactions, where the JTA
transaction defined both the scope and context of a current session.
Given the maturity of the numerous stand-alone JTA TransactionManager
implementations, most, if not all, applications should be using JTA
transaction management, whether or not they are deployed into a J2EE
container.
Based on that, the JTA
-based contextual sessions are all you need to use.
However, as of version 3.1, the processing behind SessionFactory.getCurrentSession()
is now pluggable.
To that end, a new extension interface, org.hibernate.context.spi.CurrentSessionContext
,
and a new configuration parameter, hibernate.current_session_context_class
, have been added to allow pluggability of the scope and context of defining current sessions.
See the Javadocs for the org.hibernate.context.spi.CurrentSessionContext
interface for a detailed discussion of its contract.
It defines a single method, currentSession()
, by which the implementation is responsible for tracking the current contextual session.
Out-of-the-box, Hibernate comes with three implementations of this interface:
org.hibernate.context.internal.JTASessionContext
-
current sessions are tracked and scoped by a
JTA
transaction.
The processing here is exactly the same as in the older JTA-only approach. org.hibernate.context.internal.ThreadLocalSessionContext
-
current sessions are tracked by thread of execution. See the Javadocs for more details.
org.hibernate.context.internal.ManagedSessionContext
-
current sessions are tracked by thread of execution.
However, you are responsible to bind and unbind aSession
instance with static methods on this class; it does not open, flush, or close aSession
.
Typically, the value of this parameter would just name the implementation class to use.
For the three out-of-the-box implementations, however, there are three corresponding short names: jta, thread, and managed.
The first two implementations provide a one session — one database transaction programming model.
This is also known and used as session-per-request.
The beginning and end of a Hibernate session is defined by the duration of a database transaction.
If you use programmatic transaction demarcation in plain Java SE without JTA, you are advised to use the Hibernate Transaction
API to hide the underlying transaction system from your code.
If you use JTA, you can utilize the JTA interfaces to demarcate transactions.
If you execute in an EJB container that supports CMT, transaction boundaries are defined declaratively and you do not need any transaction or session demarcation operations in your code.
The hibernate.current_session_context_class
configuration parameter defines which org.hibernate.context.spi.CurrentSessionContext
implementation should be used.
For backward compatibility, if this configuration parameter is not set but a org.hibernate.engine.transaction.jta.platform.spi.JtaPlatform
is configured, Hibernate will use the org.hibernate.context.internal.JTASessionContext
.
8.5. Transactional patterns (and anti-patterns)
8.5.1. Session-per-operation anti-pattern
This is an anti-pattern of opening and closing a Session
for each database call in a single thread.
It is also an anti-pattern in terms of database transactions.
Group your database calls into a planned sequence.
In the same way, do not auto-commit after every SQL statement in your application.
Hibernate disables or expects the application server to disable, auto-commit mode immediately.
Database transactions are never optional.
All communication with a database must be encapsulated by a transaction.
Avoid auto-commit behavior for reading data because many small transactions are unlikely to perform better than one clearly-defined unit of work, and are more difficult to maintain and extend.
Using auto-commit does not circumvent database transactions. Instead, when in auto-commit mode, JDBC drivers simply perform each call in an implicit transaction call. |
8.5.2. Session-per-request pattern
This is the most common transaction pattern.
The term request here relates to the concept of a system that reacts to a series of requests from a client/user.
Web applications are a prime example of this type of system, though certainly not the only one.
At the beginning of handling such a request, the application opens a Hibernate Session, starts a transaction, performs all data related work, ends the transaction and closes the Session.
The crux of the pattern is the one-to-one relationship between the transaction and the Session.
Within this pattern, there is a common technique of defining a current session to simplify the need of passing this Session
around to all the application components that may need access to it.
Hibernate provides support for this technique through the getCurrentSession
method of the SessionFactory
.
The concept of a current session has to have a scope that defines the bounds in which the notion of current is valid.
This is the purpose of the org.hibernate.context.spi.CurrentSessionContext
contract.
There are 2 reliable defining scopes:
-
First is a JTA transaction because it allows a callback hook to know when it is ending, which gives Hibernate a chance to close the
Session
and clean up.
This is represented by theorg.hibernate.context.internal.JTASessionContext
implementation of theorg.hibernate.context.spi.CurrentSessionContext
contract.
Using this implementation, aSession
will be opened the first timegetCurrentSession
is called within that transaction. -
Secondly is this application request cycle itself.
This is best represented with theorg.hibernate.context.internal.ManagedSessionContext
implementation of theorg.hibernate.context.spi.CurrentSessionContext
contract.
Here an external component is responsible for managing the lifecycle and scoping of a current session.
At the start of such a scope,ManagedSessionContext#bind()
method is called passing in theSession
.
In the end, itsunbind()
method is called.
Some common examples of such external components include:-
javax.servlet.Filter
implementation -
AOP interceptor with a pointcut on the service methods
-
A proxy/interception container
-
The |
8.5.3. Conversations (application-level transactions)
The session-per-request pattern is not the only valid way of designing units of work.
Many business processes require a whole series of interactions with the user that are interleaved with database accesses.
In web and enterprise applications, it is not acceptable for a database transaction to span a user interaction. Consider the following example:
The first screen of a dialog opens.
The data seen by the user is loaded in a particular Session
and database transaction.
The user is free to modify the objects.
The user uses a UI element to save their work after five minutes of editing.
The modifications are made persistent.
The user also expects to have exclusive access to the data during the edit session.
Even though we have multiple databases access here, from the point of view of the user, this series of steps represents a single unit of work.
There are many ways to implement this in your application.
A first naive implementation might keep the Session
and database transaction open while the user is editing, using database-level locks to prevent other users from modifying the same data and to guarantee isolation and atomicity.
This is an anti-pattern because lock contention is a bottleneck which will prevent scalability in the future.
Several database transactions are used to implement the conversation.
In this case, maintaining isolation of business processes becomes the partial responsibility of the application tier.
A single conversation usually spans several database transactions.
These multiple database accesses can only be atomic as a whole if only one of these database transactions (typically the last one) stores the updated data.
All others only read data.
A common way to receive this data is through a wizard-style dialog spanning several request/response cycles.
Hibernate includes some features which make this easy to implement.
Automatic Versioning |
Hibernate can perform automatic optimistic concurrency control for you. |
Detached Objects |
If you decide to use the session-per-request pattern, all loaded instances will be in the detached state during user think time. |
Extended |
The Hibernate |
Session-per-request-with-detached-objects and session-per-conversation each have advantages and disadvantages.
8.5.4. Session-per-application anti-pattern
The session-per-application is also considered an anti-pattern.
The Hibernate Session
, like the Jakarta Persistence EntityManager
, is not a thread-safe object and it is intended to be confined to a single thread at once.
If the Session
is shared among multiple threads, there will be race conditions as well as visibility issues, so beware of this.
An exception thrown by Hibernate means you have to rollback your database transaction and close the Session
immediately.
If your Session
is bound to the application, you have to stop the application.
Rolling back the database transaction does not put your business objects back into the state they were at the start of the transaction.
This means that the database state and the business objects will be out of sync.
Usually, this is not a problem because exceptions are not recoverable and you will have to start over after rollback anyway.
For more details, check out the exception handling section in Persistence Context chapter.
The Session
caches every object that is in a persistent state (watched and checked for dirty state by Hibernate).
If you keep it open for a long time or simply load too much data, it will grow endlessly until you get an OutOfMemoryException
.
One solution is to call clear()
and evict()
to manage the Session
cache, but you should consider a Stored Procedure if you need mass data operations.
Some solutions are shown in the Batching chapter.
Keeping a Session
open for the duration of a user session also means a higher probability of stale data.
9. JNDI
Hibernate does optionally interact with JNDI on the application’s behalf.
Generally, it does this when the application:
-
has asked the SessionFactory be bound to JNDI
-
has specified a DataSource to use by JNDI name
-
is using JTA transactions and the
JtaPlatform
needs to do JNDI lookups forTransactionManager
,UserTransaction
, etc
All of these JNDI calls route through a single service whose role is org.hibernate.engine.jndi.spi.JndiService
.
The standard JndiService
accepts a number of configuration settings:
-
hibernate.jndi.class
-
hibernate.jndi.url
Any other settings prefixed with hibernate.jndi.
will be collected and passed along to the JNDI provider.
The standard |
10. Locking
In a relational database, locking refers to actions taken to prevent data from changing between the time it is read and the time is used.
Your locking strategy can be either optimistic or pessimistic.
- Optimistic
-
Optimistic locking assumes that multiple transactions can complete without affecting each other,
and that therefore transactions can proceed without locking the data resources that they affect.
Before committing, each transaction verifies that no other transaction has modified its data.
If the check reveals conflicting modifications, the committing transaction rolls back. - Pessimistic
-
Pessimistic locking assumes that concurrent transactions will conflict with each other,
and requires resources to be locked after they are read and only unlocked after the application has finished using the data.
Hibernate provides mechanisms for implementing both types of locking in your applications.
10.1. Optimistic
When your application uses long transactions or conversations that span several database transactions,
you can store versioning data so that if the same entity is updated by two conversations, the last to commit changes is informed of the conflict,
and does not override the other conversation’s work.
This approach guarantees some isolation, but scales well and works particularly well in read-often-write-sometimes situations.
Hibernate provides two different mechanisms for storing versioning information, a dedicated version number or a timestamp.
A version or timestamp property can never be null for a detached instance. |
10.1.1. Mapping optimistic locking
Jakarta Persistence defines support for optimistic locking based on either a version (sequential numeric) or timestamp strategy.
To enable this style of optimistic locking simply add the jakarta.persistence.Version
to the persistent attribute that defines the optimistic locking value.
According to Jakarta Persistence, the valid types for these attributes are limited to:
-
int
orInteger
-
short
orShort
-
long
orLong
-
java.sql.Timestamp
However, Hibernate allows you to use even Java 8 Date/Time types, such as Instant
.
Example 437. @Version
annotation mapping
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@Column(name = "`name`")
private String name;
@Version
private long version;
//Getters and setters are omitted for brevity
}
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@Column(name = "`name`")
private String name;
@Version
private Timestamp version;
//Getters and setters are omitted for brevity
}
@Entity(name = "Person")
public static class Person {
@Id
@GeneratedValue
private Long id;
@Column(name = "`name`")
private String name;
@Version
private Instant version;
//Getters and setters are omitted for brevity
}
Dedicated version number
The version number mechanism for optimistic locking is provided through a @Version
annotation.
Example 438. @Version annotation
@Version
private long version;
Here, the version property is mapped to the version
column, and the entity manager uses it to detect conflicting updates,
and prevent the loss of updates that would otherwise be overwritten by a last-commit-wins strategy.
The version column can be any kind of type, as long as you define and implement the appropriate UserVersionType
.
Your application is forbidden from altering the version number set by Hibernate.
To artificially increase the version number, see the documentation for properties LockModeType.OPTIMISTIC_FORCE_INCREMENT
or
LockModeType.PESSIMISTIC_FORCE_INCREMENT
check in the Hibernate Entity Manager reference documentation.
If the version number is generated by the database, such as a trigger, use the annotation |
Timestamp
Timestamps are a less reliable way of optimistic locking than version numbers but can be used by applications for other purposes as well.
Timestamping is automatically used if you the @Version
annotation on a Date
or Calendar
property type.
Example 439. Using timestamps for optimistic locking
@Version
private Date version;
The timestamp can also be generated by the database, instead of by the VM, using the @CurrentTimestamp
annotation, or even @Generated(value = ALWAYS, sql = "current_timestamp")
.
Example 440. Database-generated version timestamp mapping
@Entity(name = "Person")
public static class Person {
@Id
private Long id;
private String firstName;
private String lastName;
@Version @CurrentTimestamp
private LocalDateTime version;
Now, when persisting a Person
entity, Hibernate calls the database-specific current timestamp retrieval function:
Example 441. Database-generated version timestamp example
Person person = new Person();
person.setId(1L);
person.setFirstName("John");
person.setLastName("Doe");
assertNull(person.getVersion());
entityManager.persist(person);
assertNotNull(person.getVersion());
CALL current_timestamp()
INSERT INTO
Person
(firstName, lastName, version, id)
VALUES
(?, ?, ?, ?)
-- binding parameter [1] as [VARCHAR] - [John]
-- binding parameter [2] as [VARCHAR] - [Doe]
-- binding parameter [3] as [TIMESTAMP] - [2017-05-18 12:03:03.808]
-- binding parameter [4] as [BIGINT] - [1]
Excluding attributes
By default, every entity attribute modification is going to trigger a version incrementation.
If there is an entity property which should not bump up the entity version,
then you need to annotate it with the Hibernate @OptimisticLock
annotation,
as illustrated in the following example.
Example 442. @OptimisticLock mapping example
@Entity(name = "Phone")
public static class Phone {
@Id
private Long id;
@Column(name = "`number`")
private String number;
@OptimisticLock(excluded = true)
private long callCount;
@Version
private Long version;
//Getters and setters are omitted for brevity
public void incrementCallCount() {
this.callCount++;
}
}
This way, if one thread modifies the Phone
number while a second thread increments the callCount
attribute,
the two concurrent transactions are not going to conflict as illustrated by the following example.
Example 443. @OptimisticLock exlude attribute example
doInJPA(this::entityManagerFactory, entityManager -> {
Phone phone = entityManager.find(Phone.class, 1L);
phone.setNumber("+123-456-7890");
doInJPA(this::entityManagerFactory, _entityManager -> {
Phone _phone = _entityManager.find(Phone.class, 1L);
_phone.incrementCallCount();
log.info("Bob changes the Phone call count");
});
log.info("Alice changes the Phone number");
});
-- Bob changes the Phone call count
update
Phone
set
callCount = 1,
"number" = '123-456-7890',
version = 0
where
id = 1
and version = 0
-- Alice changes the Phone number
update
Phone
set
callCount = 0,
"number" = '+123-456-7890',
version = 1
where
id = 1
and version = 0
When Bob changes the Phone
entity callCount
, the entity version is not bumped up.
That’s why Alice’s UPDATE succeeds since the entity version is still 0, even if Bob has changed the record
since Alice loaded it.
Although there is no conflict between Bob and Alice, Alice’s UPDATE overrides Bob’s change to the For this reason, you should only use this feature if you can accommodate lost updates on the excluded entity properties. |
Versionless optimistic locking
Although the default @Version
property optimistic locking mechanism is sufficient in many situations,
sometimes, you need rely on the actual database row column values to prevent lost updates.
Hibernate supports a form of optimistic locking that does not require a dedicated «version attribute».
This is also useful for use with modeling legacy schemas.
The idea is that you can get Hibernate to perform «version checks» using either all of the entity’s attributes or just the attributes that have changed.
This is achieved through the use of the
@OptimisticLocking
annotation which defines a single attribute of type
org.hibernate.annotations.OptimisticLockType
.
There are 4 available OptimisticLockTypes:
NONE
-
optimistic locking is disabled even if there is a
@Version
annotation present VERSION
(the default)-
performs optimistic locking based on a
@Version
as described above ALL
-
performs optimistic locking based on all fields as part of an expanded WHERE clause restriction for the UPDATE/DELETE SQL statements
DIRTY
-
performs optimistic locking based on dirty fields as part of an expanded WHERE clause restriction for the UPDATE/DELETE SQL statements
Versionless optimistic locking using OptimisticLockType.ALL
Example 444. OptimisticLockType.ALL
mapping example
@Entity(name = "Person")
@OptimisticLocking(type = OptimisticLockType.ALL)
@DynamicUpdate
public static class Person {
@Id
private Long id;
@Column(name = "`name`")
private String name;
private String country;
private String city;
@Column(name = "created_on")
private Timestamp createdOn;
//Getters and setters are omitted for brevity
}
When you need to modify the Person
entity above:
Example 445. OptimisticLockType.ALL
update example
Person person = entityManager.find(Person.class, 1L);
person.setCity("Washington D.C.");
UPDATE
Person
SET
city=?
WHERE
id=?
AND city=?
AND country=?
AND created_on=?
AND "name"=?
-- binding parameter [1] as [VARCHAR] - [Washington D.C.]
-- binding parameter [2] as [BIGINT] - [1]
-- binding parameter [3] as [VARCHAR] - [New York]
-- binding parameter [4] as [VARCHAR] - [US]
-- binding parameter [5] as [TIMESTAMP] - [2016-11-16 16:05:12.876]
-- binding parameter [6] as [VARCHAR] - [John Doe]
As you can see, all the columns of the associated database row are used in the WHERE
clause.
If any column has changed after the row was loaded, there won’t be any match, and a StaleStateException
or an OptimisticEntityLockException
is going to be thrown.
When using |
Versionless optimistic locking using OptimisticLockType.DIRTY
The OptimisticLockType.DIRTY
differs from OptimisticLockType.ALL
in that it only takes into consideration the entity properties that have changed
since the entity was loaded in the currently running Persistence Context.
Example 446. OptimisticLockType.DIRTY
mapping example
@Entity(name = "Person")
@OptimisticLocking(type = OptimisticLockType.DIRTY)
@DynamicUpdate
public static class Person {
@Id
private Long id;
@Column(name = "`name`")
private String name;
private String country;
private String city;
@Column(name = "created_on")
private Timestamp createdOn;
//Getters and setters are omitted for brevity
}
When you need to modify the Person
entity above:
Example 447. OptimisticLockType.DIRTY
update example
Person person = entityManager.find(Person.class, 1L);
person.setCity("Washington D.C.");
UPDATE
Person
SET
city=?
WHERE
id=?
and city=?
-- binding parameter [1] as [VARCHAR] - [Washington D.C.]
-- binding parameter [2] as [BIGINT] - [1]
-- binding parameter [3] as [VARCHAR] - [New York]
This time, only the database column that has changed was used in the WHERE
clause.
The main advantage of When using |
10.2. Pessimistic
Typically, you only need to specify an isolation level for the JDBC connections and let the database handle locking issues.
If you do need to obtain exclusive pessimistic locks or re-obtain locks at the start of a new transaction, Hibernate gives you the tools you need.
Hibernate always uses the locking mechanism of the database, and never lock objects in memory. |
10.3. LockMode
and LockModeType
Long before Java Persistence 1.0, Hibernate already defined various explicit locking strategies through its LockMode
enumeration.
Jakarta Persistence comes with its own LockModeType
enumeration which defines similar strategies as the Hibernate-native LockMode
.
LockModeType |
LockMode |
Description |
---|---|---|
|
|
The absence of a lock. All objects switch to this lock mode at the end of a Transaction. Objects associated with the session via a call to |
|
|
The entity version is checked towards the end of the currently running transaction. |
|
|
The entity version is incremented automatically even if the entity has not changed. |
|
|
The entity is locked pessimistically and its version is incremented automatically even if the entity has not changed. |
|
|
The entity is locked pessimistically using a shared lock if the database supports such a feature. Otherwise, an explicit lock is used. |
|
|
The entity is locked using an explicit lock. |
|
|
The lock acquisition request fails fast if the row s already locked. |
|
|
The lock acquisition request skips the already locked rows. It uses a |
The explicit user request mentioned above occurs as a consequence of any of the following actions:
-
a call to
Session.load()
, specifying aLockMode
. -
a call to
Session.lock()
. -
a call to
Query.setLockMode()
.
If you call Session.load()
with option UPGRADE
, UPGRADE_NOWAIT
or UPGRADE_SKIPLOCKED
,
and the requested object is not already loaded by the session, the object is loaded using SELECT … FOR UPDATE
.
If you call load()
for an object that is already loaded with a less restrictive lock than the one you request, Hibernate calls lock()
for that object.
Session.lock(
) performs a version number check if the specified lock mode is READ
, UPGRADE
, UPGRADE_NOWAIT
or UPGRADE_SKIPLOCKED
.
In the case of UPGRADE
, UPGRADE_NOWAIT
or UPGRADE_SKIPLOCKED
, the SELECT … FOR UPDATE
syntax is used.
If the requested lock mode is not supported by the database, Hibernate uses an appropriate alternate mode instead of throwing an exception.
This ensures that applications are portable.
10.4. Jakarta Persistence locking query hints
Jakarta Persistence defined two locking-related query hints:
- jakarta.persistence.lock.timeout
-
it gives the number of milliseconds a lock acquisition request will wait before throwing an exception
- jakarta.persistence.lock.scope
-
defines the scope of the lock acquisition request.
The scope can either beNORMAL
(default value) orEXTENDED
. TheEXTENDED
scope will cause a lock acquisition request to be passed to other owned table structured (e.g.@Inheritance(strategy=InheritanceType.JOINED)
,@ElementCollection
)
Example 448. jakarta.persistence.lock.timeout
example
entityManager.find(
Person.class, id, LockModeType.PESSIMISTIC_WRITE,
Collections.singletonMap("jakarta.persistence.lock.timeout", 200)
);
SELECT explicitlo0_.id AS id1_0_0_,
explicitlo0_."name" AS name2_0_0_
FROM person explicitlo0_
WHERE explicitlo0_.id = 1
FOR UPDATE wait 2
Not all JDBC database drivers support setting a timeout value for a locking request. |
The |
10.5. Session.lock()
The following example shows how to obtain a shared database lock.
Example 449. session.lock()
example
Person person = entityManager.find(Person.class, id);
Session session = entityManager.unwrap(Session.class);
LockOptions lockOptions = new LockOptions(LockMode.PESSIMISTIC_READ, LockOptions.NO_WAIT);
session.lock(person, lockOptions);
SELECT p1_0.id,
p1_0."name"
FROM Person p1_0
WHERE p1_0.id = 1
SELECT id
FROM Person
WHERE id = 1
FOR UPDATE
10.6. Follow-on-locking
-
DISTINCT
-
GROUP BY
-
UNION
-
inlined views (derived tables), therefore, affecting the legacy Oracle pagination mechanism as well.
For this reason, Hibernate uses secondary selects to lock the previously fetched entities.
Example 450. Follow-on-locking example
List<Person> persons = entityManager.createQuery(
"select DISTINCT p from Person p", Person.class)
.setLockMode(LockModeType.PESSIMISTIC_WRITE)
.getResultList();
SELECT DISTINCT p.id as id1_0_, p."name" as name2_0_
FROM Person p
SELECT id
FROM Person
WHERE id = 1 FOR UPDATE
SELECT id
FROM Person
WHERE id = 2 FOR UPDATE
To avoid the N+1 query problem, a separate query can be used to apply the lock using the associated entity identifiers. |
Example 451. Secondary query entity locking
List<Person> persons = entityManager.createQuery(
"select DISTINCT p from Person p", Person.class)
.getResultList();
entityManager.createQuery(
"select p.id from Person p where p in :persons")
.setLockMode(LockModeType.PESSIMISTIC_WRITE)
.setParameter("persons", persons)
.getResultList();
SELECT DISTINCT p.id as id1_0_, p."name" as name2_0_
FROM Person p
SELECT p.id as col_0_0_
FROM Person p
WHERE p.id IN ( 1 , 2 )
FOR UPDATE
The lock request was moved from the original query to a secondary one which takes the previously fetched entities to lock their associated database records.
Prior to Hibernate 5.2.1, the follow-on-locking mechanism was applied uniformly to any locking query executing on Oracle.
Since 5.2.1, the Oracle Dialect tries to figure out if the current query demands the follow-on-locking mechanism.
Even more important is that you can overrule the default follow-on-locking detection logic and explicitly enable or disable it on a per query basis.
Example 452. Disabling the follow-on-locking mechanism explicitly
List<Person> persons = entityManager.createQuery(
"select p from Person p", Person.class)
.setMaxResults(10)
.unwrap(Query.class)
.setLockOptions(
new LockOptions(LockMode.PESSIMISTIC_WRITE)
.setFollowOnLocking(false))
.getResultList();
SELECT *
FROM (
SELECT p.id as id1_0_, p."name" as name2_0_
FROM Person p
)
WHERE rownum <= 10
FOR UPDATE
The follow-on-locking mechanism should be explicitly enabled only if the currently executing query fails because the |
11. Fetching
Fetching, essentially, is the process of grabbing data from the database and making it available to the application.
Tuning how an application does fetching is one of the biggest factors in determining how an application will perform.
Fetching too much data, in terms of width (values/columns) and/or depth (results/rows),
adds unnecessary overhead in terms of both JDBC communication and ResultSet processing.
Fetching too little data might cause additional fetching to be needed.
Tuning how an application fetches data presents a great opportunity to influence the overall application performance.
11.1. The basics
The concept of fetching breaks down into two different questions.
-
When should the data be fetched? Now? Later?
-
How should the data be fetched?
«Now» is generally termed eager or immediate while «later» is generally termed lazy or delayed. |
There are a number of scopes for defining fetching:
- static
-
Static definition of fetching strategies is done in the mappings.
The statically-defined fetch strategies are used in the absence of any dynamically defined strategies.- SELECT
-
Performs a separate SQL select to load the data. This can either be EAGER (the second select is issued immediately) or LAZY (the second select is delayed until the data is needed).
This is the strategy generally termed N+1. - JOIN
-
Inherently an EAGER style of fetching. The data to be fetched is obtained through the use of an SQL outer join.
- BATCH
-
Performs a separate SQL select to load a number of related data items using an IN-restriction as part of the SQL WHERE-clause based on a batch size.
Again, this can either be EAGER (the second select is issued immediately) or LAZY (the second select is delayed until the data is needed). - SUBSELECT
-
Performs a separate SQL select to load associated data based on the SQL restriction used to load the owner.
Again, this can either be EAGER (the second select is issued immediately) or LAZY (the second select is delayed until the data is needed).
- dynamic (sometimes referred to as runtime)
-
The dynamic definition is really use-case centric. There are multiple ways to define dynamic fetching:
- fetch profiles
-
defined in mappings, but can be enabled/disabled on the
Session
. - HQL / JPQL
-
both Hibernate and Jakarta Persistence Criteria queries have the ability to specify fetching, specific to said query.
- entity graphs
-
using Jakarta Persistence EntityGraphs
|
11.2. Direct fetching vs. entity queries
To see the difference between direct fetching and entity queries in regard to eagerly fetched associations, consider the following entities:
Example 453. Domain model
@Entity(name = "Department")
public static class Department {
@Id
private Long id;
//Getters and setters omitted for brevity
}
@Entity(name = "Employee")
public static class Employee {
@Id
private Long id;
@NaturalId
private String username;
@ManyToOne(fetch = FetchType.EAGER)
private Department department;
//Getters and setters omitted for brevity
}
The Employee
entity has a @ManyToOne
association to a Department
which is fetched eagerly.
When issuing a direct entity fetch, Hibernate executed the following SQL query:
Example 454. Direct fetching example
Employee employee = entityManager.find(Employee.class, 1L);
select
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.username as username2_1_0_,
d.id as id1_0_1_
from
Employee e
left outer join
Department d
on e.department_id=d.id
where
e.id = 1
The LEFT OUTER JOIN
clause is added to the generated SQL query because this association is required to be fetched eagerly.
On the other hand, if you are using an entity query that does not contain a JOIN FETCH
directive to the Department
association:
Example 455. Entity query fetching example
Employee employee = entityManager.createQuery(
"select e " +
"from Employee e " +
"where e.id = :id", Employee.class)
.setParameter("id", 1L)
.getSingleResult();
select
e.id as id1_1_,
e.department_id as departme3_1_,
e.username as username2_1_
from
Employee e
where
e.id = 1
select
d.id as id1_0_0_
from
Department d
where
d.id = 1
Hibernate uses a secondary select instead. This is because the entity query fetch policy cannot be overridden,
so Hibernate requires a secondary select to ensure that the EAGER association is fetched prior to returning the result to the user.
If you forget to JOIN FETCH all EAGER associations, Hibernate is going to issue a secondary select for each and every one of those For this reason, you should prefer LAZY associations. |
11.3. Applying fetch strategies
Let’s consider these topics as it relates to a sample domain model and a few use cases.
Example 456. Sample domain model
@Entity(name = "Department")
public static class Department {
@Id
private Long id;
@OneToMany(mappedBy = "department")
private List<Employee> employees = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Employee")
public static class Employee {
@Id
private Long id;
@NaturalId
private String username;
@Column(name = "pswd")
@ColumnTransformer(
read = "decrypt('AES', '00', pswd )",
write = "encrypt('AES', '00', ?)"
)
// For H2 2.0.202+ one must use the varbinary DDL type
// @Column(name = "pswd", columnDefinition = "varbinary")
// @ColumnTransformer(
// read = "trim(trailing u&'\\0000' from cast(decrypt('AES', '00', pswd ) as character varying))",
// write = "encrypt('AES', '00', ?)"
// )
private String password;
private int accessLevel;
@ManyToOne(fetch = FetchType.LAZY)
private Department department;
@ManyToMany(mappedBy = "employees")
private List<Project> projects = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Project")
public class Project {
@Id
private Long id;
@ManyToMany
private List<Employee> employees = new ArrayList<>();
//Getters and setters omitted for brevity
}
The Hibernate recommendation is to statically mark all associations lazy and to use dynamic fetching strategies for eagerness. This is unfortunately at odds with the Jakarta Persistence specification which defines that all one-to-one and many-to-one associations should be eagerly fetched by default. Hibernate, as a Jakarta Persistence provider, honors that default. |
11.4. No fetching
For the first use case, consider the application login process for an Employee
.
Let’s assume that login only requires access to the Employee
information, not Project
nor Department
information.
Example 457. No fetching example
Employee employee = entityManager.createQuery(
"select e " +
"from Employee e " +
"where " +
" e.username = :username and " +
" e.password = :password",
Employee.class)
.setParameter("username", username)
.setParameter("password", password)
.getSingleResult();
In this example, the application gets the Employee
data.
However, because all associations from Employee
are declared as LAZY (Jakarta Persistence defines the default for collections as LAZY) no other data is fetched.
If the login process does not need access to the Employee
information specifically, another fetching optimization here would be to limit the width of the query results.
Example 458. No fetching (scalar) example
Integer accessLevel = entityManager.createQuery(
"select e.accessLevel " +
"from Employee e " +
"where " +
" e.username = :username and " +
" e.password = :password",
Integer.class)
.setParameter("username", username)
.setParameter("password", password)
.getSingleResult();
11.5. Dynamic fetching via queries
For the second use case, consider a screen displaying the Projects
for an Employee
.
Certainly access to the Employee
is needed, as is the collection of Projects
for that Employee. Information about Departments
, other Employees
or other Projects
is not needed.
Example 459. Dynamic JPQL fetching example
Employee employee = entityManager.createQuery(
"select e " +
"from Employee e " +
"left join fetch e.projects " +
"where " +
" e.username = :username and " +
" e.password = :password",
Employee.class)
.setParameter("username", username)
.setParameter("password", password)
.getSingleResult();
Example 460. Dynamic query fetching example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> query = builder.createQuery(Employee.class);
Root<Employee> root = query.from(Employee.class);
root.fetch("projects", JoinType.LEFT);
query.select(root).where(
builder.and(
builder.equal(root.get("username"), username),
builder.equal(root.get("password"), password)
)
);
Employee employee = entityManager.createQuery(query).getSingleResult();
In this example we have an Employee
and their Projects
loaded in a single query shown both as an HQL query and a Jakarta Persistence Criteria query.
In both cases, this resolves to exactly one database query to get all that information.
11.6. Dynamic fetching via Jakarta Persistence entity graph
Jakarta Persistence also supports a feature called EntityGraphs to provide the application developer has more control over fetch plans. It has two modes to choose from:
- fetch graph
-
In this case, all attributes specified in the entity graph will be treated as FetchType.EAGER, and all attributes not specified will ALWAYS be treated as FetchType.LAZY.
- load graph
-
In this case, all attributes specified in the entity graph will be treated as FetchType.EAGER, but attributes not specified use their static mapping specification.
Below is a fetch graph
dynamic fetching example:
Example 461. Fetch graph example
@Entity(name = "Employee")
@NamedEntityGraph(name = "employee.projects",
attributeNodes = @NamedAttributeNode("projects")
)
Employee employee = entityManager.find(
Employee.class,
userId,
Collections.singletonMap(
"jakarta.persistence.fetchgraph",
entityManager.getEntityGraph("employee.projects")
)
);
When executing a JPQL query, if an EAGER association is omitted, Hibernate will issue a secondary select for every association needed to be fetched eagerly, For this reason, it’s better to use LAZY associations, and only fetch them eagerly on a per-query basis. |
An EntityGraph is the root of a «load plan» and must correspond to an EntityType.
11.6.1. Jakarta Persistence (key) subgraphs
A sub-graph is used to control the fetching of sub-attributes of the AttributeNode it is applied to.
It is generally defined via the @NamedSubgraph
annotation.
If we have a Project
parent entity which has an employees
child associations,
and we’d like to fetch the department
for the Employee
child association.
Example 462. Fetch graph with a subgraph mapping
@Entity(name = "Project")
@NamedEntityGraph(name = "project.employees",
attributeNodes = @NamedAttributeNode(
value = "employees",
subgraph = "project.employees.department"
),
subgraphs = @NamedSubgraph(
name = "project.employees.department",
attributeNodes = @NamedAttributeNode("department")
)
)
public static class Project {
@Id
private Long id;
@ManyToMany
private List<Employee> employees = new ArrayList<>();
//Getters and setters omitted for brevity
}
When fetching this entity graph, Hibernate generates the following SQL query:
Example 463. Fetch graph with a subgraph mapping
Project project = doInJPA(this::entityManagerFactory, entityManager -> {
return entityManager.find(
Project.class,
1L,
Collections.singletonMap(
"jakarta.persistence.fetchgraph",
entityManager.getEntityGraph("project.employees")
)
);
});
select
p.id as id1_2_0_, e.id as id1_1_1_, d.id as id1_0_2_,
e.accessLevel as accessLe2_1_1_,
e.department_id as departme5_1_1_,
decrypt( 'AES', '00', e.pswd ) as pswd3_1_1_,
e.username as username4_1_1_,
p_e.projects_id as projects1_3_0__,
p_e.employees_id as employee2_3_0__
from
Project p
inner join
Project_Employee p_e
on p.id=p_e.projects_id
inner join
Employee e
on p_e.employees_id=e.id
inner join
Department d
on e.department_id=d.id
where
p.id = ?
-- binding parameter [1] as [BIGINT] - [1]
Specifying a sub-graph is only valid for an attribute (or its «key») whose type is a ManagedType. So
while an EntityGraph must correspond to an EntityType, a Subgraph is legal for any ManagedType. An
attribute’s key is defined as either:
-
For a singular attribute, the attribute’s type must be an IdentifiableType and that IdentifiableType must
have a composite identifier. The «key sub-graph» is applied to the identifier type. The
non-key sub-graph applies to the attribute’s value, which must be a ManagedType. -
For a plural attribute, the attribute must be a Map and the Map’s key value must be a ManagedType.
The «key sub-graph» is applied to the Map’s key type. In this case, the non-key sub-graph applies
to the plural attribute’s value/element.
11.6.2. Jakarta Persistence SubGraph sub-typing
SubGraphs can also be sub-type specific. Given an attribute whose value is an inheritance hierarchy,
we can refer to attributes of a specific sub-type using the forms of sub-graph definition that accept
the sub-type Class.
11.6.3. Creating and applying Jakarta Persistence graphs from text representations
Hibernate allows the creation of Jakarta Persistence fetch/load graphs by parsing a textual representation
of the graph. Generally speaking, the textual representation of a graph is a comma-separated
list of attribute names, optionally including any sub-graph specifications.
org.hibernate.graph.EntityGraphParser
is the starting point for such parsing operations.
Parsing a textual representation of a graph is not (yet) a part of the Jakarta Persistence specification. So the |
Example 464. Parsing a simple graph
final EntityGraph<Project> graph = GraphParser.parse(
Project.class,
"employees(department)",
entityManager
);
This example actually functions exactly as Fetch graph with a subgraph mapping,
just using a parsed graph rather than a named graph.
The syntax also supports defining «key sub-graphs». To specify a key sub-graph, .key
is added
to the end of the attribute name.
Example 465. Parsing an entity key graph
final EntityGraph<Movie> graph = GraphParser.parse(
Movie.class,
"cast.key(name)",
entityManager
);
Example 466. Parsing a map key graph
final EntityGraph<Ticket> graph = GraphParser.parse(
Ticket.class,
"showing.key(movie(cast))",
entityManager
);
Parsing can also handle sub-type specific sub-graphs. For example, given an entity hierarchy of
LegalEntity
← (Corporation
| Person
| NonProfit
) and an attribute named responsibleParty
whose
type is the LegalEntity
base type we might have:
responsibleParty(Corporation: ceo)
We can even duplicate the attribute names to apply different sub-type sub-graphs:
responsibleParty(taxIdNumber), responsibleParty(Corporation: ceo), responsibleParty(NonProfit: sector)
The duplicated attribute names are handled according to the Jakarta Persistence specification which says that duplicate
specification of the attribute node results in the originally registered AttributeNode to be re-used
effectively merging the 2 AttributeNode specifications together. In other words, the above specification
creates a single AttributeNode with 3 distinct SubGraphs. It is functionally the same as calling:
Class<Invoice> invoiceClass = ...;
jakarta.persistence.EntityGraph<Invoice> invoiceGraph = entityManager.createEntityGraph( invoiceClass );
invoiceGraph.addAttributeNode( "responsibleParty" );
invoiceGraph.addSubgraph( "responsibleParty" ).addAttributeNode( "taxIdNumber" );
invoiceGraph.addSubgraph( "responsibleParty", Corporation.class ).addAttributeNode( "ceo" );
invoiceGraph.addSubgraph( "responsibleParty", NonProfit.class ).addAttributeNode( "sector" );
11.6.4. Combining multiple Jakarta Persistence entity graphs into one
Multiple entity graphs can be combined into a single «super graph» that acts as a union. Graph from
the previous example can also be built by combining separate aspect graphs into one, such as:
Example 467. Combining multiple graphs into one
final EntityGraph<Project> a = GraphParser.parse(
Project.class, "employees(username)", entityManager
);
final EntityGraph<Project> b = GraphParser.parse(
Project.class, "employees(password, accessLevel)", entityManager
);
final EntityGraph<Project> c = GraphParser.parse(
Project.class, "employees(department(employees(username)))", entityManager
);
final EntityGraph<Project> all = EntityGraphs.merge(entityManager, Project.class, a, b, c);
11.7. Dynamic fetching via Hibernate profiles
Suppose we wanted to leverage loading by natural-id to obtain the Employee
information in the «projects for and employee» use-case.
Loading by natural-id uses the statically defined fetching strategies, but does not expose a means to define load-specific fetching.
So we would leverage a fetch profile.
Example 468. Fetch profile example
@Entity(name = "Employee")
@FetchProfile(
name = "employee.projects",
fetchOverrides = {
@FetchProfile.FetchOverride(
entity = Employee.class,
association = "projects",
mode = FetchMode.JOIN
)
}
)
session.enableFetchProfile("employee.projects");
Employee employee = session.bySimpleNaturalId(Employee.class).load(username);
Here the Employee
is obtained by natural-id lookup and the Employee’s Project
data is fetched eagerly.
If the Employee
data is resolved from cache, the Project
data is resolved on its own.
However, if the Employee
data is not resolved in cache, the Employee
and Project
data is resolved in one SQL query via join as we saw above.
11.8. Batch fetching
Hibernate offers the @BatchSize
annotation,
which can be used when fetching uninitialized entity proxies.
Considering the following entity mapping:
Example 469. @BatchSize
mapping example
@Entity(name = "Department")
public static class Department {
@Id
private Long id;
@OneToMany(mappedBy = "department")
//@BatchSize(size = 5)
private List<Employee> employees = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Employee")
public static class Employee {
@Id
private Long id;
@NaturalId
private String name;
@ManyToOne(fetch = FetchType.LAZY)
private Department department;
//Getters and setters omitted for brevity
}
Considering that we have previously fetched several Department
entities,
and now we need to initialize the employees
entity collection for each particular Department
,
the @BatchSize
annotations allows us to load multiple Employee
entities in a single database roundtrip.
Example 470. @BatchSize
fetching example
List<Department> departments = entityManager.createQuery(
"select d " +
"from Department d " +
"inner join d.employees e " +
"where e.name like 'John%'", Department.class)
.getResultList();
for (Department department : departments) {
log.infof(
"Department %d has {} employees",
department.getId(),
department.getEmployees().size()
);
}
SELECT
d.id as id1_0_
FROM
Department d
INNER JOIN
Employee employees1_
ON d.id=employees1_.department_id
SELECT
e.department_id as departme3_1_1_,
e.id as id1_1_1_,
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.name as name2_1_0_
FROM
Employee e
WHERE
e.department_id IN (
0, 2, 3, 4, 5
)
SELECT
e.department_id as departme3_1_1_,
e.id as id1_1_1_,
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.name as name2_1_0_
FROM
Employee e
WHERE
e.department_id IN (
6, 7, 8, 9, 1
)
As you can see in the example above, there are only two SQL statements used to fetch the Employee
entities associated with multiple Department
entities.
Without However, although |
When This because the lock mode is different from the one of the proxies in the batch fetch queue. |
11.9. The @Fetch
annotation mapping
Besides the FetchType.LAZY
or FetchType.EAGER
Jakarta Persistence annotations,
you can also use the Hibernate-specific @Fetch
annotation that accepts one of the following FetchMode
s:
- SELECT
-
The association is going to be fetched using a secondary select for each individual entity,
collection, or join load. This mode can be used for eitherFetchType.EAGER
orFetchType.LAZY
. - JOIN
-
Use an outer join to load the related entities, collections or joins when using direct fetching. This mode
can only be used forFetchType.EAGER
. - SUBSELECT
-
Available for collections only. When accessing a non-initialized collection,
this fetch mode will trigger loading all elements of all collections of the same role for all owners associated
with the persistence context using a single secondary select.
11.10. FetchMode.SELECT
To demonstrate how FetchMode.SELECT
works, consider the following entity mapping:
Example 471. FetchMode.SELECT
mapping example
@Entity(name = "Department")
public static class Department {
@Id
private Long id;
@OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
@Fetch(FetchMode.SELECT)
private List<Employee> employees = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Employee")
public static class Employee {
@Id
@GeneratedValue
private Long id;
@NaturalId
private String username;
@ManyToOne(fetch = FetchType.LAZY)
private Department department;
//Getters and setters omitted for brevity
}
Considering there are multiple Department
entities, each one having multiple Employee
entities,
when executing the following test case, Hibernate fetches every uninitialized Employee
collection using a secondary SELECT
statement upon accessing the child collection for the first time:
Example 472. FetchMode.SELECT
mapping example
List<Department> departments = entityManager.createQuery(
"select d from Department d", Department.class)
.getResultList();
log.infof("Fetched %d Departments", departments.size());
for (Department department : departments) {
assertEquals(3, department.getEmployees().size());
}
SELECT
d.id as id1_0_
FROM
Department d
-- Fetched 2 Departments
SELECT
e.department_id as departme3_1_0_,
e.id as id1_1_0_,
e.id as id1_1_1_,
e.department_id as departme3_1_1_,
e.username as username2_1_1_
FROM
Employee e
WHERE
e.department_id = 1
SELECT
e.department_id as departme3_1_0_,
e.id as id1_1_0_,
e.id as id1_1_1_,
e.department_id as departme3_1_1_,
e.username as username2_1_1_
FROM
Employee e
WHERE
e.department_id = 2
The more Department
entities are fetched by the first query, the more secondary SELECT
statements are executed to initialize the employees
collections.
Therefore, FetchMode.SELECT
can lead to N + 1 query issue.
11.11. FetchMode.SUBSELECT
To demonstrate how FetchMode.SUBSELECT
works, we are going to modify the FetchMode.SELECT
mapping example to use
FetchMode.SUBSELECT
:
Example 473. FetchMode.SUBSELECT
mapping example
@OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
@Fetch(FetchMode.SUBSELECT)
private List<Employee> employees = new ArrayList<>();
Now, we are going to fetch all Department
entities that match a given filtering predicate
and then navigate their employees
collections.
Hibernate is going to avoid the N + 1 query issue by generating a single SQL statement to initialize all employees
collections
for all Department
entities that were previously fetched.
Instead of passing all entity identifiers, Hibernate simply reruns the previous query that fetched the Department
entities.
Example 474. FetchMode.SUBSELECT
mapping example
List<Department> departments = entityManager.createQuery(
"select d " +
"from Department d " +
"where d.name like :token", Department.class)
.setParameter("token", "Department%")
.getResultList();
log.infof("Fetched %d Departments", departments.size());
for (Department department : departments) {
assertEquals(3, department.getEmployees().size());
}
SELECT
d.id as id1_0_
FROM
Department d
where
d.name like 'Department%'
-- Fetched 2 Departments
SELECT
e.department_id as departme3_1_1_,
e.id as id1_1_1_,
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.username as username2_1_0_
FROM
Employee e
WHERE
e.department_id in (
SELECT
fetchmodes0_.id
FROM
Department fetchmodes0_
WHERE
d.name like 'Department%'
)
11.12. FetchMode.JOIN
To demonstrate how FetchMode.JOIN
works, we are going to modify the FetchMode.SELECT
mapping example to use
FetchMode.JOIN
instead:
Example 475. FetchMode.JOIN
mapping example
@OneToMany(mappedBy = "department")
@Fetch(FetchMode.JOIN)
private List<Employee> employees = new ArrayList<>();
Now, we are going to fetch one Department
and navigate its employees
collections.
The reason why we are not using a JPQL query to fetch multiple To fetch multiple relationships with a JPQL query, the Therefore, Also, the |
Hibernate is going to avoid the secondary query by issuing an OUTER JOIN for the employees
collection.
Example 476. FetchMode.JOIN
mapping example
Department department = entityManager.find(Department.class, 1L);
log.infof("Fetched department: %s", department.getId());
assertEquals(3, department.getEmployees().size());
SELECT
d.id as id1_0_0_,
e.department_id as departme3_1_1_,
e.id as id1_1_1_,
e.id as id1_1_2_,
e.department_id as departme3_1_2_,
e.username as username2_1_2_
FROM
Department d
LEFT OUTER JOIN
Employee e
on d.id = e.department_id
WHERE
d.id = 1
-- Fetched department: 1
This time, there was no secondary query because the child collection was loaded along with the parent entity.
11.13. @LazyCollection
The @LazyCollection
annotation is used to specify the lazy fetching behavior of a given collection.
The possible values are given by the LazyCollectionOption
enumeration:
TRUE
-
Load it when the state is requested.
FALSE
-
Eagerly load it.
EXTRA
-
Prefer extra queries over full collection loading.
The TRUE
and FALSE
values are deprecated since you should be using the Jakarta Persistence FetchType
attribute of the [annotations-jpa-elementcollection], [annotations-jpa-onetomany], or [annotations-jpa-manytomany] collection.
The EXTRA
value has no equivalent in the Jakarta Persistence specification, and it’s used to avoid loading the entire collection even when the collection is accessed for the first time.
Each element is fetched individually using a secondary query.
Example 477. LazyCollectionOption.EXTRA
mapping example
@Entity(name = "Department")
public static class Department {
@Id
private Long id;
@OneToMany(mappedBy = "department", cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
@LazyCollection(LazyCollectionOption.EXTRA)
private List<Employee> employees = new ArrayList<>();
//Getters and setters omitted for brevity
}
@Entity(name = "Employee")
public static class Employee {
@Id
private Long id;
@NaturalId
private String username;
@ManyToOne(fetch = FetchType.LAZY)
private Department department;
//Getters and setters omitted for brevity
}
For bags (e.g. regular List(s) of entities that do not preserve any certain ordering), |
Now, considering we have the following entities:
Example 478. LazyCollectionOption.EXTRA
Domain Model example
Department department = new Department();
department.setId(1L);
entityManager.persist(department);
for (long i = 1; i <= 3; i++) {
Employee employee = new Employee();
employee.setId(i);
employee.setUsername(String.format("user_%d", i));
department.addEmployee(employee);
}
When fetching the employee
collection entries by their position in the List
,
Hibernate generates the following SQL statements:
Example 479. LazyCollectionOption.EXTRA
fetching example
Department department = entityManager.find(Department.class, 1L);
int employeeCount = department.getEmployees().size();
for(int i = 0; i < employeeCount; i++) {
log.infof("Fetched employee: %s", department.getEmployees().get(i).getUsername());
}
SELECT
max(order_id) + 1
FROM
Employee
WHERE
department_id = ?
-- binding parameter [1] as [BIGINT] - [1]
SELECT
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.username as username2_1_0_
FROM
Employee e
WHERE
e.department_id=?
AND e.order_id=?
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [INTEGER] - [0]
SELECT
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.username as username2_1_0_
FROM
Employee e
WHERE
e.department_id=?
AND e.order_id=?
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [INTEGER] - [1]
SELECT
e.id as id1_1_0_,
e.department_id as departme3_1_0_,
e.username as username2_1_0_
FROM
Employee e
WHERE
e.department_id=?
AND e.order_id=?
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [INTEGER] - [2]
Therefore, the child entities were fetched one after the other without triggering a full collection initialization. For this reason, caution is advised since accessing all elements using |
12. Batching
12.1. JDBC batching
JDBC offers support for batching together SQL statements that can be represented as a single PreparedStatement.
Implementation wise this generally means that drivers will send the batched operation to the server in one call,
which can save on network calls to the database. Hibernate can leverage JDBC batching.
The following settings control this behavior.
hibernate.jdbc.batch_size
-
Controls the maximum number of statements Hibernate will batch together before asking the driver to execute the batch.
Zero or a negative number disables this feature. hibernate.jdbc.batch_versioned_data
-
Some JDBC drivers return incorrect row counts when a batch is executed.
If your JDBC driver falls into this category this setting should be set tofalse
.
Otherwise, it is safe to enable this which will allow Hibernate to still batch the DML for versioned entities and still use the returned row counts for optimistic lock checks.
Since 5.0, it defaults to true. Previously (versions 3.x and 4.x), it used to be false. hibernate.jdbc.batch.builder
-
Names the implementation class used to manage batching capabilities.
It is almost never a good idea to switch from Hibernate’s default implementation.
But if you wish to, this setting would name theorg.hibernate.engine.jdbc.batch.spi.BatchBuilder
implementation to use. hibernate.order_updates
-
Forces Hibernate to order SQL updates by the entity type and the primary key value of the items being updated.
This allows for more batching to be used. It will also result in fewer transaction deadlocks in highly concurrent systems.
Comes with a performance hit, so benchmark before and after to see if this actually helps or hurts your application. hibernate.order_inserts
-
Forces Hibernate to order inserts to allow for more batching to be used.
Comes with a performance hit, so benchmark before and after to see if this actually helps or hurts your application.
Since version 5.2, Hibernate allows overriding the global JDBC batch size given by the |
Example 480. Hibernate specific JDBC batch size configuration on a per Session
basis
entityManager
.unwrap(Session.class)
.setJdbcBatchSize(10);
12.2. Session batching
The following example shows an anti-pattern for batch inserts.
Example 481. Naive way to insert 100 000 entities with Hibernate
EntityManager entityManager = null;
EntityTransaction txn = null;
try {
entityManager = entityManagerFactory().createEntityManager();
txn = entityManager.getTransaction();
txn.begin();
for (int i = 0; i < 100_000; i++) {
Person Person = new Person(String.format("Person %d", i));
entityManager.persist(Person);
}
txn.commit();
} catch (RuntimeException e) {
if (txn != null && txn.isActive()) txn.rollback();
throw e;
} finally {
if (entityManager != null) {
entityManager.close();
}
}
There are several problems associated with this example:
-
Hibernate caches all the newly inserted
Person
instances in the session-level cache, so, when the transaction ends, 100 000 entities are managed by the persistence context.
If the maximum memory allocated to the JVM is rather low, this example could fail with anOutOfMemoryException
.
The Java 1.8 JVM allocated either 1/4 of available RAM or 1Gb, which can easily accommodate 100 000 objects on the heap. -
long-running transactions can deplete a connection pool so other transactions don’t get a chance to proceed.
-
JDBC batching is not enabled by default, so every insert statement requires a database roundtrip.
To enable JDBC batching, set thehibernate.jdbc.batch_size
property to an integer between 10 and 50.
Hibernate disables insert batching at the JDBC level transparently if you use an identity identifier generator. |
12.2.1. Batch inserts
When you make new objects persistent, employ methods flush()
and clear()
to the session regularly, to control the size of the first-level cache.
Example 482. Flushing and clearing the Session
EntityManager entityManager = null;
EntityTransaction txn = null;
try {
entityManager = entityManagerFactory().createEntityManager();
txn = entityManager.getTransaction();
txn.begin();
int batchSize = 25;
for (int i = 0; i < entityCount; i++) {
if (i > 0 && i % batchSize == 0) {
//flush a batch of inserts and release memory
entityManager.flush();
entityManager.clear();
}
Person Person = new Person(String.format("Person %d", i));
entityManager.persist(Person);
}
txn.commit();
} catch (RuntimeException e) {
if (txn != null && txn.isActive()) txn.rollback();
throw e;
} finally {
if (entityManager != null) {
entityManager.close();
}
}
12.2.2. Session scroll
When you retrieve and update data, flush()
and clear()
the session regularly.
In addition, use method scroll()
to take advantage of server-side cursors for queries that return many rows of data.
If left unclosed by the application, Hibernate will automatically close the underlying resources (e.g. However, it is good practice to close the |
12.2.3. StatelessSession
StatelessSession
is an alternative to Session
and provides:
-
a command-oriented API
-
with no associated persistence context.
Thus, a stateless session is a slightly lower-level abstraction that’s closer to the underlying JDBC activity:
-
there’s no first-level cache,
-
the stateless session does not interact with any second-level or query cache, and
-
there’s no transactional write-behind or automatic dirty checking.
Instead, persistence operations occur synchronously when a method of StatelessSession
is invoked, and entities returned by a stateless session are always detached.
A stateless session may be used to stream data to and from the database in the form of detached objects. |
The StatelessSession
API comes with certain limitations:
-
operations performed using a stateless session never cascade to associated instances,
-
collections are ignored by a stateless session,
-
lazy loading of associations is not transparent, and is only available via an explicit operation named
fetch()
, and -
operations performed via a stateless session bypass Hibernate’s event model and interceptors.
Due to the lack of a first-level cache, stateless sessions are vulnerable to data aliasing effects. |
Example 484. Using a StatelessSession
StatelessSession statelessSession = null;
Transaction txn = null;
ScrollableResults scrollableResults = null;
try {
SessionFactory sessionFactory = entityManagerFactory().unwrap(SessionFactory.class);
statelessSession = sessionFactory.openStatelessSession();
txn = statelessSession.getTransaction();
txn.begin();
scrollableResults = statelessSession
.createSelectionQuery("select p from Person p")
.scroll(ScrollMode.FORWARD_ONLY);
while (scrollableResults.next()) {
Person Person = (Person) scrollableResults.get();
processPerson(Person);
statelessSession.update(Person);
}
txn.commit();
} catch (RuntimeException e) {
if (txn != null && txn.getStatus() == TransactionStatus.ACTIVE) txn.rollback();
throw e;
} finally {
if (scrollableResults != null) {
scrollableResults.close();
}
if (statelessSession != null) {
statelessSession.close();
}
}
The Person
instances returned by the query are immediately detached.
They are never associated with any persistence context.
The |
12.3. Hibernate Query Language for DML
DML, or Data Manipulation Language, refers to SQL statements such as INSERT
, UPDATE
, and DELETE
.
Hibernate provides methods for bulk SQL-style DML statement execution, in the form of Hibernate Query Language (HQL).
12.3.1. HQL/JPQL for UPDATE and DELETE
Both the Hibernate native Query Language and JPQL (Java Persistence Query Language) provide support for bulk UPDATE and DELETE.
Example 485. Pseudo-syntax for UPDATE and DELETE statements using HQL
UPDATE FROM EntityName e WHERE e.name = ?
DELETE FROM EntityName e WHERE e.name = ?
Although the |
The FROM
clause can only refer to a single entity, which can be aliased.
If the entity name is aliased, any property references must be qualified using that alias.
If the entity name is not aliased, then it is illegal for any property references to be qualified.
Joins, either implicit or explicit, are prohibited in a bulk HQL query. |
Example 486. Executing a JPQL UPDATE
, using the Query.executeUpdate()
int updatedEntities = entityManager.createQuery(
"update Person p " +
"set p.name = :newName " +
"where p.name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
Example 487. Executing an HQL UPDATE
, using the Query.executeUpdate()
int updatedEntities = session.createMutationQuery(
"update Person " +
"set name = :newName " +
"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
In keeping with the EJB3 specification, HQL UPDATE
statements, by default, do not effect the version or the timestamp property values for the affected entities.
You can use a versioned update to force Hibernate to reset the version or timestamp property values, by adding the VERSIONED
keyword after the UPDATE
keyword.
Example 488. Updating the version of timestamp
int updatedEntities = session.createMutationQuery(
"update versioned Person " +
"set name = :newName " +
"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
If you use the This feature is only available in HQL since it’s not standardized by Jakarta Persistence. |
Example 489. A JPQL DELETE
statement
int deletedEntities = entityManager.createQuery(
"delete Person p " +
"where p.name = :name")
.setParameter("name", name)
.executeUpdate();
Example 490. An HQL DELETE
statement
int deletedEntities = session.createMutationQuery(
"delete Person " +
"where name = :name")
.setParameter("name", name)
.executeUpdate();
Method Query.executeUpdate()
returns an int
value, which indicates the number of entities affected by the operation.
This may or may not correlate to the number of rows affected in the database.
A JPQL/HQL bulk operation might result in multiple SQL statements being executed, such as for joined-subclass.
In the example of joined-subclass, a DELETE
against one of the subclasses may actually result in deletes in the tables underlying the join, or further down the inheritance hierarchy.
12.3.2. HQL syntax for INSERT
Example 491. Pseudo-syntax for INSERT-SELECT statements
INSERT INTO EntityName
properties_list
SELECT select_list
FROM ...
Alternatively one can also declare individual values
Example 492. Pseudo-syntax for INSERT-VALUES statements
INSERT INTO EntityName
properties_list
VALUES values_list
The properties_list
is analogous to the column specification in the SQL
INSERT
statement.
Note that INSERT
statements are inherently non-polymorphic, so it is not possible to use an EntityName
which is abstract or refer to subclass properties.
The SELECT statement can be any valid HQL select query, but the return types must match the types expected by the INSERT.
Hibernate verifies the return types during query compilation, instead of expecting the database to check it.
Problems might result from Hibernate types which are equivalent, rather than equal.
One such example is a mismatch between a property defined as an org.hibernate.type.StandardBasicTypes.DATE
and a property defined as an org.hibernate.type.StandardBasicTypes.TIMESTAMP
,
even though the database may not make a distinction, or may be capable of handling the conversion.
If id property is not specified in the properties_list
, Hibernate generates a value automatically.
Automatic generation is only available if you use ID generators which operate on the database.
Otherwise, Hibernate throws an exception during parsing. Available in-database generators implement
org.hibernate.id.PostInsertIdentifierGenerator
.
For properties mapped as either version or timestamp, the insert statement gives you two options.
You can either specify the property in the properties_list, in which case its value is taken from the corresponding select expressions or omit it from the properties_list,
in which case the seed value defined by the org.hibernate.type.descriptor.java.VersionJavaType
is used.
Example 493. HQL INSERT statement
int insertedEntities = session.createMutationQuery(
"insert into Partner (id, name) " +
"select p.id, p.name " +
"from Person p ")
.executeUpdate();
This section is only a brief overview of HQL. For more information, see Hibernate Query Language.
12.3.3. Bulk mutation strategies
When a bulk mutation involves multiple tables, Hibernate has to issue individual DML statements to the respective tables.
Since the mutation itself could have an effect on the conditions used in the statement, it’s generally not possible
to simply execute parts of the DML statement against the respective tables. Instead, Hibernate has to temporarily remember
which rows will be affected, and execute the DML statements based on these rows.
Usually, Hibernate will make use of local or global temporary tables to remember the primary keys of the rows.
For some databases, currently only PostgreSQL and DB2, a more advanced strategy (CteMutationStrategy
) is used,
which makes use of DML in CTE support to execute the whole operation in one SQL statement.
The chosen strategy, unless overridden through the hibernate.query.mutation_strategy
setting, is based on the
Dialect support through org.hibernate.dialect.Dialect.getFallbackSqmMutationStrategy
.
Class diagram
Considering we have the following entities:
The Person
entity is the base class of this entity inheritance model, and is mapped as follows:
Example 494. Bulk mutation base class entity
@Entity(name = "Person")
@Inheritance(strategy = InheritanceType.JOINED)
public static class Person implements Serializable {
@Id
private Integer id;
@Id
private String companyName;
private String name;
private boolean employed;
//Getters and setters are omitted for brevity
}
Both the Doctor
and Engineer
entity classes extend the Person
base class:
Example 495. Bulk mutation subclass entities
@Entity(name = "Doctor")
public static class Doctor extends Person {
}
@Entity(name = "Engineer")
public static class Engineer extends Person {
private boolean fellow;
public boolean isFellow() {
return fellow;
}
public void setFellow(boolean fellow) {
this.fellow = fellow;
}
}
Inheritance tree bulk processing
Now, when you try to execute a bulk entity delete query:
Example 496. Bulk mutation delete query example
int updateCount = session.createQuery(
"delete from Person where employed = :employed" )
.setParameter( "employed", false )
.executeUpdate();
create temporary table
HT_Person
(
id int4 not null,
companyName varchar(255) not null
)
insert
into
HT_Person
select
p.id as id,
p.companyName as companyName
from
Person p
where
p.employed = ?
delete
from
Engineer
where
(
id, companyName
) IN (
select
id,
companyName
from
HT_Person
)
delete
from
Doctor
where
(
id, companyName
) IN (
select
id,
companyName
from
HT_Person
)
delete
from
Person
where
(
id, companyName
) IN (
select
id,
companyName
from
HT_Person
)
HT_Person
is a temporary table that Hibernate creates to hold all the entity identifiers that are to be updated or deleted by the bulk operation.
The temporary table can be either global or local, depending on the underlying database capabilities.
Non-temporary table bulk mutation strategies
When the temporary table strategy can not be used because the database user lacks privilege to create temporary tables,
the InlineMutationStrategy
must be used.
To use this strategy, you need to configure the following configuration property:
<property name="hibernate.query.mutation_strategy"
value="org.hibernate.query.sqm.mutation.internal.inline.InlineMutationStrategy"
/>
Now, when running the previous test case, Hibernate generates the following SQL statements:
Example 497. InlineIdsInClauseBulkIdStrategy
delete entity query example
select
p.id as id,
p.companyName as companyName
from
Person p
where
p.employed = ?
delete
from
Engineer
where
( id, companyName )
in (
( 1,'Red Hat USA' ),
( 3,'Red Hat USA' ),
( 1,'Red Hat Europe' ),
( 3,'Red Hat Europe' )
)
delete
from
Doctor
where
( id, companyName )
in (
( 1,'Red Hat USA' ),
( 3,'Red Hat USA' ),
( 1,'Red Hat Europe' ),
( 3,'Red Hat Europe' )
)
delete
from
Person
where
( id, companyName )
in (
( 1,'Red Hat USA' ),
( 3,'Red Hat USA' ),
( 1,'Red Hat Europe' ),
( 3,'Red Hat Europe' )
)
So, the entity identifiers are selected first and used for each particular update or delete statement.
13. Caching
At runtime, Hibernate handles moving data into and out of the second-level cache in response to the operations performed by the Session
, which acts as a transaction-level cache of persistent data.
Once an entity becomes managed, that object is added to the internal cache of the current persistence context (EntityManager
or Session
).
The persistence context is also called the first-level cache, and it’s enabled by default.
It is possible to configure a JVM-level (SessionFactory
-level) or even a cluster cache on a class-by-class and collection-by-collection basis.
Be aware that Hibernate caches are not aware of changes made to the persistent store by other applications. To address this limitation, you can configure a TTL (Time To Live) retention policy at the second-level cache region level so that the underlying cache entries expire regularly. |
13.1. Configuring second-level caching
Hibernate can integrate with various caching providers for the purpose of caching data outside the context of a particular Session
.
This section defines the settings which control this behavior.
13.1.1. RegionFactory
org.hibernate.cache.spi.RegionFactory
defines the integration between Hibernate and a pluggable caching provider.
hibernate.cache.region.factory_class
is used to declare the provider to use.
Hibernate comes with built-in support for the Java caching standard JCache
and also the popular caching library: Infinispan.
Detailed information is provided later in this chapter.
13.1.2. Caching configuration properties
Besides provider specific configuration, there are a number of configurations options on the Hibernate side of the integration that control various caching behaviors:
hibernate.cache.use_second_level_cache
-
Enable or disable second level caching overall. By default, if the currently configured
RegionFactory
is not theNoCachingRegionFactory
, then the second-level cache is going to be enabled. Otherwise, the second-level cache is disabled. hibernate.cache.use_query_cache
-
Enable or disable second level caching of query results. The default is false.
hibernate.cache.query_cache_factory
-
Query result caching is handled by a special contract that deals with staleness-based invalidation of the results.
The default implementation does not allow stale results at all. Use this for applications that would like to relax that.
Names an implementation oforg.hibernate.cache.spi.TimestampsCacheFactory
. hibernate.cache.use_minimal_puts
-
Optimizes second-level cache operations to minimize writes, at the cost of more frequent reads. Providers typically set this appropriately.
hibernate.cache.region_prefix
-
Defines a name to be used as a prefix to all second-level cache region names.
hibernate.cache.default_cache_concurrency_strategy
-
In Hibernate second-level caching, all regions can be configured differently including the concurrency strategy to use when accessing that particular region.
This setting allows defining a default strategy to be used.
This setting is very rarely required as the pluggable providers do specify the default strategy to use.
Valid values include:-
read-only,
-
read-write,
-
nonstrict-read-write,
-
transactional
-
hibernate.cache.use_structured_entries
-
If
true
, forces Hibernate to store data in the second-level cache in a more human-friendly format.
Can be useful if you’d like to be able to «browse» the data directly in your cache, but does have a performance impact. hibernate.cache.auto_evict_collection_cache
-
Enables or disables the automatic eviction of a bidirectional association’s collection cache entry when the association is changed just from the owning side.
This is disabled by default, as it has a performance impact to track this state.
However, if your application does not manage both sides of bidirectional association where the collection side is cached,
the alternative is to have stale data in that collection cache. hibernate.cache.use_reference_entries
-
Enable direct storage of entity references into the second level cache for read-only or immutable entities.
hibernate.cache.keys_factory
-
When storing entries into the second-level cache as a key-value pair, the identifiers can be wrapped into tuples
<entity type, tenant, identifier> to guarantee uniqueness in case that second-level cache stores all entities
in single space. These tuples are then used as keys in the cache. When the second-level cache implementation
(incl. its configuration) guarantees that different entity types are stored separately and multi-tenancy is not
used, you can omit this wrapping to achieve better performance. Currently, this property is only supported when
Infinispan is configured as the second-level cache implementation. Valid values are:-
default
(wraps identifiers in the tuple) -
simple
(uses identifiers as keys without any wrapping) -
fully qualified class name that implements
org.hibernate.cache.spi.CacheKeysFactory
-
13.2. Configuring second-level cache mappings
The cache mappings can be configured via Jakarta Persistence annotations or XML descriptors or using the Hibernate-specific mapping files.
By default, entities are not part of the second level cache and we recommend you to stick to this setting.
However, you can override this by setting the shared-cache-mode
element in your persistence.xml
file
or by using the jakarta.persistence.sharedCache.mode
property in your configuration file.
The following values are possible:
ENABLE_SELECTIVE
(Default and recommended value)-
Entities are not cached unless explicitly marked as cacheable (with the
@Cacheable
annotation). DISABLE_SELECTIVE
-
Entities are cached unless explicitly marked as non-cacheable.
ALL
-
Entities are always cached even if marked as non-cacheable.
NONE
-
No entity is cached even if marked as cacheable.
This option can make sense to disable second-level cache altogether.
The cache concurrency strategy used by default can be set globally via the hibernate.cache.default_cache_concurrency_strategy
configuration property.
The values for this property are:
- read-only
-
If your application needs to read, but not modify, instances of a persistent class, a read-only cache is the best choice.
Application can still delete entities and these changes should be reflected in second-level cache so that the cache
does not provide stale entities.
Implementations may use performance optimizations based on the immutability of entities. - read-write
-
If the application needs to update data, a read-write cache might be appropriate.
This strategy provides consistent access to single entity, but not a serializable transaction isolation level; e.g. when TX1 reads looks up an entity and does not find it, TX2 inserts the entity into cache and TX1 looks it up again, the new entity can be read in TX1. - nonstrict-read-write
-
Similar to read-write strategy but there might be occasional stale reads upon concurrent access to an entity. The choice of this strategy might be appropriate if the application rarely updates the same data simultaneously and strict transaction isolation is not required. Implementations may use performance optimizations that make use of the relaxed consistency guarantee.
- transactional
-
Provides serializable transaction isolation level.
Rather than using a global setting, it is recommended to define the cache concurrency strategy on a per entity basis. |
The @Cache
annotation define three attributes:
- usage
-
Defines the
CacheConcurrencyStrategy
- region
-
Defines a cache region where entries will be stored
- include
-
If lazy properties should be included in the second level cache.
The default value isall
so lazy properties are cacheable.
The other possible value isnon-lazy
so lazy properties are not cacheable.
13.3. Entity inheritance and second-level cache mapping
Traditionally, when using entity inheritance, Hibernate required an entity hierarchy to be either cached entirely or not cached at all.
Therefore, if you wanted to cache a subclass belonging to a given entity hierarchy,
the Jakarta Persistence @Cacheable
and the Hibernate-specific @Cache
annotations would have to be declared at the root-entity level only.
Although we still believe that all entities belonging to a given entity hierarchy should share the same caching semantics,
the Jakarta Persistence specification says that the @Cacheable
annotation could be overwritten by a subclass:
The value of the
Cacheable
annotation is inherited by subclasses; it can be overridden by specifyingCacheable
on a subclass.
— Section 11.1.7 of the Jakarta Persistence
As of Hibernate ORM 5.3, you can now override a base class However, the Hibernate cache concurrency strategy (e.g. read-only, nonstrict-read-write, read-write, transactional) is still defined at the root entity level and cannot be overridden. |
Nevertheless, the reasons why we advise you to have all entities belonging to an inheritance tree share the same caching definition can be summed as follows:
-
from a performance perspective, adding an additional check on a per entity type level slows the bootstrap process.
-
providing different caching semantics for subclasses would violate the Liskov substitution principle.
13.4. Entity cache
Example 498. Entity cache mapping
@Entity(name = "Phone")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public static class Phone {
@Id
@GeneratedValue
private Long id;
private String mobile;
@ManyToOne
private Person person;
@Version
private int version;
//Getters and setters are omitted for brevity
}
Hibernate stores cached entities in a dehydrated form, which is similar to the database representation.
Aside from the foreign key column values of the @ManyToOne
or @OneToOne
child-side associations,
entity relationships are not stored in the cache,
Once an entity is stored in the second-level cache, you can avoid a database hit and load the entity from the cache alone:
Example 499. Loading entity using Jakarta Persistence
Person person = entityManager.find(Person.class, 1L);
Example 500. Loading entity using Hibernate native API
Person person = session.get(Person.class, 1L);
The Hibernate second-level cache can also load entities by their natural id:
Example 501. Hibernate natural id entity mapping
@Entity(name = "Person")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public static class Person {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name;
@NaturalId
@Column(name = "code", unique = true)
private String code;
//Getters and setters are omitted for brevity
}
Example 502. Loading entity using Hibernate native natural id API
Person person = session
.byNaturalId(Person.class)
.using("code", "unique-code")
.load();
13.5. Collection cache
Hibernate can also cache collections, and the @Cache
annotation must be on added to the collection property.
If the collection is made of value types (basic or embeddables mapped with @ElementCollection
),
the collection is stored as such.
If the collection contains other entities (@OneToMany
or @ManyToMany
),
the collection cache entry will store the entity identifiers only.
Example 503. Collection cache mapping
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
private List<Phone> phones = new ArrayList<>();
Collections are read-through, meaning they are cached upon being accessed for the first time:
Example 504. Collection cache usage
Person person = entityManager.find(Person.class, 1L);
person.getPhones().size();
Subsequent collection retrievals will use the cache instead of going to the database.
The collection cache is not write-through so any modification will trigger a collection cache entry invalidation. |
13.6. Query cache
Aside from caching entities and collections, Hibernate offers a query cache too.
This is useful for frequently executed queries with fixed parameter values.
Caching of query results introduces some overhead in terms of your applications normal transactional processing. That, coupled with the fact that most applications simply gain no benefit from caching query results, |
To use query caching, you will first need to enable it with the following configuration property:
Example 505. Enabling query cache
<property
name="hibernate.cache.use_query_cache"
value="true" />
As mentioned above, most queries do not benefit from caching or their results.
So by default, individual queries are not cached even after enabling query caching.
Each particular query that needs to be cached must be manually set as cacheable.
This way, the query looks for existing cache results or adds the query results to the cache when being executed.
Example 506. Caching query using Jakarta Persistence
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name = :name", Person.class)
.setParameter("name", "John Doe")
.setHint("org.hibernate.cacheable", "true")
.getResultList();
Example 507. Caching query using Hibernate native API
List<Person> persons = session.createQuery(
"select p " +
"from Person p " +
"where p.name = :name", Person.class)
.setParameter("name", "John Doe")
.setCacheable(true)
.list();
For entity queries, the query cache does not cache the state of the actual entities. Instead, it stores the entity identifiers, and when the query result is fetched from the cache, the entity state is going to be loaded from the second-level cache entity regions. Just as with collection caching, the query cache should always be used in conjunction with the second-level cache for those entities expected to be cached as part of a query result cache. For projection queries, the query cache stores the dehydrated entity state (e.g. |
13.6.1. Query cache regions
This setting creates two new cache regions:
default-query-results-region
-
Holding the cached query results.
default-update-timestamps-region
-
Holding timestamps of the most recent updates to queryable tables.
These are used to validate the results as they are served from the query cache.
If you configure your underlying cache implementation to use expiration, it’s very important In fact, we recommend that the |
If you require fine-grained control over query cache expiration policies,
you can specify a named cache region for a particular query.
Example 508. Caching query in custom region using Jakarta Persistence
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setHint(HINT_CACHEABLE, "true")
.setHint(HINT_CACHE_REGION, "query.cache.person")
.getResultList();
Example 509. Caching query in custom region using Hibernate native API
List<Person> persons = session.createQuery(
"select p " +
"from Person p " +
"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setCacheable(true)
.setCacheRegion("query.cache.person")
.list();
If you want to force the query cache to refresh one of its regions (disregarding any cached results it finds there),
you can use custom cache modes.
Example 510. Using custom query cache mode with Jakarta Persistence
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setHint(HINT_CACHEABLE, "true")
.setHint(HINT_CACHE_REGION, "query.cache.person")
.setHint("jakarta.persistence.cache.storeMode", CacheStoreMode.REFRESH)
.getResultList();
Example 511. Using custom query cache mode with Hibernate native API
List<Person> persons = session.createQuery(
"select p " +
"from Person p " +
"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setCacheable(true)
.setCacheRegion("query.cache.person")
.setCacheMode(CacheMode.REFRESH)
.list();
When using This behavior is particularly useful in cases when the underlying data may have been updated via a separate process
|
13.7. Managing the cached data
Traditionally, Hibernate defined the CacheMode
enumeration to describe
the ways of interactions with the cached data.
Jakarta Persistence split cache modes by storage (CacheStoreMode
)
and retrieval (CacheRetrieveMode
).
The relationship between Hibernate and Jakarta Persistence cache modes can be seen in the following table:
Hibernate | Jakarta Persistence | Description |
---|---|---|
|
|
Default. Reads/writes data from/into the cache |
|
|
Doesn’t read from cache, but writes to the cache upon loading from the database |
|
|
Doesn’t read from cache, but writes to the cache as it reads from the database |
|
|
Read from the cache, but doesn’t write to cache |
|
|
Doesn’t read/write data from/into the cache |
Setting the cache mode can be done either when loading entities directly or when executing a query.
Example 512. Using custom cache modes with Jakarta Persistence
Map<String, Object> hints = new HashMap<>();
hints.put("jakarta.persistence.cache.retrieveMode" , CacheRetrieveMode.USE);
hints.put("jakarta.persistence.cache.storeMode" , CacheStoreMode.REFRESH);
Person person = entityManager.find(Person.class, 1L , hints);
Example 513. Using custom cache modes with Hibernate native API
session.setCacheMode(CacheMode.REFRESH);
Person person = session.get(Person.class, 1L);
The custom cache modes can be set for queries as well:
Example 514. Using custom cache modes for queries with Jakarta Persistence
List<Person> persons = entityManager.createQuery(
"select p from Person p", Person.class)
.setHint(HINT_CACHEABLE, "true")
.setHint("jakarta.persistence.cache.retrieveMode" , CacheRetrieveMode.USE)
.setHint("jakarta.persistence.cache.storeMode" , CacheStoreMode.REFRESH)
.getResultList();
Example 515. Using custom cache modes for queries with Hibernate native API
List<Person> persons = session.createQuery(
"select p from Person p", Person.class)
.setCacheable(true)
.setCacheMode(CacheMode.REFRESH)
.list();
13.7.1. Evicting cache entries
Because the second level cache is bound to the EntityManagerFactory
or the SessionFactory
,
cache eviction must be done through these two interfaces.
Example 516. Evicting entities with Jakarta Persistence
entityManager.getEntityManagerFactory().getCache().evict(Person.class);
Hibernate is much more flexible in this regard as it offers fine-grained control over what needs to be evicted.
The org.hibernate.Cache
interface defines various evicting strategies:
-
entities (by their class or region)
-
entities stored using the natural-id (by their class or region)
-
collections (by the region, and it might take the collection owner identifier as well)
-
queries (by region)
Example 517. Evicting entities with Hibernate native API
session.getSessionFactory().getCache().evictQueryRegion("query.cache.person");
13.8. Caching statistics
If you enable the hibernate.generate_statistics
configuration property,
Hibernate will expose a number of metrics via SessionFactory.getStatistics()
.
Hibernate can even be configured to expose these statistics via JMX.
This way, you can get access to the Statistics
class which comprises all sort of
second-level cache metrics.
Example 518. Caching statistics
Statistics statistics = session.getSessionFactory().getStatistics();
CacheRegionStatistics secondLevelCacheStatistics =
statistics.getDomainDataRegionStatistics("query.cache.person");
long hitCount = secondLevelCacheStatistics.getHitCount();
long missCount = secondLevelCacheStatistics.getMissCount();
double hitRatio = (double) hitCount / (hitCount + missCount);
13.9. JCache
To use the built-in integration for JCache, you need the In addition, a JCache implementation needs to be added as well. |
13.9.1. RegionFactory
The hibernate-jcache
module defines the following region factory: JCacheRegionFactory
.
To use the JCacheRegionFactory
, you need to specify the following configuration property:
Example 519. JCacheRegionFactory
configuration
<property
name="hibernate.cache.region.factory_class"
value="jcache"/>
The JCacheRegionFactory
configures a javax.cache.CacheManager
.
13.9.2. JCache CacheManager
JCache mandates that CacheManager
s sharing the same URI and class loader be unique in JVM.
If you do not specify additional properties, the JCacheRegionFactory
will load the default JCache provider and create the default CacheManager
.
Also, Cache
s will be created using the default javax.cache.configuration.MutableConfiguration
.
In order to control which provider to use and specify configuration for the CacheManager
and Cache
s you can use the following two properties:
Example 520. JCache configuration
<property
name="hibernate.javax.cache.provider"
value="org.ehcache.jsr107.EhcacheCachingProvider"/>
<property
name="hibernate.javax.cache.uri"
value="file:/path/to/ehcache.xml"/>
Only by specifying the second property hibernate.javax.cache.uri
will you be able to have a CacheManager
per SessionFactory
.
Using a non-default JCache CacheManager
If you don’t want to use the default CacheManager
, you need to set the hibernate.javax.cache.cache_manager
configuration property
to one of the following values:
- Object reference
-
If the value is an
Object
instance implementing theCacheManager
interface,
the providedCacheManager
instance will be used. Class
-
If the value is a Java
Class
object that implements theCacheManager
interface,
Hibernate will create a new instance for thatClass
and use it instead of the default one.When passing a Java
Class
that implements theCacheManager
interface, you must make sure that theCacheManager
implementation class provides a default no-arg constructor because that’s going to be used to instantiate aCacheManager
implementationObject
. String
-
If the value is a Java
String
, Hibernate expects it to be the fully-qualifiedClass
name
of theCacheManager
implementation which will be used to instantiate the non-defaultCacheManager
.When passing the fully-qualified class name, you must make sure that the associated
Class
type provides a default no-arg constructor because that’s going to be used to instantiate aCacheManager
implementationObject
.
13.9.3. JCache missing cache strategy
By default, the JCache region factory
will log a warning when asked to create a cache that is not explicitly configured and pre-started in the underlying cache manager.
Thus if you configure an entity type or a collection as cached, but do not configure the corresponding cache explicitly,
one warning will be logged for each cache that was not configured explicitly.
You may change this behavior by setting the hibernate.javax.cache.missing_cache_strategy
property
to one of the following values:
Value | Description |
---|---|
|
Fail with an exception on missing caches. |
|
Default value. Create a new cache when a cache is not found (see |
|
Create a new cache when a cache is not found, without logging any warning about the missing cache. |
Note that caches created this way may not be suitable for production usage (unlimited size and no eviction in particular) unless the cache provider explicitly provides a specific configuration for default caches. Recent versions of Ehcache enable disk persistence ( Ehcache, in particular, allows to set such default configuration using cache templates. See the Ehcache documentation for more details. |
13.10. Infinispan
Infinispan is a distributed in-memory key/value data store, available as a cache or data grid, which can be used as a Hibernate second-level cache provider as well.
It supports advanced functionality such as transactions, events, querying, distributed processing, off-heap and geographical failover.
14. Interceptors and Events
It is useful for the application to react to certain events that occur inside Hibernate.
This allows for the implementation of generic functionality and the extension of Hibernate functionality.
14.1. Interceptors
The org.hibernate.Interceptor
interface provides callbacks from the session to the application,
allowing the application to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted or loaded.
One possible use for this is to track auditing information.
The following example shows an Interceptor
implementation that automatically logs when an entity is updated.
public static class LoggingInterceptor implements Interceptor {
@Override
public boolean onFlushDirty(
Object entity,
Object id,
Object[] currentState,
Object[] previousState,
String[] propertyNames,
Type[] types) {
LOGGER.debugv("Entity {0}#{1} changed from {2} to {3}",
entity.getClass().getSimpleName(),
id,
Arrays.toString(previousState),
Arrays.toString(currentState)
);
return Interceptor.super.onFlushDirty(entity, id, currentState,
previousState, propertyNames, types
);
}
}
You can either implement |
An Interceptor can be either Session
-scoped or SessionFactory
-scoped.
A Session-scoped interceptor is specified when a session is opened.
SessionFactory sessionFactory = entityManagerFactory.unwrap(SessionFactory.class);
Session session = sessionFactory
.withOptions()
.interceptor(new LoggingInterceptor())
.openSession();
session.getTransaction().begin();
Customer customer = session.get(Customer.class, customerId);
customer.setName("Mr. John Doe");
//Entity Customer#1 changed from [John Doe, 0] to [Mr. John Doe, 0]
session.getTransaction().commit();
A SessionFactory
-scoped interceptor is registered with the Configuration
object prior to building the SessionFactory
.
Unless a session is opened explicitly specifying the interceptor to use, the SessionFactory
-scoped interceptor will be applied to all sessions opened from that SessionFactory
.
SessionFactory
-scoped interceptors must be thread-safe.
Ensure that you do not store session-specific states since multiple sessions will use this interceptor potentially concurrently.
SessionFactory sessionFactory = new MetadataSources(new StandardServiceRegistryBuilder().build())
.addAnnotatedClass(Customer.class)
.getMetadataBuilder()
.build()
.getSessionFactoryBuilder()
.applyInterceptor(new LoggingInterceptor())
.build();
14.2. Native Event system
If you have to react to particular events in the persistence layer, you can also use the Hibernate event architecture.
The event system can be used in place of or in addition to interceptors.
Many methods of the Session
interface correlate to an event type.
The full range of defined event types is declared as enum values on org.hibernate.event.spi.EventType
.
When a request is made of one of these methods, the Session generates an appropriate event and passes it to the configured event listener(s) for that type.
Applications can customize the listener interfaces (i.e., the LoadEvent
is processed by the registered implementation of the LoadEventListener
interface), in which case their implementations would
be responsible for processing the load()
requests made of the Session
.
The listeners should be considered stateless. They are shared between requests, and should not save any state as instance variables. |
A custom listener implements the appropriate interface for the event it wants to process and/or extend one of the convenience base classes
(or even the default event listeners used by Hibernate out-of-the-box as these are declared non-final for this purpose).
Here is an example of a custom load event listener:
Example 521. Custom LoadListener
example
EntityManagerFactory entityManagerFactory = entityManagerFactory();
SessionFactoryImplementor sessionFactory = entityManagerFactory.unwrap( SessionFactoryImplementor.class );
sessionFactory
.getServiceRegistry()
.getService( EventListenerRegistry.class )
.prependListeners( EventType.LOAD, new SecuredLoadEntityListener() );
Customer customer = entityManager.find( Customer.class, customerId );
public static class SecuredLoadEntityListener implements LoadEventListener {
// this is the single method defined by the LoadEventListener interface
public void onLoad(LoadEvent event, LoadType loadType)
throws HibernateException {
if ( !Principal.isAuthorized( event.getEntityClassName(), event.getEntityId() ) ) {
throw new SecurityException( "Unauthorized access" );
}
}
}
14.3. Mixing Events and Interceptors
When you want to customize the entity state transition behavior, you have two options:
-
you provide a custom
Interceptor
, which is taken into consideration by the default Hibernate event listeners.
For example, theInterceptor#onSave()
method is invoked by HibernateAbstractSaveEventListener
.
Or, theInterceptor#onLoad()
is called by theDefaultPreLoadEventListener
. -
you can replace any given default event listener with your own implementation.
When doing this, you should probably extend the default listeners because otherwise, you’d have to take care of all the low-level entity state transition logic.
For example, if you replace theDefaultPreLoadEventListener
with your own implementation, then, only if you call theInterceptor#onLoad()
method explicitly, you can mix the custom load event listener with a custom Hibernate interceptor.
14.4. Jakarta Persistence Callbacks
Jakarta Persistence also defines a more limited set of callbacks through annotations.
Type | Description |
---|---|
@PrePersist |
Executed before the entity manager persist operation is actually executed or cascaded. This call is synchronous with the persist operation. |
@PreRemove |
Executed before the entity manager remove operation is actually executed or cascaded. This call is synchronous with the remove operation. |
@PostPersist |
Executed after the entity manager persist operation is actually executed or cascaded. This call is invoked after the database INSERT is executed. |
@PostRemove |
Executed after the entity manager remove operation is actually executed or cascaded. This call is synchronous with the remove operation. |
@PreUpdate |
Executed before the database UPDATE operation. |
@PostUpdate |
Executed after the database UPDATE operation. |
@PostLoad |
Executed after an entity has been loaded into the current persistence context or an entity has been refreshed. |
There are two available approaches defined for specifying callback handling:
-
The first approach is to annotate methods on the entity itself to receive notifications of a particular entity lifecycle event(s).
-
The second is to use a separate entity listener class.
An entity listener is a stateless class with a no-arg constructor.
The callback annotations are placed on a method of this class instead of the entity class.
The entity listener class is then associated with the entity using thejakarta.persistence.EntityListeners
annotation
Example 522. Example of specifying Jakarta Persistence callbacks
@Entity(name = "Person")
@EntityListeners( LastUpdateListener.class )
public static class Person {
@Id
private Long id;
private String name;
private Date dateOfBirth;
@Transient
private long age;
private Date lastUpdate;
public void setLastUpdate(Date lastUpdate) {
this.lastUpdate = lastUpdate;
}
/**
* Set the transient property at load time based on a calculation.
* Note that a native Hibernate formula mapping is better for this purpose.
*/
@PostLoad
public void calculateAge() {
age = ChronoUnit.YEARS.between( LocalDateTime.ofInstant(
Instant.ofEpochMilli( dateOfBirth.getTime()), ZoneOffset.UTC),
LocalDateTime.now()
);
}
}
public static class LastUpdateListener {
@PreUpdate
@PrePersist
public void setLastUpdate( Person p ) {
p.setLastUpdate( new Date() );
}
}
These approaches can be mixed, meaning you can use both together.
Regardless of whether the callback method is defined on the entity or on an entity listener, it must have a void-return signature.
The name of the method is irrelevant as it is the placement of the callback annotations that makes the method a callback.
In the case of callback methods defined on the entity class, the method must additionally have a no-argument signature.
For callback methods defined on an entity listener class, the method must have a single argument signature; the type of that argument can be either java.lang.Object
(to facilitate attachment to multiple entities) or the specific entity type.
A callback method can throw a RuntimeException
.
If the callback method does throw a RuntimeException
, then the current transaction, if any, must be rolled back.
A callback method must not invoke EntityManager
or Query
methods!
It is possible that multiple callback methods are defined for a particular lifecycle event.
When that is the case, the defined order of execution is well defined by the Jakarta Persistence spec (specifically section 3.5.4):
-
Any default listeners associated with the entity are invoked first, in the order they were specified in the XML. See the
jakarta.persistence.ExcludeDefaultListeners
annotation. -
Next, entity listener class callbacks associated with the entity hierarchy are invoked, in the order they are defined in the
EntityListeners
.
If multiple classes in the entity hierarchy define entity listeners, the listeners defined for a superclass are invoked before the listeners defined for its subclasses.
See thejakarta.persistence.ExcludeSuperclassListener
‘s annotation. -
Lastly, callback methods defined on the entity hierarchy are invoked.
If a callback type is annotated on both an entity and one or more of its superclasses without method overriding, both would be called, the most general superclass first.
An entity class is also allowed to override a callback method defined in a superclass in which case the super callback would not get invoked; the overriding method would get invoked provided it is annotated.
14.5. Default entity listeners
The Jakarta Persistence specification allows you to define a default entity listener which is going to be applied for every entity in that particular system.
Default entity listeners can only be defined in XML mapping files.
Example 523. Default event listener mapping
public class DefaultEntityListener {
public void onPersist(Object entity) {
if (entity instanceof BaseEntity) {
BaseEntity baseEntity = (BaseEntity) entity;
baseEntity.setCreatedOn(now());
}
}
public void onUpdate(Object entity) {
if (entity instanceof BaseEntity) {
BaseEntity baseEntity = (BaseEntity) entity;
baseEntity.setUpdatedOn(now());
}
}
private Timestamp now() {
return Timestamp.from(
LocalDateTime.now().toInstant(ZoneOffset.UTC)
);
}
}
<entity-mappings xmlns="http://xmlns.jcp.org/xml/ns/persistence/orm"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence/orm
http://xmlns.jcp.org/xml/ns/persistence/orm_2_1.xsd"
version="2.1">
<persistence-unit-metadata>
<persistence-unit-defaults>
<entity-listeners>
<entity-listener
class="org.hibernate.orm.test.events.DefaultEntityListener">
<pre-persist method-name="onPersist"/>
<pre-update method-name="onUpdate"/>
</entity-listener>
</entity-listeners>
</persistence-unit-defaults>
</persistence-unit-metadata>
</entity-mappings>
Considering that all entities extend the BaseEntity
class:
@MappedSuperclass
public abstract class BaseEntity {
private Timestamp createdOn;
private Timestamp updatedOn;
//Getters and setters are omitted for brevity
}
@Entity(name = "Person")
public static class Person extends BaseEntity {
@Id
private Long id;
private String name;
//Getters and setters omitted for brevity
}
@Entity(name = "Book")
public static class Book extends BaseEntity {
@Id
private Long id;
private String title;
@ManyToOne
private Person author;
//Getters and setters omitted for brevity
}
When persisting a Person
or Book
entity, the createdOn
is going to be set by the onPersist
method of the DefaultEntityListener
.
Example 524. Default event listener persist event
Person author = new Person();
author.setId(1L);
author.setName("Vlad Mihalcea");
entityManager.persist(author);
Book book = new Book();
book.setId(1L);
book.setTitle("High-Performance Java Persistence");
book.setAuthor(author);
entityManager.persist(book);
insert
into
Person
(createdOn, updatedOn, name, id)
values
(?, ?, ?, ?)
-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.224]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [4] as [BIGINT] - [1]
insert
into
Book
(createdOn, updatedOn, author_id, title, id)
values
(?, ?, ?, ?, ?)
-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.246]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [BIGINT] - [1]
-- binding parameter [4] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [5] as [BIGINT] - [1]
When updating a Person
or Book
entity, the updatedOn
is going to be set by the onUpdate
method of the DefaultEntityListener
.
Example 525. Default event listener update event
Person author = entityManager.find(Person.class, 1L);
author.setName("Vlad-Alexandru Mihalcea");
Book book = entityManager.find(Book.class, 1L);
book.setTitle("High-Performance Java Persistence 2nd Edition");
update
Person
set
createdOn=?,
updatedOn=?,
name=?
where
id=?
-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.224]
-- binding parameter [2] as [TIMESTAMP] - [2017-06-08 19:23:48.316]
-- binding parameter [3] as [VARCHAR] - [Vlad-Alexandru Mihalcea]
-- binding parameter [4] as [BIGINT] - [1]
update
Book
set
createdOn=?,
updatedOn=?,
author_id=?,
title=?
where
id=?
-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.246]
-- binding parameter [2] as [TIMESTAMP] - [2017-06-08 19:23:48.317]
-- binding parameter [3] as [BIGINT] - [1]
-- binding parameter [4] as [VARCHAR] - [High-Performance Java Persistence 2nd Edition]
-- binding parameter [5] as [BIGINT] - [1]
14.5.1. Exclude default entity listeners
If you already registered a default entity listener, but you don’t want to apply it to a particular entity,
you can use the
@ExcludeDefaultListeners
and
@ExcludeSuperclassListeners
Jakarta Persistence annotations.
@ExcludeDefaultListeners
instructs the current class to ignore the default entity listeners for the current entity
while @ExcludeSuperclassListeners
is used to ignore the default entity listeners propagated to the BaseEntity
super-class.
Example 526. Exclude default event listener mapping
@Entity(name = "Publisher")
@ExcludeDefaultListeners
@ExcludeSuperclassListeners
public static class Publisher extends BaseEntity {
@Id
private Long id;
private String name;
//Getters and setters omitted for brevity
}
When persisting a Publisher
entity,
the createdOn
is not going to be set by the onPersist
method of the DefaultEntityListener
because the Publisher
entity was marked with the @ExcludeDefaultListeners
and @ExcludeSuperclassListeners
annotations.
Example 527. Excluding default event listener events
Publisher publisher = new Publisher();
publisher.setId(1L);
publisher.setName("Amazon");
entityManager.persist(publisher);
insert
into
Publisher
(createdOn, updatedOn, name, id)
values
(?, ?, ?, ?)
-- binding parameter [1] as [TIMESTAMP] - [null]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [VARCHAR] - [Amazon]
-- binding parameter [4] as [BIGINT] - [1]
15. Java API for HQL and JPQL
The Hibernate Query Language (HQL) and the Java Persistence Query Language (JPQL) are object-oriented query languages based on SQL and very similar in flavor to SQL.
When we use the term «HQL» here, we usually mean both modern HQL, along with the standard subset defined by the specification. |
HQL is not the only way to write queries in Hibernate:
-
criteria queries offer a Java-based API with greater compile-time typesafety, and
-
native SQL queries are also possible.
However, HQL is the most convenient option for most people most of the time.
The actual query language itself is discussed the next chapter.
This chapter describes the Java APIs for executing HQL and JPQL queries.
Most of this chapter is dedicated to discussing org.hibernate.query.Query
, jakarta.persistence.Query
and
jakarta.persistence.TypedQuery
. These Query
contracts mix the ability to perform selections as well mutations.
Hibernate additionally offers the more targeted SelectionQuery
and MutationQuery
contracts. See
SelectionQuery and MutationQuery for additional details.
15.1. Example domain model
The code examples featured in this chapter, and the next, make use of the following annotated domain model.
Example 528. Examples domain model
@NamedQuery(
name = "get_person_by_name",
query = "select p from Person p where name = :name"
)
@NamedQuery(
name = "get_read_only_person_by_name",
query = "select p from Person p where name = :name",
hints = {
@QueryHint(
name = "org.hibernate.readOnly",
value = "true"
)
}
)
@NamedQuery(
name = "delete_person",
query = "delete Person"
)
@NamedStoredProcedureQuery(
name = "sp_person_phones",
procedureName = "sp_person_phones",
parameters = {
@StoredProcedureParameter(
name = "personId",
type = Long.class,
mode = ParameterMode.IN
),
@StoredProcedureParameter(
name = "personPhones",
type = Class.class,
mode = ParameterMode.REF_CURSOR
)
}
)
@Entity
public class Person {
@Id
@GeneratedValue
private Long id;
private String name;
private String nickName;
private String address;
private LocalDateTime createdOn;
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
private List<Phone> phones = new ArrayList<>();
@ElementCollection
@MapKeyEnumerated(EnumType.STRING)
private Map<AddressType, String> addresses = new HashMap<>();
@Version
private int version;
//Getters and setters are omitted for brevity
}
public enum AddressType {
HOME,
OFFICE
}
@Entity
public class Partner {
@Id
@GeneratedValue
private Long id;
private String name;
@Version
private int version;
//Getters and setters are omitted for brevity
}
@Entity
public class Phone {
@Id
private Long id;
@ManyToOne(fetch = FetchType.LAZY)
private Person person;
@Column(name = "phone_number")
private String number;
@Enumerated(EnumType.STRING)
@Column(name = "phone_type")
private PhoneType type;
@OneToMany(mappedBy = "phone", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Call> calls = new ArrayList<>( );
@OneToMany(mappedBy = "phone")
@MapKey(name = "timestamp")
private Map<LocalDateTime, Call> callHistory = new HashMap<>();
@ElementCollection
private List<LocalDateTime> repairTimestamps = new ArrayList<>( );
//Getters and setters are omitted for brevity
}
public enum PhoneType {
LAND_LINE,
MOBILE;
}
@Entity
@Table(name = "phone_call")
public class Call {
@Id
@GeneratedValue
private Long id;
@ManyToOne
private Phone phone;
@Column(name = "call_timestamp")
private LocalDateTime timestamp;
private int duration;
@ManyToOne
private Payment payment;
//Getters and setters are omitted for brevity
}
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Payment {
@Id
@GeneratedValue
private Long id;
private BigDecimal amount;
private boolean completed;
@ManyToOne
private Account account;
@ManyToOne
private Person person;
//Getters and setters are omitted for brevity
}
@Entity
public class CreditCardPayment extends Payment {
String cardNumber;
public void setCardNumber(String cardNumber) {
this.cardNumber = cardNumber;
}
public String getCardNumber() {
return cardNumber;
}
}
@Entity
public class WireTransferPayment extends Payment {
}
15.2. Obtaining a Query
object
A query may be provided to Hibernate as either:
-
an inline query: the text of the query is passed as a string to the session at runtime, or
-
a named query: the query is specified in an annotation or XML file, and identified by name at runtime.
A Query
object is obtained from the EntityManager
or Hibernate Session
by calling createQuery()
or createNamedQuery()
.
The API for actually executing the query is the same in both cases, as we’re about to see below.
15.2.1. Declaring named queries
Named queries may be defined using the Jakarta Persistence annotation @NamedQuery
.
Example 529. Declaring a named query with a query hint
@NamedQuery(
name = "get_read_only_person_by_name",
query = "select p from Person p where name = :name",
hints = {
@QueryHint(
name = "org.hibernate.readOnly",
value = "true"
)
}
)
Alternatively, Hibernate offers an extended
@NamedQuery
annotation
which allows the specification of additional properties of the query, including flush mode, cacheability, and timeout interval, in a more typesafe way.
Example 530. Declaring a named query using the typesafe annotation
@NamedQuery(
name = "get_phone_by_number",
query = "select p " +
"from Phone p " +
"where p.number = :number",
timeout = 1,
readOnly = true
)
One big advantage to named queries is that they are parsed by Hibernate at startup time, and so some sorts of errors are reported much earlier. |
15.2.2. Flavors of the Query API
To execute a query, you’ll need an instance of the Jakarta Persistence Query
interface, or, even better, of its subinterface TypedQuery
.
Jakarta Persistence Query
and TypedQuery
The EntityManager
offers various operations that return Query
or TypedQuery<T>
, including:
-
EntityManager#createQuery()
, which accepts a query written in HQL, and -
EntityManager#createNamedQuery()
, which accepts the name of a named query.
It’s better to explicitly pass the query result type as a Java |
Example 531. Obtaining a Jakarta Persistence Query
or TypedQuery
reference
Query query = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name"
);
TypedQuery<Person> typedQuery = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class
);
Example 532. Obtaining a Jakarta Persistence Query
or TypedQuery
reference for a named query
@NamedQuery(
name = "get_person_by_name",
query = "select p from Person p where name = :name"
)
Query query = entityManager.createNamedQuery("get_person_by_name");
TypedQuery<Person> typedQuery = entityManager.createNamedQuery("get_person_by_name", Person.class);
Hibernate Query
Hibernate’s Session
interface refines the return types of the operations of EntityManager
which create query objects.
Session#createQuery()
, Session#createNamedQuery()
, and other similar operations all return an instance of the extension org.hibernate.query.Query
.
Some overloaded forms of these operations return a raw type, but in Hibernate 6 all of these have been deprecated, and the use of the raw type |
Hibernate’s Query
interface offers additional operations not available via TypedQuery
, as we’ll see below.
Example 533. Obtaining a Hibernate Query
org.hibernate.query.Query<Person> query = session.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class);
Example 534. Obtaining a Hibernate Query
for a named query
org.hibernate.query.Query<Person> query = session.createNamedQuery(
"get_person_by_name",
Person.class);
15.3. Executing HQL and JPQL queries
Since org.hibernate.query.Query
inherits TypedQuery
, which in turn inherits Query
, usage of the three interfaces is almost identical.
15.3.1. Binding arguments to query parameters
A query may have named parameters or ordinal parameters:
-
named parameters are specified using the syntax
:name
, and -
ordinal parameters are specified using the syntax
?1
,?2
, etc.
If the query has parameters, arguments must be bound to each parameter before the query is executed.
Example 535. Named parameter binding
Query query = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name")
.setParameter("name", "J%");
Query query = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.createdOn > :timestamp")
.setParameter("timestamp", timestamp);
JPQL-style ordinal parameters are numbered from 1
.
Just like with named parameters, a ordinal parameter may appear multiple times in a query.
Example 536. Ordinal parameter binding
TypedQuery<Person> query = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like ?1",
Person.class)
.setParameter(1, "J%");
It’s not a good idea to mix named and ordinal parameters in a single query. |
15.3.2. Executing the query
The Query
interface is used to control the execution of the query.
-
Query#getResultList()
is useful when the query might return zero, or more than one result. -
Query#getSingleResult()
is only for cases where the query always returns exactly one result.
It throws an exception when zero or many results are returned by the database. -
Query#getResultStream()
allows results to be retrieved incrementally, using a database cursor.
Example 537. Executing a query using getResultList()
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class)
.setParameter("name", "J%")
.getResultList();
Example 538. Executing a query using getSingleResult()
Person person = (Person) entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name")
.setParameter("name", "J%")
.getSingleResult();
Example 539. Executing a query using getResultStream()
try(Stream<Person> personStream = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class)
.setParameter("name", "J%")
.getResultStream()) {
List<Person> persons = personStream
.skip(5)
.limit(5)
.collect(Collectors.toList());
}
The |
The very important methods Query#setMaxResults()
and Query#setFirstResult()
are used to limit the number of results and control pagination.
Example 540. Limits and pagination
Person person = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name = :name",
Person.class)
.setParameter("name", "John Doe")
.setMaxResults(1)
.getSingleResult();
List<Person> people = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class)
.setParameter("name", "J%")
.setFirstResult(page*10)
.setMaxResults(10)
.getResultList();
15.3.4. Using query hints to control query execution
When working with the Jakarta Persistence API, advanced control over query execution is possible via named query hints.
For example, we may want to specify an execution timeout or control caching.
Example 541. Query
execution using a query hint
Person query = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class)
// timeout - in milliseconds
.setHint("jakarta.persistence.query.timeout", 2000)
// flush only at commit time
.setFlushMode(FlushModeType.COMMIT)
.setParameter("name", "J%")
.getSingleResult();
Jakarta Persistence defines some standard hints with the prefix jakarta.persistence
, but most hints are provider specific.
Using provider-specific hints limits your program’s portability to only a small degree.
Hint name | Interpretation | Equivalent Hibernate API |
---|---|---|
|
The query timeout, in milliseconds. |
|
|
An |
See Fetching. |
|
An |
See Fetching. |
|
The |
|
|
|
|
|
For a cacheable query, the name of a cache region to use. |
|
|
A comment to apply to the generated SQL. |
|
|
The JDBC fetch size to use. |
|
|
The Hibernate-specific (Where possible, prefer |
|
|
|
|
For named queries, query hints may be specified using the |
15.3.5. Advanced control over query execution
When working directly with a Hibernate Session
, the interface org.hibernate.Query
is used to control the execution of the query.
Whereas we needed to specify some information using query hints when working with the Jakarta Persistence API, here we have typesafe setters:
|
Sets the JDBC-level query timeout. |
|
Sets the JDBC-level fetch size. |
|
Control query caching. |
|
Overrides the session-level cache mode. |
|
Overrides the session-level flush mode. Flushing is covered in detail in Flushing. |
|
Overrides the session-level flush mode. Locking is covered in detail in Locking. |
|
Overrides the session-level default for read-only state. The concept of read-only state is covered in Persistence Contexts. |
|
Adds a comment to the generated SQL. |
|
Add a hint to the generated SQL. |
On the other hand, |
For complete details, see the Query Javadocs.
Example 542. Advanced query control
org.hibernate.query.Query<Person> query = session.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class)
// timeout - in seconds
.setTimeout(2)
// write to L2 caches, but do not read from them
.setCacheMode(CacheMode.REFRESH)
// assuming query cache was enabled for the SessionFactory
.setCacheable(true)
// add a comment to the generated SQL if enabled via the hibernate.use_sql_comments configuration property
.setComment("+ INDEX(p idx_person_name)");
15.3.6. Query result transformers
A program may hook into the process of building the query results by providing a org.hibernate.transform.ResultListTransformer
or org.hibernate.transform.TupleTransformer
.
Hibernate provides several some built-in implementations of these interfaces, for example:
Example 543. Using a ResultListTransformer
See the Javadocs along with the built-in implementations for additional details.
15.3.7. Querying for read-only entities
As explained in entity immutability, fetching entities in read-only mode is more efficient than fetching entities whose state changes might need to be written to the database.
Fortunately, even mutable entities may be fetched in read-only mode, with the benefit of reduced memory footprint and of a faster flushing process.
Read-only entities are skipped by the dirty checking mechanism as illustrated by the following example:
Example 544. Read-only entities query example
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"join c.phone p " +
"where p.number = :phoneNumber ",
Call.class)
.setParameter("phoneNumber", "123-456-7890")
.setHint("org.hibernate.readOnly", true)
.getResultList();
calls.forEach(c -> c.setDuration(0));
select
c.id,
c.duration,
c.phone_id,
c.call_timestamp
from
phone_call c
join
Phone p
on p.id=c.phone_id
where
p.phone_number='123-456-7890'
In this example, no SQL UPDATE
was executed.
The method Query#setReadOnly()
is an alternative to using a Jakarta Persistence query hint:
Example 545. Read-only entities native query example
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"join c.phone p " +
"where p.number = :phoneNumber ",
Call.class)
.setParameter("phoneNumber", "123-456-7890")
.unwrap( org.hibernate.query.Query.class)
.setReadOnly(true)
.getResultList();
15.4. Scrolling and streaming results
The org.hibernate.Query
interface offers two specialized operations for reading query results incrementally, while maintaining an open JDBC ResultSet
mapped to a server-side cursor.
15.4.1. Scrollable result sets
Query#scroll()
returns a org.hibernate.ScrollableResults
which wraps an underlying JDBC scrollable ResultSet
.
Depending on the specified ScrollMode
, and on the capabilities of the JDBC driver, the ScrollableResults
may allow navigation of the ResultSet
in either direction.
If a ScrollableResults
is left unclosed by the application, Hibernate will automatically close the underlying resources when the transaction ends.
However, it’s much better to close the ResultSet
as soon as possible.
Since this method holds the JDBC |
If you plan to use |
15.4.2. Streamed result sets
Similarly, getResultStream()
is a specialized operation for reading query results incrementally, while maintaining an open JDBC ResultSet
mapped to a server-side cursor.
The |
Example 547. Hibernate getResultStream()
with a projection result type
try (Stream<Object[]> persons = session.createQuery(
"select p.name, p.nickName " +
"from Person p " +
"where p.name like :name",
Object[].class)
.setParameter("name", "J%")
.getResultStream()) {
persons.map(row -> new PersonNames((String) row[0], (String) row[1]))
.forEach(this::process);
}
Example 548. Hibernate getResultStream()
with an entity result type
try(Stream<Person> persons = session.createQuery(
"select p " +
"from Person p " +
"where p.name like :name",
Person.class)
.setParameter("name", "J%")
.getResultStream()) {
Map<Phone, List<Call>> callRegistry = persons
.flatMap(person -> person.getPhones().stream())
.flatMap(phone -> phone.getCalls().stream())
.collect(Collectors.groupingBy(Call::getPhone));
process(callRegistry);
}
Hibernate will automatically close the underlying resources (the JDBC ResultSet
) when the transaction ends.
However, it’s much better to close the ResultSet
as soon as possible.
The program should always close a |
15.5. Entity query plan cache
Any entity query, be it JPQL or Criteria API, has to be parsed into an AST (Abstract Syntax Tree) so that Hibernate can generate the proper SQL statement. The entity query compilation takes time, and for this reason, Hibernate offers a query plan cache.
When executing an entity query, Hibernate first checks the plan cache, and only if there’s no plan available, a new one will be computed right away.
The query plan cache can be configured via the following configuration properties:
hibernate.query.plan_cache_max_size
-
This setting gives the maximum number of entries of the plan cache. The default value is 2048.
hibernate.query.plan_parameter_metadata_max_size
-
The setting gives the maximum number of
ParameterMetadataImpl
instances maintained by the query plan cache. TheParameterMetadataImpl
object encapsulates metadata about parameters encountered within a query. The default value is 128.
Now, if you have many JPQL or Criteria API queries, it’s a good idea to increase the query plan cache size so that the vast majority of executing entity queries can skip the compilation phase, therefore reducing execution time.
To get a better understanding of the query plan cache effectiveness, Hibernate offers several statistics you can use. For more details, check out the Query plan cache statistics section.
15.6. SelectionQuery
Hibernate’s SelectionQuery
contract is similar to Query
but only exposes methods which are relevant to selection queries. For example,
it does not expose a #executeUpdate
method. This allows for earlier validation of the query as a selection.
Example 549. Selection query validation
// can be validated while creating the SelectionQuery
SelectionQuery<?> badQuery = session.createSelectionQuery( "delete Person" );
// cannot be validated until execution
Query query = session.createQuery( "delete Person", Person.class );
query.getResultList();
SelectionQuery
may also be used with named-queries
Example 550. NamedQuery selection validation
// can be validated while creating the SelectionQuery
SelectionQuery<?> badQuery = session.getNamedQuery( "delete_Person" );
// cannot be validated until execution
Query query = session.getNamedQuery( "delete_Person" );
query.getResultList();
15.7. MutationQuery
Along the same lines as SelectionQuery
, MutationQuery
is similar to Query
but only exposes methods which are relevant to mutation queries.
For example, in terms of execution, it only exposes #executeUpdate
method. This allows for earlier validation of the query as a mutation.
Example 551. Mutation query validation
// can be validated while creating the MutationQuery
MutationQuery badQuery = session.createMutationQuery( "select p from Person p" );
// cannot be validated until execution
Query<Person> query = session.createQuery( "select p from Person p", Person.class );
query.executeUpdate();
MutationQuery
may also be used with named-queries
Example 552. NamedQuery mutation validation
// can be validated while creating the MutationQuery
MutationQuery badQuery = session.createNamedMutationQuery( "get_person_by_name" );
// cannot be validated until execution
Query query = session.createNamedQuery( "get_person_by_name", Person.class );
query.getResultList();
16. Hibernate Query Language
This chapter describes Hibernate Query Language (HQL) and Jakarta Persistence Query Language (JPQL).
JPQL was inspired by early versions of HQL, and is a subset of modern HQL. If strict Jakarta Persistence compliance is desired, use the setting |
HQL (and JPQL) are loosely based on SQL and are easy to learn for anyone familiar with SQL.
16.1. Identifiers and case sensitivity
An identifier is a name used to refer to an entity, an attribute of a Java class, an identification variable, or a function.
For example, Person
, name
, p
, and upper
are all identifiers, but they refer to different kinds of things.
In HQL and JPQL, the case sensitivity of an identifier depends on the kind of thing the identifier refers to.
The rules for case sensitivity are:
-
keywords and function names are case-insensitive, but
-
identification variable names, Java class names, and the names of attributes of Java classes, are case-sensitive.
Incidentally, it’s standard practice to use lowercase keywords in HQL and JPQL. The use of uppercase keywords indicates an endearing but unhealthy attachment to the culture of the 1970’s. |
Just to reiterate these rules:
-
select
,SeLeCT
,sELEct
, andSELECT
are all the same, and also -
upper(name)
andUPPER(name)
are the same, but -
from BackPack
andfrom Backpack
are different, referring to different Java classes, and similarly, -
person.nickName
andperson.nickname
are different, since the path expression elementnickName
refers to an attribute of an entity defined in Java, and finally, -
person.nickName
,Person.nickName
, andPERSON.nickName
are also all different, since the first element of a path expression is an identification variable.
The JPQL specification defines identification variables as case-insensitive. And so in strict JPA-compliant mode, Hibernate treats |
A quoted identifier is written in backticks. Quoting lets you use a keyword as an identifier, for example thing.`select`
.
16.2. Statement types
HQL features four different kinds of statement:
-
select
queries, -
update
statements, -
delete
statements, and -
insert … values
andinsert … select
statements.
The effect of an It is the responsibility of the application to maintain synchronization of state held in memory with the database after execution of an |
16.2.1. Select statements
The full BNF for a select
query is quite complicated.
selectStatement
: queryExpression
queryExpression
: withClause? orderedQuery (setOperator orderedQuery)*
orderedQuery
: (query | "(" queryExpression ")") queryOrder?
query
: selectClause fromClause? whereClause? (groupByClause havingClause?)?
| fromClause whereClause? (groupByClause havingClause?)? selectClause?
queryOrder
: orderByClause limitClause? offsetClause? fetchClause?
fromClause
: FROM entityWithJoins ("," entityWithJoins)*
entityWithJoins
: fromRoot (join | crossJoin | jpaCollectionJoin)*
fromRoot
: entityName variable?
| "LATERAL"? "(" subquery ")" variable?
join
: joinType "JOIN" "FETCH"? joinTarget joinRestriction?
joinTarget
: path variable?
| "LATERAL"? "(" subquery ")" variable?
withClause
: "WITH" cte ("," cte)*
;
cte
: identifier AS ("NOT"? "MATERIALIZED")? "(" queryExpression ")" searchClause? cycleClause?
;
cteAttributes
: identifier ("," identifier)*
;
searchClause
: "SEARCH" ("BREADTH"|"DEPTH") "FIRST BY" searchSpecifications "SET" identifier
;
searchSpecifications
: searchSpecification ("," searchSpecification)*
;
searchSpecification
: identifier sortDirection? nullsPrecedence?
;
cycleClause
: "CYCLE" cteAttributes "SET" identifier ("TO" literal "DEFAULT" literal)? ("USING" identifier)?
;
Most of the complexity here arises from the interplay of set operators (union
, intersect
, and except
) with sorting.
We’ll describe the various clauses of a query later in this chapter, but to summarize, a query might have:
-
a
with
clause, specifying named subqueries to be used in the following query, -
a
select
list, specifying a projection (the things to return from the query), -
a
from
clause and joins, specifying the entities involved in the query, and how they’re related to each other, -
a
where
clause, specifying a restriction, -
a
group by
clause, for aggregation, -
a
having
clause, specifying a restriction to apply after aggregation, -
set operators applied to the results of multiple subqueries,
-
an
order by
clause, for sorting the results, and even -
a
limit
/offset
clause, for limiting or paginating the results.
Every one of these clauses is optional!
For example, the simplest query in HQL has no select
clause at all:
List<Person> persons = session.createQuery(
"from Person", Person.class)
.getResultList();
We don’t necessarily recommend leaving off the select
list.
HQL doesn’t require a Naturally, the previous query may be written with a
When there’s no explicit
For complicated queries, it’s probably best to explicitly specify a |
An alternative «simplest» query has only a select
list:
LocalDateTime datetime = session.createQuery(
"select local datetime",
LocalDateTime.class)
.getSingleResult();
This results in a SQL from dual
query (or equivalent).
Looking carefully at the BNF given above, you might notice that the Of course, standard SQL, and JPQL, require that the
This form of the query is more readable, because the alias is declared before it’s used, just as God and nature intended. |
16.2.2. Update statements
The BNF for an update
statement is much easier to understand:
updateStatement
: "UPDATE" "VERSIONED"? targetEntity setClause whereClause?
targetEntity
: entityName variable?
setClause
: "SET" assignment ("," assignment)*
assignment
: simplePath "=" expression
The set
clause has a list of assignments to attributes of the given entity.
For example:
entityManager.createQuery(
"update Person set nickName = 'Nacho' " +
"where name = 'Ignacio'")
.executeUpdate();
An update
statement must be executed using Query#executeUpdate()
.
A single HQL update
statement might result in multiple SQL update statements executed against the database.
int updatedEntities = entityManager.createQuery(
"update Person p " +
"set p.name = :newName " +
"where p.name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
int updatedEntities = session.createMutationQuery(
"update Person " +
"set name = :newName " +
"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
The integer value returned by executeUpdate()
indicates the number of entity instances affected by the operation.
In a |
An update
statement, by default, does not affect the @Version
column of the affected entities.
Adding the keyword versioned
—writing update versioned
—specifies that Hibernate should update the version or update timestamp.
|
int updatedEntities = session.createMutationQuery(
"update versioned Person " +
"set name = :newName " +
"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
Update statements are polymorphic, and affect mapped subclasses of the given entity class.
No |
16.2.3. Delete statements
The BNF for a delete
statement is also quite simple:
deleteStatement
: "DELETE" "FROM"? targetEntity whereClause?
A delete
statement is executed by calling Query#executeUpdate()
.
A single HQL delete
statement might result in multiple SQL delete statements executed against the database.
The integer value returned by executeUpdate()
indicates the number of entity instances affected by the operation.
Delete statements are polymorphic, and affect mapped subclasses of the given entity class.
16.2.4. Insert statements
There are two kinds of insert
statement:
-
insert … values
, where the attribute values to insert are given directly as tuples, and -
insert … select
, where the inserted attribute values are sourced from a subquery.
The first form inserts a single row in the database, or multiple rows if you provide multiple tuples in the values
clause.
The second form may insert many new rows, or none at all.
The first sort of On the other hand, you might consider using it to set up test data. |
The BNF for an insert
statement is:
insertStatement
: "INSERT" "INTO"? targetEntity targetFields (queryExpression | valuesList)
targetEntity
: entityName variable?
targetFields
: "(" simplePath ("," simplePath)* ")"
valuesList
: "VALUES" values ("," values)*
values
: "(" expression ("," expression)* ")"
For example:
entityManager.createQuery(
"insert Person (id, name) " +
"values (100L, 'Jane Doe')")
.executeUpdate();
entityManager.createQuery(
"insert Person (id, name) " +
"values (101L, 'J A Doe III'), " +
"(102L, 'J X Doe'), " +
"(103L, 'John Doe, Jr')")
.executeUpdate();
int insertedEntities = session.createMutationQuery(
"insert into Partner (id, name) " +
"select p.id, p.name " +
"from Person p ")
.executeUpdate();
An insert
statement must be executed by calling Query#executeUpdate()
.
An |
The queryExpression
may be any valid select
query, with the caveat that the types of the values in the select
list must match the types of the target fields.
This is checked during query compilation rather than allowing the type check to delegate to the database. |
There are two ways to assign a value to the @Id
attribute:
-
explicitly specify the id attribute in the list of target fields, and its value in the values assigned to the target fields, or
-
omit it, in which case a generated value is used.
Of course, the second option is only available for entities with database-level id generation (sequences or identity/autoincrement columns).
It’s not available for entities whose id generator is implemented in Java, nor for entities whose id is assigned by the application.
The same two options are available for a @Version
attribute.
When no version is explicitly specified, the version for a new entity instance is used.
|
16.3. Literals
We now switch gears, and begin describing the language from the bottom up.
The very bottom of a programming language is its syntax for literal values.
The most important literal value in this language is null
. It’s assignable to any other type.
16.3.1. Boolean literals
The boolean literal values are the (case-insensitive) keywords true
and false
.
16.3.2. String literals
String literals are enclosed in single quotes.
To escape a single quote within a string literal, use a doubled single quote: ''
.
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like 'Joe'",
Person.class)
.getResultList();
// Escaping quotes
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like 'Joe''s'",
Person.class)
.getResultList();
16.3.3. Numeric literals
Numeric literals come in several different forms.
// simple integer literal
Person person = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.id = 1",
Person.class)
.getSingleResult();
// simple integer literal, typed as a long
Person person = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.id = 1L",
Person.class)
.getSingleResult();
// decimal notation
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where c.duration > 100.5",
Call.class)
.getResultList();
// decimal notation, typed as a float
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where c.duration > 100.5F",
Call.class)
.getResultList();
// scientific notation
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where c.duration > 1e+2",
Call.class)
.getResultList();
// scientific notation, typed as a float
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where c.duration > 1e+2F",
Call.class)
.getResultList();
The type of a numeric literal may be specified using a Java-style postfix:
Postfix | Type | Java type |
---|---|---|
|
long integer |
|
|
double precision |
|
|
single precision |
|
|
large integer |
|
|
exact decimal |
|
It’s not usually necessary to specify the precision explicitly.
In a literal with an exponent, the |
Hexadecimal literals may be written using the same syntax as Java: 0X1A2B
or 0x1a2b
.
16.3.4. Date and time literals
According to the JPQL specification, date and time literals may be specified using the JDBC escape syntax.
Since this syntax is rather unpleasant to look at, HQL provides not one, but two alternatives.
Date/time type | Recommended Java type | JDBC escape syntax | Braced literal syntax | Explicitly typed literal syntax |
---|---|---|---|---|
Date |
|
|
|
|
Time |
|
|
|
|
Time with seconds |
|
|
|
|
Datetime |
|
|
|
|
Datetime with milliseconds |
|
|
|
|
Datetime with an offset |
|
|
|
|
Datetime with a time zone |
|
|
|
|
Literals referring to the current date and time are also provided.
Again there is some flexibility.
Date/time type | Java type | Underscore syntax | Spaced syntax |
---|---|---|---|
Date |
|
|
|
Time |
|
|
|
Datetime |
|
|
|
Offset datetime |
|
|
|
Instant |
|
|
|
Date |
|
|
|
Time |
|
|
|
Datetime |
|
|
|
Of these, only local date
, local time
, local datetime
, current_date
, current_time
, and current_timestamp
are defined by the JPQL specification.
The use of date and time types from the |
16.3.5. Duration literals
There are two sorts of duration in HQL:
-
year/quarter/month/week/day durations, and
-
week/day/hour/minute/second/nanosecond durations.
Literal duration expressions are of form n unit
, for example 1 day
or 10 year
or 100 nanosecond
.
The unit may be: day
, month
, quarter
, year
, second
, minute
, hour
, or nanosecond
.
A HQL duration is considered to map to a Java |
16.3.6. Binary string literals
HQL also provides a choice of formats for binary strings:
-
the braced syntax
{0xDE, 0xAD, 0xBE, 0xEF}
, a list of Java-style hexadecimal byte literals, or -
the quoted syntax
X’DEADBEEF'
orx’deadbeef'
, similar to SQL.
16.3.7. Enum literals
Literal values of a Java enumerated type may be written without needing to specify the enum class name:
// select clause date/time arithmetic operations
List<Phone> phones1 = entityManager.createQuery(
"from Phone ph " +
"where ph.type = LAND_LINE",
Phone.class)
.getResultList();
Here, the enum class is inferred from the type of the expression on the left of the relational operator.
16.3.8. Java constants
HQL allows any Java static
constant to be used in HQL, but it must be referenced by its fully-qualified name:
// select clause date/time arithmetic operations
Double pi = entityManager.createQuery(
"select java.lang.Math.PI",
Double.class)
.getSingleResult();
16.3.9. Literal entity names
Entity names may also occur as a literal value. They do not need to be qualified. See Types and typecasts.
16.4. Expressions
Essentially, expressions are references that resolve to basic or tuple values.
16.4.1. String concatenation
HQL defines two ways to concatenate strings:
-
the SQL-style concatenation operator,
||
, and -
the JPQL-standard
concat()
function.
See below for details of the concat()
function.
String name = entityManager.createQuery(
"select 'Customer ' || p.name " +
"from Person p " +
"where p.id = 1",
String.class)
.getSingleResult();
Many more operations on strings are defined below, in Functions.
16.4.2. Numeric arithmetic
The basic SQL arithmetic operators, +
,-
,*
, and /
are joined by the remainder operator %
.
// select clause date/time arithmetic operations
Long duration = entityManager.createQuery(
"select sum(ch.duration) * :multiplier " +
"from Person pr " +
"join pr.phones ph " +
"join ph.callHistory ch " +
"where ph.id = 1L ",
Long.class)
.setParameter("multiplier", 1000L)
.getSingleResult();
// select clause date/time arithmetic operations
Integer years = entityManager.createQuery(
"select year(local date) - year(p.createdOn) " +
"from Person p " +
"where p.id = 1L",
Integer.class)
.getSingleResult();
// where clause arithmetic operations
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where year(local date) - year(p.createdOn) > 1",
Person.class)
.getResultList();
The following rules apply to the result of arithmetic operations:
-
If either of the operands is
Double
/double
, the result is aDouble
-
else, if either of the operands is
Float
/float
, the result is aFloat
-
else, if either operand is
BigDecimal
, the result isBigDecimal
-
else, if either operand is
BigInteger
, the result isBigInteger
(except for division, in which case the result type is not further defined) -
else, if either operand is
Long
/long
, the result isLong
(except for division, in which case the result type is not further defined) -
else, (the assumption being that both operands are of integral type) the result is
Integer
(except for division, in which case the result type is not further defined)
Many more numeric operations are defined below, in Functions.
16.4.3. Datetime arithmetic
Arithmetic involving dates, datetimes, and durations is quite subtle.
Here we list the basic operations.
Operator | Expression type | Example | Resulting type |
---|---|---|---|
|
Difference between two dates |
|
year/quarter/month/week/day duration |
|
Difference between two datetimes |
|
week/day/hour/minute/second/nanosecond duration |
|
Sum of a date and a year/quarter/month/week/day duration |
|
date |
|
Sum of a datetime and a week/day/hour/minute/second/nanosecond duration |
|
datetime |
|
Product of an integer and a duration |
|
duration |
|
Convert a duration to an integer |
|
integer |
The by unit
operator converts a duration to an integer, for example: (local date - your.birthday) by day
evaluates to the number of days you still have to wait.
The function extract(unit from …)
extracts a field from a date, time, or datetime type, for example, extract(year from your.birthday)
produces the year in which you were born, and throws away important information about your birthday.
Please carefully note the difference between these two operations: |
Additional datetime operations, including the useful format()
function, are defined below, in Functions.
16.4.4. Identification variables and path expressions
Identification variables, and path expressions beginning with an identification variable are legal expression in almost every context.
16.4.5. Case expressions
Just like in standard SQL, there are two forms of case expression:
-
the simple case expression, and
-
the so-called searched case expression.
Case expressions are verbose. |
Simple case expressions
The syntax of the simple form is defined by:
"CASE" expression ("WHEN" expression "THEN" expression)+ ("ELSE" expression)? END
For example:
List<String> nickNames = entityManager.createQuery(
"select " +
" case p.nickName " +
" when 'NA' " +
" then '<no nick name>' " +
" else p.nickName " +
" end " +
"from Person p",
String.class)
.getResultList();
Searched case expressions
The searched form has the following syntax:
"CASE" ("WHEN" predicate "THEN" expression)+ ("ELSE" expression)? "END"
For example:
List<String> nickNames = entityManager.createQuery(
"select " +
" case " +
" when p.nickName is null " +
" then " +
" case " +
" when p.name is null " +
" then '<no nick name>' " +
" else p.name " +
" end" +
" else p.nickName " +
" end " +
"from Person p",
String.class)
.getResultList();
A case
expression may contain complex expression, including operator expressions:
List<Long> values = entityManager.createQuery(
"select " +
" case when p.nickName is null " +
" then p.id * 1000 " +
" else p.id " +
" end " +
"from Person p " +
"order by p.id",
Long.class)
.getResultList();
assertEquals(3, values.size());
assertEquals(1L, (long) values.get(0));
assertEquals(2000, (long) values.get(1));
assertEquals(3000, (long) values.get(2));
16.5. Functions
Both HQL and JPQL define some standard functions and make them portable between databases.
A program that wishes to remain portable between Jakarta Persistence providers should in principle limit itself to the use of these functions. On the other hand, this is an extremely short list. Any nontrivial program will probably need to look beyond it. |
In some cases, the syntax of these functions looks a bit funny at first, for example, cast(number as String)
, or extract(year from date)
, or even trim(leading '.' from string)
.
This syntax is inspired by standard ANSI SQL, and we promise you’ll get used to it.
HQL abstracts away from the actual database-native SQL functions, letting you write queries which are portable between databases. For some functions, and always depending on the database, a HQL function invocation translates to a quite complicated SQL expression! |
In addition, there are several ways to use a database function that’s not known to Hibernate.
16.5.1. Types and typecasts
The following special functions make it possible to discover or narrow expression types:
Special function | Purpose | Signature | JPA standard |
---|---|---|---|
|
The (concrete) entity name |
|
✓ |
|
Narrow an entity type |
|
✓ |
|
Narrow a basic type |
|
✗ |
|
Cast to a string |
|
✗ |
Let’s see what these functions do.
type()
The function type()
, applied to an identification variable, evaluates to the entity name of the referenced entity.
This is mainly useful when dealing with entity inheritance hierarchies.
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p " +
"where type(p) = CreditCardPayment",
Payment.class)
.getResultList();
// using a parameter instead of a literal entity type
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p " +
"where type(p) = :type",
Payment.class)
.setParameter("type", WireTransferPayment.class)
.getResultList();
treat()
The function treat()
may be used to narrow the type of an identification variable.
This is useful when dealing with entity inheritance hierarchies.
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p " +
"where length(treat(p as CreditCardPayment).cardNumber) between 16 and 20",
Payment.class)
.getResultList();
The type of the expression treat(p as CreditCardPayment)
is the narrowed type, CreditCardPayment
, instead of the declared type Payment
of p
.
This allows the attribute cardNumber
declared by the subtype CreditCardPayment
to be referenced.
The treat()
function may even occur in a join.
cast()
The function cast()
has a similar syntax, but is used to narrow basic types.
Its first argument is usually an attribute of an entity, or a more complex expression involving entity attributes.
The target type is an unqualified Java class name:
String
, Long
, Integer
, Double
, Float
, Character
, Byte
, BigInteger
, BigDecimal
, LocalDate
, LocalTime
, LocalDateTime
, etc.
List<String> durations = entityManager.createQuery(
"select cast(c.duration as String) " +
"from Call c ",
String.class)
.getResultList();
str()
The function str(x)
is a synonym for cast(x as String)
.
List<String> timestamps = entityManager.createQuery(
"select str(c.timestamp) " +
"from Call c ",
String.class)
.getResultList();
// Special SQL Server function "str" that converts floats
List<String> timestamps = entityManager.createQuery(
"select str(cast(duration as float) / 60, 4, 2) " +
"from Call c ",
String.class)
.getResultList();
16.5.2. Functions for working with null values
The following functions make it easy to deal with null values:
Function | Purpose | Signature | JPA standard |
---|---|---|---|
|
First non-null argument |
|
✓ |
|
Second argument if first is null |
|
✗ |
|
|
|
✓ |
coalesce()
An abbreviated case
expression that returns the first non-null operand.
List<String> nickNames = entityManager.createQuery(
"select coalesce(p.nickName, '<no nick name>') " +
"from Person p",
String.class)
.getResultList();
List<String> nickNames = entityManager.createQuery(
"select coalesce(p.nickName, p.name, '<no nick name>') " +
"from Person p",
String.class)
.getResultList();
ifnull()
HQL allows ifnull()
as a synonym for coalesce()
in the case of exactly two arguments.
nullif()
Evaluates to null if its operands are equal, or to its first argument otherwise.
List<String> nickNames = entityManager.createQuery(
"select nullif(p.nickName, p.name) " +
"from Person p",
String.class)
.getResultList();
// equivalent CASE expression
List<String> nickNames = entityManager.createQuery(
"select " +
" case" +
" when p.nickName = p.name" +
" then null" +
" else p.nickName" +
" end " +
"from Person p",
String.class)
.getResultList();
16.5.3. Functions for working with dates and times
There are some very important functions for working with dates and times.
Special function | Purpose | Signature | JPA standard |
---|---|---|---|
|
Extract a datetime field |
|
✓ |
|
Format a datetime as a string |
|
✗ |
|
Datetime truncation |
|
✗ |
The special function extract()
obtains a single field of a date, time, or datetime.
Field types include: day
, month
, year
, second
, minute
, hour
, day of week
, day of month
, week of year
, date
, time
, epoch
and more.
For a full list of field types, see the Javadoc for TemporalUnit
.
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where extract(date from c.timestamp) = local date",
Call.class)
.getResultList();
List<Integer> years = entityManager.createQuery(
"select extract(year from c.timestamp) " +
"from Call c ",
Integer.class)
.getResultList();
The following functions are abbreviations for extract()
:
Function | Long form using extract() |
JPA standard |
---|---|---|
|
|
✗ |
|
|
✗ |
|
|
✗ |
|
|
✗ |
|
|
✗ |
|
|
✗ |
These abbreviations aren’t part of the JPQL standard, but on the other hand they’re a lot less verbose. |
List<Integer> years = entityManager.createQuery(
"select year(c.timestamp) " +
"from Call c ",
Integer.class)
.getResultList();
format()
This function formats a date, time, or datetime according to a pattern.
The syntax is format(datetime as pattern)
, and the pattern must be written in a subset of the pattern language defined by Java’s java.time.format.DateTimeFormatter
.
trunc()
or truncate()
This function truncates a date, time, or datetime to the temporal unit specified by field.
The syntax is truncate(datetime, field)
. Supported temporal units are: year
, month
, day
, hour
, minute
or second
.
Truncating a date, time or datetime value translates to obtaining a value of the same type in which all temporal units smaller than field
have been pruned.
For hours, minutes and second this means setting them to 00
. For months and days, this means setting them to 01
.
16.5.4. Functions for working with strings
Naturally, there are a good number of functions for working with strings.
Function | Purpose | Syntax | JPA standard / ANSI SQL Standard |
---|---|---|---|
|
The string, with lowercase characters converted to uppercase |
|
✓ / ✓ |
|
The string, with uppercase characters converted to lowercase |
|
✓ / ✓ |
|
The length of the string |
|
✓ / ✗ |
|
Concatenate strings |
|
✓ / ✗ |
|
Location of string within a string |
|
✓ / ✗ |
|
Similar to |
|
✗ / ✓ |
|
Substring of a string (JPQL-style) |
|
✓ / ✗ |
|
Substring of a string (ANSI SQL-style) |
|
✗ / ✓ |
|
Trim characters from string |
See below |
✓ / ✓ |
|
For replacing a substring |
|
✗ / ✓ |
|
Pads a string with whitespace, or with a specified character |
|
✗ / ✗ |
|
The leftmost characters of a string |
|
✗ / ✗ |
|
The rightmost characters of a string |
|
✗ / ✗ |
|
Replace every occurrence of a pattern in a string |
|
✗ / ✗ |
|
Concatenate a string with itself multiple times |
|
✗ / ✗ |
|
Select a collation |
|
✗ / ✗ |
Let’s take a closer look at just some of these.
Contrary to Java, positions of characters within strings are indexed from 1 instead of 0! |
concat()
Accepts a variable number of arguments, and produces a string by concatenating them.
List<String> callHistory = entityManager.createQuery(
"select concat(p.number, ' : ' , cast(c.duration as string)) " +
"from Call c " +
"join c.phone p",
String.class)
.getResultList();
locate()
The JPQL function locate()
determines the position of a substring within another string.
-
The optional third argument is used to specify a position at which to start the search.
List<Integer> sizes = entityManager.createQuery(
"select locate('John', p.name) " +
"from Person p ",
Integer.class)
.getResultList();
position()
The position()
function has a similar purpose, but follows the ANSI SQL syntax.
List<Integer> sizes = entityManager.createQuery(
"select position('John' in p.name) " +
"from Person p ",
Integer.class)
.getResultList();
substring()
Returns a substring of the given string.
-
The second argument specifies the position of the first character of the substring.
-
The optional third argument specifies the maximum length of the substring.
// JPQL-style
List<String> prefixes = entityManager.createQuery(
"select substring(p.number, 1, 2) " +
"from Call c " +
"join c.phone p",
String.class)
.getResultList();
// ANSI SQL-style
List<String> prefixes2 = entityManager.createQuery(
"select substring(p.number from 1 for 2) " +
"from Call c " +
"join c.phone p",
String.class)
.getResultList();
trim()
The trim()
function follows the syntax and semantics of ANSI SQL.
It may be used to trim leading
characters, trailing
characters, or both.
// trim whitespace from both ends
List<String> names1 = entityManager.createQuery(
"select trim(p.name) " +
"from Person p ",
String.class)
.getResultList();
// trim leading spaces
List<String> names2 = entityManager.createQuery(
"select trim(leading ' ' from p.name) " +
"from Person p ",
String.class)
.getResultList();
Its BNF is funky:
trimFunction
: "TRIM" "(" trimSpecification? trimCharacter? "FROM"? expression ")" ;
trimSpecification
: "LEADING" | "TRAILING" | "BOTH" ;
collate()
Selects a collation to be used for its string-valued argument.
Collations are useful for binary comparisons with <
or >
, and in the order by clause.
For example, collate(p.name as ucs_basic)
specifies the SQL standard collation ucs_basic
.
Collations aren’t very portable between databases. |
16.5.5. Numeric functions
Of course, we also have a number of functions for working with numeric values.
Function | Purpose | Signature | JPA standard |
---|---|---|---|
|
The magnitude of a number |
|
✓ |
|
The sign of a number |
|
✓ |
|
Remainder of integer division |
|
✓ |
|
Square root of a number |
|
✓ |
|
Exponential function |
|
✓ |
|
Exponentiation |
|
✓ |
|
Natural logarithm |
|
✓ |
|
Numeric rounding |
|
✓ |
|
Numeric truncation |
|
✗ |
|
Floor function |
|
✓ |
|
Ceiling function |
|
✓ |
|
Base-10 logarithm |
|
✗ |
|
Arbitrary-base logarithm |
|
✗ |
|
π |
|
✗ |
|
Basic trigonometric functions |
|
✗ |
|
Two-argument arctangent (range |
|
✗ |
|
Hyperbolic functions |
|
✗ |
|
Convert radians to degrees |
|
✗ |
|
Convert degrees to radians |
|
✗ |
|
Return the smallest of the given arguments |
|
✗ |
|
Return the largest of the given arguments |
|
✗ |
List<Integer> abs = entityManager.createQuery(
"select abs(c.duration) " +
"from Call c ",
Integer.class)
.getResultList();
List<Integer> mods = entityManager.createQuery(
"select mod(c.duration, 10) " +
"from Call c ",
Integer.class)
.getResultList();
List<Double> sqrts = entityManager.createQuery(
"select sqrt(c.duration) " +
"from Call c ",
Double.class)
.getResultList();
We haven’t included aggregate functions, ordered set aggregate functions, or Window functions: over
in this list, because their purpose is more specialized, and because they come with extra special syntax.
16.5.6. Functions for dealing with collections
The following functions apply to any identification variable that refers to a joined collection.
Function | Purpose | JPA standard |
---|---|---|
|
The size of a collection |
✗ |
|
The element of a list |
✗ |
|
The index of a list element |
✗ |
|
The key of a map entry |
✗ |
|
The value of a map entry |
✗ |
|
The whole entry in a map |
✗ |
|
See below |
✗ |
|
See below |
✗ |
size()
The number of elements of a collection or to-many association.
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where size(p.phones) >= 2",
Person.class)
.getResultList();
element()
and index()
A reference to an element or index of joined list.
key()
, value()
, and entry()
A reference to a key, value, or entry of a joined map.
elements()
, and indices()
Later, in Elements and indices, and in Aggregate functions and collections, we will learn about these special functions for quantifying over the elements or indices of a particular collection.
16.5.7. Functions for working with ids and versions
Finally, the following functions evaluate the id, version, or natural id of an entity, or the foreign key of a to-one association:
Function | Purpose | JPA standard |
---|---|---|
|
The value of the entity |
✗ |
|
The value of the entity |
✗ |
|
The value of the entity |
✗ |
|
The value of the foreign key column mapped by a |
✗ |
16.5.8. Native and user-defined functions
The functions we’ve described above are the functions abstracted by HQL and made portable across databases.
But, of course, HQL can’t abstract every function in your database.
There are several ways to call native or user-defined SQL functions.
-
A native or user-defined function may be called using JPQL’s
function
syntax, for example,function('sinh', phi)
.
(This is the easiest way, but not the best way.) -
A user-written
FunctionContributor
may register user-defined functions. -
A custom
Dialect
may register additional native functions by overridinginitializeFunctionRegistry()
.
Registering a function isn’t hard, but is beyond the scope of this chapter. (It’s even possible to use the APIs Hibernate provides to make your own portable functions!) |
Fortunately, every built-in Dialect
already registers many native functions for the database it supports.
Try setting the log category |
// careful: these functions are not supported on all databases!
List<Tuple> variances = entityManager.createQuery(
"select var_samp(c.duration) as sampvar, var_pop(c.duration) as popvar " +
"from Call c ",
Tuple.class)
.getResultList();
List<Number> bits = entityManager.createQuery(
"select bit_length(c.phone.number) " +
"from Call c ",
Number.class)
.getResultList();
16.5.9. Embedding native SQL in HQL
The special function sql()
allows the use of native SQL fragments inside an HQL query.
The signature of this function is sql(pattern[, argN]*)
, where pattern
must be a string literal but the remaining arguments may be of any type.
The pattern literal is unquoted and embedded in the generated SQL.
Occurrences of ?
in the pattern are replaced with the remaining arguments of the function.
-- Cast to some native type
select c from Computer c where c.ipAddress = sql('?::inet', '127.0.0.1')
-- Use some native operator
select h from Human h order by sql('(? <-> ?)', h.workLocation, h.homeLocation)
16.6. Predicates
A predicate is an operator which, when applied to some argument, evaluates to true
or false
.
In the world of SQL-style ternary logic, we must expand this definition to encompass the possibility that the predicate evaluates to null
.
Typically, a predicate evaluates to null
when one of its arguments is null
.
Predicates occur in the where
clause, the having
clause and in searched case expressions.
16.6.1. Relational operators
The binary comparison operators are borrowed from SQL: =
, >
, >=
, <
, <=
, <>
.
If you prefer, HQL treats != as a synonym for <> .
|
The operands should be of the same type.
// numeric comparison
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where c.duration < 30 ",
Call.class)
.getResultList();
// string comparison
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like 'John%' ",
Person.class)
.getResultList();
// datetime comparison
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.createdOn > date 1950-01-01 ",
Person.class)
.getResultList();
// enum comparison
List<Phone> phones = entityManager.createQuery(
"select p " +
"from Phone p " +
"where p.type = 'MOBILE' ",
Phone.class)
.getResultList();
// boolean comparison
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p " +
"where p.completed = true ",
Payment.class)
.getResultList();
// boolean comparison
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p " +
"where type(p) = WireTransferPayment ",
Payment.class)
.getResultList();
// entity value comparison
List<Object[]> phonePayments = entityManager.createQuery(
"select p " +
"from Payment p, Phone ph " +
"where p.person = ph.person ",
Object[].class)
.getResultList();
16.6.2. between
The ternary between
operator, and its negation, not between
, determine if a value falls within a range.
Of course, all three operands must be of compatible type.
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"join p.phones ph " +
"where p.id = 1L and index(ph) between 0 and 3",
Person.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.createdOn between date 1999-01-01 and date 2001-01-02",
Person.class)
.getResultList();
List<Call> calls = entityManager.createQuery(
"select c " +
"from Call c " +
"where c.duration between 5 and 20",
Call.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name between 'H' and 'M'",
Person.class)
.getResultList();
16.6.3. Operators for dealing with null
The following operators make it easier to deal with null values.
Operator | Negation | Type | Semantics |
---|---|---|---|
|
|
Unary postfix |
|
|
|
Binary |
|
// select all persons with a nickname
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.nickName is not null",
Person.class)
.getResultList();
// select all persons without a nickname
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.nickName is null",
Person.class)
.getResultList();
16.6.4. Operators for dealing with boolean values
These operators perform comparisons on values of type boolean
.
These predicates never evaluate to null
.
The values |
For logical operations on predicates, see [logical-operators] below.
Operator | Negation | Type | Semantics |
---|---|---|---|
|
|
Unary postfix |
|
|
|
Binary |
|
16.6.5. String pattern matching
The like
operator performs pattern matching on strings.
Its friend ilike
performs case-insensitive matching.
Their syntax is defined by:
expression "NOT"? ("LIKE" | "ILIKE") expression ("ESCAPE" character)?
The expression on the right is a pattern, where:
-
_
matches any single character, -
%
matches any number of characters, and -
if an escape character is specified, it may be used to escape either of these wildcards.
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like 'Jo%'",
Person.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name not like 'Jo%'",
Person.class)
.getResultList();
The optional escape
character allows a pattern to include a literal _
or %
character.
For example, to match all stored procedures prefixed with Dr_
, the like criteria could be 'Dr|_%' escape '|'
:
// find any person with a name starting with "Dr_"
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.name like 'Dr|_%' escape '|'",
Person.class)
.getResultList();
As you can guess, not like
and not ilike
are the enemies of like
and ilike
, and evaluate to the exact opposite boolean values.
16.6.6. Elements and indices
There’s two special HQL functions that we mentioned earlier, without giving much of an explanation, since they’re only useful in conjunction with the predicate operators we’re about to meet.
These functions are only allowed in the where
clause, and result in a subquery in the generated SQL.
Indeed, you can think of them as just a shortcut way to write a subquery.
HQL Function | Applies to | Purpose |
---|---|---|
|
Any collection |
Refers to the elements of a collection as a whole. |
|
Indexed collections (lists and maps) |
Similar to |
In the next three sections, we’ll see how these two functions are useful.
16.6.7. in
The in
predicates evaluates to true if the value to its left is in … well, whatever it finds to its right.
Its syntax is unexpectedly complicated:
expression "NOT"? "IN" inList
inList
: ("ELEMENTS"|"INDICES") "(" simplePath ")"
| "(" (expression ("," expression)*)? ")"
| "(" subquery ")"
| parameter
This less-than-lovely fragment of the HQL ANTLR grammar tells is that the thing to the right might be:
-
a list of values enclosed in parentheses,
-
a query parameter,
-
a subquery, or
-
one of the functions
elements()
orindices()
defined above.
The type of the expression on the left, and the types of all the values on the right must be compatible.
JPQL limits the legal types to string, numeric, date/time, and enum types, and in JPQL the left expression must be either:
HQL is far more permissive. HQL itself does not restrict the type any way, though the database itself might. |
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p " +
"where type(p) in (CreditCardPayment, WireTransferPayment)",
Payment.class)
.getResultList();
List<Phone> phones = entityManager.createQuery(
"select p " +
"from Phone p " +
"where type in ('MOBILE', 'LAND_LINE')",
Phone.class)
.getResultList();
List<Phone> phones = entityManager.createQuery(
"select p " +
"from Phone p " +
"where type in :types",
Phone.class)
.setParameter("types", Arrays.asList(PhoneType.MOBILE, PhoneType.LAND_LINE))
.getResultList();
List<Phone> phones = entityManager.createQuery(
"select distinct p " +
"from Phone p " +
"where p.person.id in (" +
" select py.person.id " +
" from Payment py" +
" where py.completed = true and py.amount > 50 " +
")",
Phone.class)
.getResultList();
// Not JPQL compliant!
List<Phone> phones = entityManager.createQuery(
"select distinct p " +
"from Phone p " +
"where p.person in (" +
" select py.person " +
" from Payment py" +
" where py.completed = true and py.amount > 50 " +
")",
Phone.class)
.getResultList();
// Not JPQL compliant!
List<Payment> payments = entityManager.createQuery(
"select distinct p " +
"from Payment p " +
"where (p.amount, p.completed) in (" +
" (50, true)," +
" (100, true)," +
" (5, false)" +
")", Payment.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where 1 in indices(p.phones)",
Person.class)
.getResultList();
16.6.8. Relational operators and subqueries
The binary comparisons we met above in Relational operators may involve a qualifier:
-
a qualified subquery, or
-
a qualifier applied to one of the functions
elements()
orindices()
defined above.
The qualifiers are unary prefix operators: all
, every
, any
, and some
.
Subquery operator | Synonym | Semantics |
---|---|---|
|
|
Evaluates to true of the comparison is true for every value in the result set of the subquery. |
|
|
Evaluates to true of the comparison is true for at least one value in the result set of the subquery. |
// select all persons with all calls shorter than 50 seconds
List<Person> persons = entityManager.createQuery(
"select distinct p.person " +
"from Phone p " +
"join p.calls c " +
"where 50 > all (" +
" select duration" +
" from Call" +
" where phone = p " +
") ", Person.class)
.getResultList();
List<Phone> phones = entityManager.createQuery(
"select p " +
"from Phone p " +
"where local date > all elements(p.repairTimestamps)",
Phone.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where :phone = some elements(p.phones)",
Person.class)
.setParameter("phone", phone)
.getResultList();
// the above query can be re-written with member of
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where :phone member of p.phones",
Person.class)
.setParameter("phone", phone)
.getResultList();
16.6.9. Exists operator
The unary prefix exists
operator evaluates to true if the thing to its right is nonempty.
The thing to its right might be:
-
a subquery, or
-
one of the functions
elements()
orindices()
defined above.
As you can surely guess, not exists
evaluates to true if the thing to the right is empty.
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where exists elements(p.phones)",
Person.class)
.getResultList();
16.6.10. Collection operators
The following operators apply to collection-valued attributes and to-many associations.
Operator | Negation | Type | Semantics |
---|---|---|---|
|
|
Unary postfix |
|
|
|
Binary |
|
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.phones is empty",
Person.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.phones is not empty",
Person.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where 'Home address' member of p.addresses",
Person.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where 'Home address' not member of p.addresses",
Person.class)
.getResultList();
16.6.11. Logical operators
The logical operators are binary infix and
and or
, and unary prefix not
.
Just like SQL, logical expressions are based on ternary logic.
A logical operator evaluates to null if it has a null operand.
16.7. Declaring root entities: from
and cross join
The from
clause is responsible for declaring the entities available in the rest of the query, and assigning them aliases, or, in the language of the JPQL specification, identification variables.
16.7.1. Identification variables
An identification variable is just a name we can use to refer to an entity and its attributes from expressions in the query.
It may be any legal Java identifier.
According to the JPQL specification, identification variables must be treated as case-insensitive language elements.
The identification variable is actually optional, but for queries involving more than one entity it’s almost always a good idea to declare one. |
Identification variables may be declared with the as
keyword, but this is optional.
16.7.2. Root entity references
A root entity reference, or what the JPQL specification calls a range variable declaration, is a direct reference to a mapped @Entity
type by its entity name.
Remember, the entity name is the value of the |
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p",
Person.class)
.getResultList();
In this example, Person
is the entity name, and p
is the identification variable.
Alternatively, a fully-qualified Java class name may be specified.
Then Hibernate will query every entity which inherits the named type.
List<Person> persons = entityManager.createQuery(
"select p " +
"from org.hibernate.testing.orm.domain.userguide.Person p",
Person.class)
.getResultList();
Of course, there may be multiple root entities.
List<Object[]> persons = entityManager.createQuery(
"select distinct pr, ph " +
"from Person pr, Phone ph " +
"where ph.person = pr and ph is not null",
Object[].class)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select distinct pr1 " +
"from Person pr1, Person pr2 " +
"where pr1.id <> pr2.id " +
" and pr1.address = pr2.address " +
" and pr1.createdOn < pr2.createdOn",
Person.class)
.getResultList();
The previous queries may even be written using the syntax cross join
in place of the comma:
List<Object[]> persons = entityManager.createQuery(
"select distinct pr, ph " +
"from Person pr cross join Phone ph " +
"where ph.person = pr and ph is not null",
Object[].class)
.getResultList();
16.7.3. Polymorphism
HQL and JPQL queries are inherently polymorphic.
Consider:
List<Payment> payments = entityManager.createQuery(
"select p " +
"from Payment p ",
Payment.class)
.getResultList();
This query names the Payment
entity explicitly.
But the CreditCardPayment
and WireTransferPayment
entities inherit Payment
, and so p
ranges over all three types.
Instances of all these entities are returned by the query.
The query It returns every object of every mapped entity type. |
This behavior may be slightly adjusted using the @Polymorphism
annotation.
See Implicit and explicit polymorphism for more.
16.7.4. Derived roots
A derived root is an uncorrelated subquery which occurs in the from
clause.
It must declare an identification variable.
List<Tuple> calls = entityManager.createQuery(
"select d.owner, d.payed " +
"from (" +
" select p.person as owner, c.payment is not null as payed " +
" from Call c " +
" join c.phone p " +
" where p.number = :phoneNumber) d",
Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();
This feature can be used to break a more complicated query into smaller pieces.
We emphasize that a derived root must be an uncorrelated subquery. |
A subquery may also occur in a join, in which case it may be a correlated subquery.
16.7.5. Common table expressions in from
clause
A Common table expression (CTE) is like a derived root with a name. The big difference is,
that the name can be referred to multiple times. It must declare an identification variable.
The CTE name can be used for a from
clause root or a join
, similar to entity names.
Refer to the with clause chapter for details about CTEs.
16.8. Declaring joined entities
Joins allow us to navigate from one entity to another, via its associations, or via explicit join conditions.
There are:
-
explicit joins, declared within the
from
clause using the keywordjoin
, and -
implicit joins, which don’t need to be declared in the
from
clause.
An explicit join may be either:
-
an inner join, written as
join
orinner join
, -
a left outer join, written as
left join
orleft outer join
, -
a right outer join, written as
right join
orright outer join
, or -
a full outer join, written as
full join
orfull outer join
.
16.8.1. Explicit root joins
An explicit root join works just like an ANSI-style join in SQL.
List<Person> persons = entityManager.createQuery(
"select distinct pr " +
"from Person pr " +
"join Phone ph on ph.person = pr " +
"where ph.type = :phoneType",
Person.class)
.setParameter("phoneType", PhoneType.MOBILE)
.getResultList();
This looks nice and familiar, but it’s not the most common sort of join in HQL or JPQL. |
16.8.2. Explicit association joins
Every explicit association join specifies an entity attribute to be joined.
The specified attribute:
-
is usually a
@OneToMany
,@ManyToMany
,@OneToOne
, or@ManyToOne
association, but -
it could be an
@ElementCollection
, and -
it might even be an attribute of embeddable type.
In the case of an association or collection, the generated SQL will have a join of the same type.
(For a many-to-many association it will have two joins.)
In the case of an embedded attribute, the join is purely logical and does not result in a join in the generated SQL.
An explicit join may assign an identification variable to the joined entity.
List<Person> persons = entityManager.createQuery(
"select distinct pr " +
"from Person pr " +
"join pr.phones ph " +
"where ph.type = :phoneType",
Person.class)
.setParameter("phoneType", PhoneType.MOBILE)
.getResultList();
// same query, but specifying join type as 'inner' explicitly
List<Person> persons = entityManager.createQuery(
"select distinct pr " +
"from Person pr " +
"inner join pr.phones ph " +
"where ph.type = :phoneType",
Person.class)
.setParameter("phoneType", PhoneType.MOBILE)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select distinct pr " +
"from Person pr " +
"left join pr.phones ph " +
"where ph is null " +
" or ph.type = :phoneType",
Person.class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();
// same query, but specifying join type as 'outer' explicitly
List<Person> persons = entityManager.createQuery(
"select distinct pr " +
"from Person pr " +
"left outer join pr.phones ph " +
"where ph is null " +
" or ph.type = :phoneType",
Person.class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();
For further information about collection-valued association references, see Joining collections and many-valued associations.
16.8.3. Explicit association joins with join conditions
The with
or on
clause allows explicit qualification of the join conditions.
The specified join conditions are added to the join conditions specified by the foreign key association. The |
Join conditions occurring in the with
or on
clause are added to the on
clause in the generated SQL.
List<Object[]> personsAndPhones = session.createQuery(
"select pr.name, ph.number " +
"from Person pr " +
"left join pr.phones ph with ph.type = :phoneType ",
Object[].class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();
The following query is arguably less clear, but semantically equivalent:
List<Object[]> personsAndPhones = entityManager.createQuery(
"select pr.name, ph.number " +
"from Person pr " +
"left join pr.phones ph on ph.type = :phoneType ",
Object[].class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();
16.8.4. join fetch
for association fetching
A fetch join overrides the laziness of a given association, specifying that the association should be fetched with a SQL join.
The join may be an inner or outer join.
-
A
join fetch
, or, more explicitly,inner join fetch
, only returns base entities with an associated entity. -
A
left join fetch
, or—for lovers of verbosity—left outer join fetch
, returns all the base entities, including those which have no associated joined entity.
This is one of the most important features of Hibernate. |
For example, if Person
has a one-to-many association named phones
, the use of join fetch
in the following query specifies that the collection elements should be fetched in the same SQL query:
List<Person> persons = entityManager.createQuery(
"select distinct pr " +
"from Person pr " +
"left join fetch pr.phones ",
Person.class)
.getResultList();
In this example, we used a left outer join because we also wanted to obtain customers with no orders.
A query may have more than one fetch join, but be aware that:
-
it’s perfectly safe to fetch several to-one associations in series or parallel in a single query, and
-
a single series of nested fetch joins is also fine, but
-
fetching multiple collections or to-many associations in parallel results in a Cartesian product at the database level, and might exhibit very poor performance.
HQL doesn’t disallow it, but it’s usually a bad idea to apply a restriction to a join fetch
ed entity, since the elements of the fetched collection would be incomplete.
Indeed, it’s best to avoid even assigning an identification variable to a fetched joined entity except for the purpose of specifying a nested fetch join.
Fetch joins should usually be avoided in limited or paged queries.
Nor should they be used with the |
Fetch joins are disallowed in subqueries, where they would make no sense.
16.8.5. Joins with typecasts
An explicit join may narrow the type of the joined entity using treat()
.
// a to-many association
List<Object[]> payments = entityManager.createQuery(
"select a, ccp " +
"from Account a " +
"join treat(a.payments as CreditCardPayment) ccp " +
"where length(ccp.cardNumber) between 16 and 20",
Object[].class)
.getResultList();
// a to-one association
List<Object[]> payments = entityManager.createQuery(
"select c, ccp " +
"from Call c " +
"join treat(c.payment as CreditCardPayment) ccp " +
"where length(ccp.cardNumber) between 16 and 20",
Object[].class)
.getResultList();
Here, the identification variable ccp
declared to the right of treat()
has the narrowed type CreditCardPayment
, instead of the declared type Payment
.
This allows the attribute cardNumber
declared by the subtype CreditCardPayment
to be referenced in the rest of the query.
See Types and typecasts for more information about treat()
.
16.8.6. Subqueries in joins
A join
clause may contain a subquery, either:
-
an uncorrelated subquery, which is almost the same as a derived root, except that it may have an
on
restriction, or -
a lateral join, which is a correlated subquery, and may refer to other roots declared earlier in the same
from
clause.
The lateral
keyword just distinguishes the two cases.
List<Tuple> calls1 = entityManager.createQuery(
"from Phone p " +
"left join (" +
" select c.duration as duration, c.phone.id as cid" +
" from Call c" +
" order by c.duration desc" +
" limit 1" +
" ) as longest on cid = p.id " +
"where p.number = :phoneNumber " +
"select longest.duration",
Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();
//same, but using 'join lateral' instead of 'on'
List<Tuple> calls2 = entityManager.createQuery(
"from Phone p " +
"left join lateral (" +
" select c.duration as duration" +
" from p.calls c" +
" order by c.duration desc" +
" limit 1" +
" ) as longest " +
"where p.number = :phoneNumber " +
"select longest.duration",
Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();
A lateral join may be an inner or left outer join, but not a right join, nor a full join.
Traditional SQL doesn’t allow correlated subqueries in the On some databases, It’s almost as if they’re deliberately trying to confuse us. |
Lateral joins are particularly useful for computing top-N elements of multiple groups.
Most databases support some flavor of |
16.8.7. Implicit association joins (path expressions)
It’s not necessary to explicitly join
every entity that occurs in a query.
Instead, entity associations may be navigated, just like in Java:
-
if an attribute is of embedded type, or is a to-one association, it may be further navigated, but
-
if an attribute is of basic type, is collection-valued, or is a to-many association, it is considered terminal, and may not be further navigated.
It’s clear that:
-
A path expression like
p.name
with only two elements just refers to state held directly by an entity with an aliasp
defined infrom
orjoin
. -
But a longer path expression, for example,
ph.person.name
, might refer to state held by an associated entity.
(Alternatively, it might refer to state held by an embedded class.)
In the second case, Hibernate with automatically add a join to the generated SQL if necessary.
List<Phone> phones = entityManager.createQuery(
"select ph " +
"from Phone ph " +
"where ph.person.address = :address ",
Phone.class)
.setParameter("address", address)
.getResultList();
// same as
List<Phone> phones = entityManager.createQuery(
"select ph " +
"from Phone ph " +
"join ph.person pr " +
"where pr.address = :address ",
Phone.class)
.setParameter("address", address)
.getResultList();
As in this example, implicit joins usually appear outside the from
clause of the HQL query.
However, they always affect the from
clause of the SQL query.
Note that:
-
Implicit joins are always treated as inner joins.
-
Multiple occurrences of the same implicit join always refer to the same SQL join.
List<Phone> phones = entityManager.createQuery(
"select ph " +
"from Phone ph " +
"where ph.person.address = :address " +
" and ph.person.createdOn > :timestamp",
Phone.class)
.setParameter("address", address)
.setParameter("timestamp", timestamp)
.getResultList();
//same as
List<Phone> phones = entityManager.createQuery(
"select ph " +
"from Phone ph " +
"inner join ph.person pr " +
"where pr.address = :address " +
" and pr.createdOn > :timestamp",
Phone.class)
.setParameter("address", address)
.setParameter("timestamp", timestamp)
.getResultList();
16.8.8. Joining collections and many-valued associations
When a join involves a collection or many-valued association, the declared identification variable refers to the elements of the collection, that is:
-
to the elements of a
Set
, -
to the elements of a
List
, not to their indices in the list, or -
to the values of a
Map
, not to their keys.
List<Phone> phones = entityManager.createQuery(
"select ph " +
"from Person pr " +
"join pr.phones ph " +
"join ph.calls c " +
"where pr.address = :address " +
" and c.duration > :duration",
Phone.class)
.setParameter("address", address)
.setParameter("duration", duration)
.getResultList();
In this example, the identification variable ph
is of type Phone
, the element type of the list Person#phones
.
But if we need to refer to the index of a Phone
in the list, we need some extra syntax.
You might recall that we mentioned element()
and index()
and key()
, value()
, and entry()
a bit earlier.
These functions may be applied to the identification variable declared in a collection join or many-valued association join.
Function | Applies to | Interpretation | Notes |
---|---|---|---|
|
Any collection |
The collection element or map entry value |
Often optional. |
|
Any |
The index of the element in the list |
For backward compatibility, it’s also an alternative to |
|
Any |
The key of the entry in the list |
If the key is of entity type, it may be further navigated. |
|
Any |
The map entry, that is, the |
Only legal as a terminal path, and only allowed in the |
In particular, index()
and key()
obtain a reference to a list index or map key.
@OneToMany(mappedBy = "phone")
@MapKey(name = "timestamp")
private Map<LocalDateTime, Call> callHistory = new HashMap<>();
// select all the calls (the map value) for a given Phone
// note that here we don't need to use value() or element()
// since it is implicit
List<Call> calls = entityManager.createQuery(
"select ch " +
"from Phone ph " +
"join ph.callHistory ch " +
"where ph.id = :id ",
Call.class)
.setParameter("id", id)
.getResultList();
// same as above, but with value() explicit
List<Call> calls = entityManager.createQuery(
"select value(ch) " +
"from Phone ph " +
"join ph.callHistory ch " +
"where ph.id = :id ",
Call.class)
.setParameter("id", id)
.getResultList();
// select all the Call timestamps (the map key) for a given Phone
// note that here we *do* need to explicitly specify key()
List<LocalDateTime> timestamps = entityManager.createQuery(
"select key(ch) " +
"from Phone ph " +
"join ph.callHistory ch " +
"where ph.id = :id ",
LocalDateTime.class)
.setParameter("id", id)
.getResultList();
// select all the Call and their timestamps (the 'Map.Entry') for a given Phone
List<Map.Entry<Date, Call>> callHistory = entityManager.createQuery(
"select entry(ch) " +
"from Phone ph " +
"join ph.callHistory ch " +
"where ph.id = :id ")
.setParameter("id", id)
.getResultList();
// Sum all call durations for a given Phone of a specific Person
Long duration = entityManager.createQuery(
"select sum(ch.duration) " +
"from Person pr " +
"join pr.phones ph " +
"join ph.callHistory ch " +
"where ph.id = :id " +
" and index(ph) = :phoneIndex",
Long.class)
.setParameter("id", id)
.setParameter("phoneIndex", phoneIndex)
.getSingleResult();
16.8.9. Implicit joins involving collections
The functions element()
, index()
, key()
, and value()
may even be applied to a path expression to express an implicit join.
// implicit join to a map value()
List<Call> calls = entityManager.createQuery(
"select value(ph.callHistory) " +
"from Phone ph " +
"where ph.id = :id ",
Call.class)
.setParameter("id", id)
.getResultList();
// implicit join to a map key()
List<LocalDateTime> timestamps = entityManager.createQuery(
"select key(ph.callHistory) " +
"from Phone ph " +
"where ph.id = :id ",
LocalDateTime.class)
.setParameter("id", id)
.getResultList();
An element of an indexed collection (an array, list, or map) may even be identified using the index operator:
// indexed lists
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.phones[0].type = LAND_LINE",
Person.class)
.getResultList();
// maps
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where p.addresses['HOME'] = :address",
Person.class)
.setParameter("address", address)
.getResultList();
//max index in list
List<Person> persons = entityManager.createQuery(
"select pr " +
"from Person pr " +
"where pr.phones[max(indices(pr.phones))].type = 'LAND_LINE'",
Person.class)
.getResultList();
16.9. Projection: select
The select
list identifies which objects and values to return as the query results.
This operation is called projection. |
Any of the expression types discussed in Expressions may occur in the projection list, unless otherwise noted.
If a query has no explicit select list, the projection is inferred from the entities and joins occurring in the from clause, together with the result type specified by the call to createQuery() .It’s better to specify the projection explicitly, except in the simplest cases. |
There might be multiple items in a projection list, in which case each query result is a tuple, and this poses a problem:
Java doesn’t have a good way to represent tuples.
If there’s just one projected item in the select
list, then, no sweat, that’s the type of each query result.
There’s no need to bother with trying to represent a «tuple of length 1».
But if there are multiple expressions in the select list then:
-
by default, each query result is packaged as an array of type
Object[]
, or -
if explicitly requested by passing the class
Tuple
tocreateQuery()
, the query result is packaged as an instance ofjakarta.persistence.Tuple
.
List<Object[]> results = entityManager.createQuery(
"select p.name, p.nickName " +
"from Person p ",
Object[].class
).getResultList();
for (Object[] result : results) {
String name = (String) result[0];
String nickName = (String) result[1];
}
List<Tuple> tuples = entityManager.createQuery(
"select p.name as name, p.nickName as nickName " +
"from Person p ",
Tuple.class
).getResultList();
for (Tuple tuple : tuples) {
String name = tuple.get("name", String.class);
String nickName = tuple.get("nickName", String.class);
}
The names of the Tuple
elements are determined by the aliases given to the projected items in the select list.
If no aliases are specified, the elements may be accessed by their position in the list (positions are numbered from 0).
Unfortunately, neither Object[]
nor Tuple
lets us access an individual item in a result tuple of an HQL query without explicitly specifying the type of the item.
(Using a typecast in the case of Object[]
, or by passing the class object to get()
in the case of Tuple
.)
But there’s another option, as we’re about to see.
Simplifying slightly, the BNF for a projected item is:
(expression | instantiation) alias?
instantiation
: "NEW" instantiationTarget "(" instantiationArguments ")"
alias
: "AS"? IDENTIFIER
where instantiatiationArgs
is essentially a nested projection list.
So there’s a special expression type that’s only legal in the select clause: the instantiation
rule in the BNF above.
Let’s see what it does.
16.9.1. select new
The select new
construct packages the query results into a user-written Java class instead of an array.
public class CallStatistics {
private final long count;
private final long total;
private final int min;
private final int max;
private final double avg;
public CallStatistics(long count, long total, int min, int max, double avg) {
this.count = count;
this.total = total;
this.min = min;
this.max = max;
this.avg = avg;
}
//Getters and setters omitted for brevity
}
CallStatistics callStatistics = entityManager.createQuery(
"select new org.hibernate.orm.test.hql.CallStatistics(" +
" count(c), " +
" sum(c.duration), " +
" min(c.duration), " +
" max(c.duration), " +
" avg(c.duration)" +
") " +
"from Call c ",
CallStatistics.class)
.getSingleResult();
The class must be specified by its fully qualified name, and it must have a matching constructor.
This class does not need to be mapped or annotated in any way. Even if the class is an entity class, the resulting instances are not managed entities and are not associated with the session. |
Alternatively, using the syntax select new map
, the query may specify that each result should be packaged as a map:
List<Map> phoneCallTotalDurations = entityManager.createQuery(
"select new map(" +
" p.number as phoneNumber , " +
" sum(c.duration) as totalDuration, " +
" avg(c.duration) as averageDuration " +
") " +
"from Call c " +
"join c.phone p " +
"group by p.number ",
Map.class)
.getResultList();
The keys of the map are determined by the aliases given to the projected items in the select list.
If no aliases are specified, the key of an item is its position in the list (positions are numbered from 0).
Or, using the syntax select new list
, the query may specify that each result should be packaged as a list:
List<List> phoneCallDurations = entityManager.createQuery(
"select new list(" +
" p.number, " +
" c.duration " +
") " +
"from Call c " +
"join c.phone p ",
List.class)
.getResultList();
This is an older syntax, that predates JPQL. |
16.9.2. distinct
The distinct
keyword helps remove duplicate results from the query result list.
It’s only effect is to add distinct
to the generated SQL.
List<String> lastNames = entityManager.createQuery(
"select distinct p.lastName " +
"from Person p", String.class)
.getResultList();
As of Hibernate 6, duplicate results arising from the use of |
16.9.3. Aggregate functions
It’s common to have aggregate functions like count()
, sum()
, and max()
in a select list.
Aggregate functions are special functions that reduce the size of the result set.
The standard aggregate functions defined in both ANSI SQL and JPQL are:
Aggregate function | Argument type | Result type | JPA standard / ANSI SQL standard |
---|---|---|---|
|
Any |
|
✓/✓ |
|
Any numeric type |
|
✓/✓ |
|
Any numeric type, or string |
Same as the argument type |
✓/✓ |
|
Any numeric type, or string |
Same as the argument type |
✓/✓ |
|
Any numeric type |
See table below |
✓/✓ |
|
Any numeric type |
|
✗/✓ |
|
Any numeric type |
|
✗/✓ |
In the case of sum()
, the rules for assigning a result type are:
Argument type | Result type |
---|---|
Any integral numeric type except |
|
Any floating point numeric type |
|
|
|
|
|
There are also ordered set aggregate functions.
Object[] callStatistics = entityManager.createQuery(
"select " +
" count(c), " +
" sum(c.duration), " +
" min(c.duration), " +
" max(c.duration), " +
" avg(c.duration) " +
"from Call c ",
Object[].class)
.getSingleResult();
Long phoneCount = entityManager.createQuery(
"select count(distinct c.phone) " +
"from Call c ",
Long.class)
.getSingleResult();
List<Object[]> callCount = entityManager.createQuery(
"select p.number, count(c) " +
"from Call c " +
"join c.phone p " +
"group by p.number",
Object[].class)
.getResultList();
HQL defines the two additional aggregate functions which accept a logical predicate as an argument, for example, every(p.amount < 1000.0)
.
Aggregate function | Argument type | Result type | JPA standard |
---|---|---|---|
|
Logical predicate |
|
✗ |
|
Logical predicate |
|
✗ |
Aggregate functions usually appear in the select clause, but control over aggregation is the responsibility of the group by clause, as described below.
|
16.9.4. Aggregate functions and collections
The elements()
and indices()
functions we met earlier let us apply aggregate functions to a collection:
New syntax | Legacy HQL function | Applies to | Purpose |
---|---|---|---|
|
|
Any collection with sortable elements |
The maximum element or map value |
|
|
Any collection with sortable elements |
The minimum element or map value |
|
— |
Any collection with numeric elements |
The sum of the elements or map values |
|
— |
Any collection with numeric elements |
The average of the elements or map values |
|
|
Indexed collections (lists and maps) |
The maximum list index or map key |
|
|
Indexed collections (lists and maps) |
The minimum list index or map key |
|
— |
Indexed collections (lists and maps) |
The sum of the list indexes or map keys |
|
— |
Indexed collections (lists and maps) |
The average of the list indexes or map keys |
List<Phone> phones = entityManager.createQuery(
"select p " +
"from Phone p " +
"where max(elements(p.calls)) = :call",
Phone.class)
.setParameter("call", call)
.getResultList();
List<Phone> phones = entityManager.createQuery(
"select p " +
"from Phone p " +
"where min(elements(p.calls)) = :call",
Phone.class)
.setParameter("call", call)
.getResultList();
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"where max(indices(p.phones)) = 0",
Person.class)
.getResultList();
These operations can almost always be written in another way, without the use of these convenience functions. |
16.9.5. filter
All aggregate functions support the inclusion of a filter clause, a sort of mini-where
applying a restriction to just one item of the select list:
List<Long> callCount = entityManager.createQuery(
"select count(c) filter (where c.duration < 30) " +
"from Call c ",
Long.class)
.getResultList();
List<Object[]> callCount = entityManager.createQuery(
"select p.number, count(c) filter (where c.duration < 30) " +
"from Call c " +
"join c.phone p " +
"group by p.number",
Object[].class)
.getResultList();
16.9.6. Ordered set aggregate functions: within group
An ordered set aggregate function is a special aggregate function which has:
-
not only an optional filter clause, as above, but also
-
a
within group
clause containing a mini-order by
specification.
There are two main types of ordered set aggregate function:
-
an inverse distribution function calculates a value that characterizes the distribution of values within the group, for example,
percentile_cont(0.5)
is the median, andpercentile_cont(0.25)
is the lower quartile. -
a hypothetical set function determines the position of a «hypothetical» value within the ordered set of values.
The following ordered set aggregate functions are available on many platforms:
Type | Functions |
---|---|
Inverse distribution functions |
|
Hypothetical set functions |
|
Other |
|
Actually, the most widely-supported ordered set aggregate function is one which builds a string by concatenating the values within a group.
This function has different names on different databases, but HQL abstracts these differences, and—following ANSI SQL—calls it listagg()
.
List<String> callCount = entityManager.createQuery(
"select listagg(p.number, ', ') within group (order by p.type,p.number) " +
"from Phone p " +
"group by p.person",
String.class)
.getResultList();
16.9.7. Window functions: over
A window function is one which also has an over
clause, which may specify:
-
window frame partitioning, with
partition by
, which is very similar togroup by
, -
ordering, with
order by
, which defines the order of rows within a window frame, and/or -
windowing, with
range
,rows
, orgroups
, which define the bounds of the window frame within a partition.
The default partitioning and ordering is taken from the group by
and order by
clauses of the query.
Every partition runs in isolation, that is, rows can’t leak across partitions.
Like ordered set aggregate functions, window functions may optionally specify filter
or within group
.
Window functions are similar to aggregate functions in the sense that they compute some value based on a «frame» comprising multiple rows.
But unlike aggregate functions, window functions don’t flatten rows within a window frame.
The windowing clause specifies one of the following modes:
-
rows
for frame start/end defined by a set number of rows, for example,rows n preceding
means that onlyn
preceding rows are part of a frame, -
range
for frame start/end defined by value offsets, for example,range n preceding
means a preceding row is part of a frame if theabs(value, lag(value) over(..)) ⇐ N
, or -
groups
for frame start/end defined by group offsets, for example,groups n preceding
meansn
preceding peer groups are part of a frame, a peer group being rows with equivalent values fororder by
expressions.
The frame exclusion clause allows excluding rows around the current row:
-
exclude current row
excludes the current row, -
exclude group
excludes rows of the peer group of the current row, -
exclude ties
excludes rows of the peer group of the current row, except the current row, and -
exclude no others
is the default, and does not exclude anything.
Frame clause modes range and groups , as well as frame exclusion modes might not be available on every database.
|
The default frame is rows between unbounded preceding and current row exclude no others
,
which means that all rows prior to the «current row» are considered.
The following window functions are available on all major platforms:
Window function | Purpose | Signature |
---|---|---|
|
The position of the current row within its frame |
|
|
The value of a subsequent row in the frame |
|
|
The value of a previous row in the frame |
|
|
The value of a first row in the frame |
|
|
The value of a last row in the frame |
|
|
The value of the `n`th row in the frame |
|
In principle every aggregate or ordered set aggregate function might also be used as a window function, just by specifying over
, but not every function is supported on every database.
Window functions and ordered set aggregate functions aren’t available on every database. |
16.10. Restriction: where
The where
clause restricts the results returned by a select
query or limits the scope of an update
or delete
query.
This operation is usually called selection, but since that term is often confused with the select keyword, and since both projection and selection involve «selecting» things, here we’ll use the less-ambiguous term restriction.
|
A restriction is nothing more than a single logical expression, a topic we exhausted above in Predicates.
16.11. Aggregation: group by
and having
An aggregate query is one with aggregate functions in its projection list.
The group by
clause divides the result set into groups, so that a query with aggregate functions in the select list returns not a single result for the whole query, but one result for each group.
In short, grouping controls the effect of aggregation. |
A query with aggregation may also have a having
clause, a restriction applied to the groups.
16.11.1. Aggregation and grouping: group by
The group by
clause looks quite similar to the select
clause—it has a list of grouped items, but:
-
if there’s just one item, then the query will have a single result for each unique value of that item, or
-
if there are multiple items, the query will have a result for each unique combination or their values.
The BNF for a grouped item is just:
identifier | INTEGER_LITERAL | expression
Consider the following queries:
Long totalDuration = entityManager.createQuery(
"select sum(c.duration) " +
"from Call c ",
Long.class)
.getSingleResult();
List<Object[]> personTotalCallDurations = entityManager.createQuery(
"select p.name, sum(c.duration) " +
"from Call c " +
"join c.phone ph " +
"join ph.person p " +
"group by p.name",
Object[].class)
.getResultList();
//It's even possible to group by entities!
List<Object[]> personTotalCallDurations = entityManager.createQuery(
"select p, sum(c.duration) " +
"from Call c " +
"join c.phone ph " +
"join ph.person p " +
"group by p",
Object[].class)
.getResultList();
The first query retrieves the complete total over all orders.
The second retrieves the total for each customer, after grouping the orders by customer.
16.11.2. Totals and subtotals: rollup
and cube
The special functions rollup()
and cube()
may be used in the group by
clause, when supported by the database.
The semantics are identical to SQL.
These functions are especially useful for reporting:
-
A
group by
clause withrollup()
is used to produce subtotals and grand totals. -
A
group by
clause withcube()
allows totals for every combination of columns.
16.11.3. Aggregation and restriction: having
In a grouped query, the where
clause applies to the non-aggregated values (it determines which rows will make it into the aggregation).
The having
clause also restricts results, but it operates on the aggregated values.
In an example above, we retrieved Call
duration totals for all persons.
If that ended up being too much data to deal with, we might want to restrict the results to focus only on customers with a summed total of more than 1000:
List<Object[]> personTotalCallDurations = entityManager.createQuery(
"select p.name, sum(c.duration) " +
"from Call c " +
"join c.phone ph " +
"join ph.person p " +
"group by p.name " +
"having sum(c.duration) > 1000",
Object[].class)
.getResultList();
The having
clause follows the same rules as the where
clause and is also made up of predicates.
having
is applied after the groupings and aggregations have been done, while the where
clause is applied before.
16.12. Operations on result sets: union
, intersect
, and except
These operators apply not to expressions, but to entire result sets:
-
union
andunion all
, -
intersect
andintersect all
, and -
except
andexcept all
.
Just like in SQL, all
suppresses the elimination of duplicate results.
List<String> results = entityManager.createQuery(
"select p.name from Person p " +
"union " +
"select p.nickName from Person p where p.nickName is not null",
String.class
).getResultList();
16.13. Sorting: order by
By default, the results of the query are returned in an arbitrary order.
Imposing an order on a set is called sorting. A relation (a database table) is a set, and therefore certain particularly dogmatic purists have argued that sorting has no place in the algebra of relations. |
The order by
clause specifies a list of projected items used to sort the results.
Each sorted item may be:
-
an attribute of an entity or embeddable class,
-
a more complex expression,
-
the alias of a projected item declared in the select list, or
-
a literal integer indicating the ordinal position of a projected item in the select list.
Of course, in principle, only certain types may be sorted: numeric types, string, and date and time types.
But HQL is very permissive here and will allow an expression of almost any type to occur in a sort list.
Even the identification variable of an entity with a sortable identifier type may occur as a sorted item.
The JPQL specification requires that every sorted item in the Therefore, you might wish to avoid the use of complex expressions in the sort list. |
The BNF for a sorted item is:
sortExpression sortDirection? nullsPrecedence?
sortExpression
: identifier | INTEGER_LITERAL | expression
sortDirection
: "ASC" | "DESC"
nullsPrecedence
: "NULLS" ("FIRST" | "LAST")
Each sorted item listed in the order by
clause may explicitly specify a direction, either:
-
asc
for ascending order, or -
desc
for descending order.
If no direction is explicitly specified, the results are returned in ascending order.
Of course, there’s an ambiguity with respect to null values.
Therefore, the sorting of null values may also be explicitly specified:
-
nulls first
puts null values at the beginning of the result set, and -
nulls last
puts them last.
List<Person> persons = entityManager.createQuery(
"select p " +
"from Person p " +
"order by p.name",
Person.class)
.getResultList();
List<Object[]> personTotalCallDurations = entityManager.createQuery(
"select p.name, sum(c.duration) as total " +
"from Call c " +
"join c.phone ph " +
"join ph.person p " +
"group by p.name " +
"order by total",
Object[].class)
.getResultList();
Queries with an ordered result list may have limits or pagination.
16.13.1. Limits and offsets
It’s often useful to place a hard upper limit on the number of results that may be returned by a query.
The limit
and offset
clauses are an alternative to the use of setMaxResults()
and setFirstResult()
respectively,
and also may be used for Pagination and limits.
If the |
The SQL syntax fetch first … rows only
and fetch next … rows only
is also allowed.
The BNF is a bit complicated:
limitClause
: "LIMIT" parameterOrIntegerLiteral
offsetClause
: "OFFSET" parameterOrIntegerLiteral ("ROW" | "ROWS")?
fetchClause
: "FETCH" ("FIRST" | "NEXT")
(parameterOrIntegerLiteral | parameterOrNumberLiteral "%")
("ROW" | "ROWS")
("ONLY" | "WITH" "TIES")
These two queries are identical:
List<Call> calls1 = entityManager.createQuery(
"select c " +
"from Call c " +
"join c.phone p " +
"order by p.number " +
"limit 50",
Call.class)
.getResultList();
// same thing
List<Call> calls2 = entityManager.createQuery(
"select c " +
"from Call c " +
"join c.phone p " +
"order by p.number " +
"fetch first 50 rows only",
Call.class)
.getResultList();
These are well-defined limits: the number of results returned by the database will be limited to 50, as promised.
But not every query is quite so well-behaved.
Limiting certainly isn’t a well-defined relational operation, and must be used with care. In particular, limits don’t play well with fetch joins. |
This next query is accepted by HQL, and no more than 50 results are returned by getResultList()
, just as expected:
// don't do this! join fetch should not be used with limit
List<Phone> wrongCalls = entityManager.createQuery(
"select p " +
"from Phone p " +
"join fetch p.calls " +
"order by p " +
"limit 50",
Phone.class)
.getResultList();
However, if you log the SQL executed by Hibernate, you’ll notice something wrong:
select
p1_0.id,
c1_0.phone_id,
c1_0.calls_ORDER,
c1_0.id,
c1_0.duration,
c1_0.payment_id,
c1_0.call_timestamp,
p1_0.phone_number,
p1_0.person_id,
p1_0.phone_type
from
Phone p1_0
join
phone_call c1_0
on p1_0.id=c1_0.phone_id
order by 1
What happened to the limit
clause?
When limits or pagination are combined with a fetch join, Hibernate must retrieve all matching results from the database and apply the limit in memory! This almost certainly isn’t the behavior you were hoping for, and in general will exhibit terrible performance characteristics. |
In the next chapter we’ll see a completely different way to write queries in Hibernate.
16.13.2. With clause
The with
clause allows to specify common table expressions (CTEs) which can be imagined like named subqueries.
Every uncorrelated subquery can be factored to a CTE in the with
clause. The semantics are equivalent.
The with
clause offers features beyond naming subqueries though:
-
Specify materialization hints
-
Recursive querying
Materialization hint
The materialization hint MATERIALIZED
or NOT MATERIALIZED
can be applied to tell the DBMS whether a CTE should
or shouldn’t be materialized. Consult the database manual of the respective database for the exact meaning of the hint.
Usually, one can expect that MATERIALIZED
will cause the subquery to be executed separately and saved into a temporary table,
whereas NOT MATERIALIZED
will cause the subquery to be inlined into every use site and considered during optimizations separately.
List<Tuple> calls = entityManager.createQuery(
"with data as materialized(" +
" select p.person as owner, c.payment is not null as payed " +
" from Call c " +
" join c.phone p " +
" where p.number = :phoneNumber" +
")" +
"select d.owner, d.payed " +
"from data d",
Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();
Recursive querying
The main use case for the with
clause is to define a name for a subquery,
such that this subquery can refer to itself, which ultimately enables recursive querying.
Recursive CTEs must follow a very particular shape, which is
-
Base query part
-
union
orunion all
-
Recursive query part
List<Tuple> calls = entityManager.createQuery(
"with paymentConnectedPersons as(" +
" select a.owner owner " +
" from Account a where a.id = :startId " +
" union all" +
" select a2.owner owner " +
" from paymentConnectedPersons d " +
" join Account a on a.owner = d.owner " +
" join a.payments p " +
" join Account a2 on a2.owner = p.person" +
")" +
"select d.owner " +
"from paymentConnectedPersons d",
Tuple.class)
.setParameter("startId", 123L)
.getResultList();
The base query part represents the initial set of rows. When fetching a tree of data,
the base query part usually is the tree root.
The recursive query part is executed again and again until it produces no new rows.
The result of such a CTE is the base query part result unioned together with all recursive query part executions.
Depending on whether union all
or union
(distinct
) is used, duplicate rows are preserved or not.
Recursive queries additionally can have
-
a
search
clause to hint the DBMS whether to use breadth or depth first searching -
a
cycle
clause to hint the DBMS how to determine that a cycle was reached
Defining the search
clause requires specifying a name for an attribute in the set
sub-clause,
that will be added to the CTE type and allows ordering results according to the search order.
searchClause
: "SEARCH" ("BREADTH"|"DEPTH") "FIRST BY" searchSpecifications "SET" identifier
;
searchSpecifications
: searchSpecification ("," searchSpecification)*
;
searchSpecification
: identifier sortDirection? nullsPrecedence?
;
A DBMS has two possible orders when executing the recursive query part
-
Depth first — handle the newest produced rows by the recursive query part first
-
Breadth first — handle the oldest produced rows by the recursive query part first
List<Tuple> calls = entityManager.createQuery(
"with paymentConnectedPersons as(" +
" select a.owner owner " +
" from Account a where a.id = :startId " +
" union all" +
" select a2.owner owner " +
" from paymentConnectedPersons d " +
" join Account a on a.owner = d.owner " +
" join a.payments p " +
" join Account a2 on a2.owner = p.person" +
") search breadth first by owner set orderAttr " +
"select d.owner " +
"from paymentConnectedPersons d",
Tuple.class)
.setParameter("startId", 123L)
.getResultList();
Recursive processing can lead to cycles which might lead to queries executing forever.
The cycle
clause hints the DBMS which CTE attributes to track for the cycle detection.
It requires specifying a name for a cycle mark attribute in the set
sub-clause,
that will be added to the CTE type and allows detecting if a cycle occurred for a result.
By default, the cycle mark attribute will be set to true
when a cycle is detected and false
otherwise.
The values to use can be explicitly specified through the to
and default
sub-clauses.
Optionally, it’s also possible to specify a cycle path attribute name through the using
clause
The cycle path attribute can be used to understand the traversal path that lead to a result.
cycleClause
: "CYCLE" cteAttributes "SET" identifier ("TO" literal "DEFAULT" literal)? ("USING" identifier)?
;
List<Tuple> calls = entityManager.createQuery(
"with paymentConnectedPersons as(" +
" select a.owner owner " +
" from Account a where a.id = :startId " +
" union all" +
" select a2.owner owner " +
" from paymentConnectedPersons d " +
" join Account a on a.owner = d.owner " +
" join a.payments p " +
" join Account a2 on a2.owner = p.person" +
") cycle owner set cycleMark " +
"select d.owner, d.cycleMark " +
"from paymentConnectedPersons d",
Tuple.class)
.setParameter("startId", 123L)
.getResultList();
Hibernate merely translates recursive CTEs but doesn’t attempt to emulate the feature. Note that most modern database versions support recursive CTEs already. |
17. Criteria
Criteria queries offer a type-safe alternative to HQL, JPQL and native SQL queries.
Criteria queries are a programmatic, type-safe way to express a query.
They are type-safe in terms of using interfaces and classes to represent various structural parts of a query such as the query itself, the select clause, or an order-by, etc.
They can also be type-safe in terms of referencing attributes as we will see in a bit.
Users of the older Hibernate org.hibernate.Criteria
query API will recognize the general approach, though we believe the Jakarta Persistence API to be superior as it represents a clean look at the lessons learned from that API.
Criteria queries are essentially an object graph, where each part of the graph represents an increasing (as we navigate down this graph) more atomic part of the query.
The first step in performing a criteria query is building this graph.
The jakarta.persistence.criteria.CriteriaBuilder
interface is the first thing with which you need to become acquainted with before using criteria queries.
Its role is that of a factory for all the individual pieces of the criteria.
You obtain a jakarta.persistence.criteria.CriteriaBuilder
instance by calling the getCriteriaBuilder()
method of either jakarta.persistence.EntityManagerFactory
or jakarta.persistence.EntityManager
.
The next step is to obtain a jakarta.persistence.criteria.CriteriaQuery
.
This is accomplished using one of the three methods on jakarta.persistence.criteria.CriteriaBuilder
for this purpose:
-
<T> CriteriaQuery<T> createQuery( Class<T> resultClass )
-
CriteriaQuery<Tuple> createTupleQuery()
-
CriteriaQuery<Object> createQuery()
Each serves a different purpose depending on the expected type of the query results.
The chapter 6 (i.e., Criteria API) of the Jakarta Persistence Specification already contains a decent amount of reference material pertaining to the various parts of a criteria query. |
17.1. Typed criteria queries
The type of the criteria query (aka the <T>
) indicates the expected types in the query result.
This might be an entity, an Integer
, or any other object.
17.2. Selecting an entity
This is probably the most common form of query.
The application wants to select entity instances.
Example 553. Selecting the root entity
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Person> criteria = builder.createQuery(Person.class);
Root<Person> root = criteria.from(Person.class);
criteria.select(root);
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));
List<Person> persons = entityManager.createQuery(criteria).getResultList();
The example uses createQuery()
passing in the Person
class reference as the results of the query will be Person
objects.
The call to the The See Build Tool Integration for details on generating this static metamodel. |
17.3. Selecting an expression
The simplest form of selecting an expression is selecting a particular attribute from an entity.
But this expression might also represent an aggregation, a mathematical operation, etc.
Example 554. Selecting an attribute
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<String> criteria = builder.createQuery(String.class);
Root<Person> root = criteria.from(Person.class);
criteria.select(root.get(Person_.nickName));
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));
List<String> nickNames = entityManager.createQuery(criteria).getResultList();
In this example, the query is typed as java.lang.String
because that is the anticipated type of the results (the type of the Person#nickName
attribute is java.lang.String
).
Because a query might contain multiple references to the Person
entity, attribute references always need to be qualified.
This is accomplished by the Root#get
method call.
17.4. Selecting multiple values
There are actually a few different ways to select multiple values using criteria queries.
We will explore two options here, but an alternative recommended approach is to use tuples as described in Tuple criteria queries,
or consider a wrapper query, see Selecting a wrapper for details.
Example 555. Selecting an array
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Object[]> criteria = builder.createQuery(Object[].class);
Root<Person> root = criteria.from(Person.class);
Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);
criteria.select(builder.array(idPath, nickNamePath));
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));
List<Object[]> idAndNickNames = entityManager.createQuery(criteria).getResultList();
Technically this is classified as a typed query, but you can see from handling the results that this is sort of misleading.
Anyway, the expected result type here is an array.
The example then uses the array method of jakarta.persistence.criteria.CriteriaBuilder
which explicitly combines individual selections into a jakarta.persistence.criteria.CompoundSelection
.
Example 556. Selecting an array using multiselect
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Object[]> criteria = builder.createQuery(Object[].class);
Root<Person> root = criteria.from(Person.class);
Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);
criteria.multiselect(idPath, nickNamePath);
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));
List<Object[]> idAndNickNames = entityManager.createQuery(criteria).getResultList();
Just as we saw in Selecting an array we have a typed criteria query returning an Object
array.
Both queries are functionally equivalent.
This second example uses the multiselect()
method which behaves slightly differently based on the type given when the criteria query was first built,
but, in this case, it says to select and return an Object[].
17.5. Selecting a wrapper
Another alternative to Selecting multiple values is to instead select an object that will «wrap» the multiple values.
Going back to the example query there, rather than returning an array of [Person#id, Person#nickName], instead declare a class that holds these values and use that as a return object.
Example 557. Selecting a wrapper
public class PersonWrapper {
private final Long id;
private final String nickName;
public PersonWrapper(Long id, String nickName) {
this.id = id;
this.nickName = nickName;
}
public Long getId() {
return id;
}
public String getNickName() {
return nickName;
}
}
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<PersonWrapper> criteria = builder.createQuery(PersonWrapper.class);
Root<Person> root = criteria.from(Person.class);
Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);
criteria.select(builder.construct(PersonWrapper.class, idPath, nickNamePath));
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));
List<PersonWrapper> wrappers = entityManager.createQuery(criteria).getResultList();
First, we see the simple definition of the wrapper object we will be using to wrap our result values.
Specifically, notice the constructor and its argument types.
Since we will be returning PersonWrapper
objects, we use PersonWrapper
as the type of our criteria query.
This example illustrates the use of the jakarta.persistence.criteria.CriteriaBuilder
method construct which is used to build a wrapper expression.
For every row in the result, we are saying we would like a PersonWrapper
instantiated with the remaining arguments by the matching constructor.
This wrapper expression is then passed as the select.
17.6. Tuple criteria queries
A better approach to Selecting multiple values is to use either a wrapper (which we just saw in Selecting a wrapper) or using the jakarta.persistence.Tuple
contract.
Example 558. Selecting a tuple
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Tuple> criteria = builder.createQuery(Tuple.class);
Root<Person> root = criteria.from(Person.class);
Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);
criteria.multiselect(idPath, nickNamePath);
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));
List<Tuple> tuples = entityManager.createQuery(criteria).getResultList();
for (Tuple tuple : tuples) {
Long id = tuple.get(idPath);
String nickName = tuple.get(nickNamePath);
}
//or using indices
for (Tuple tuple : tuples) {
Long id = (Long) tuple.get(0);
String nickName = (String) tuple.get(1);
}
This example illustrates accessing the query results through the jakarta.persistence.Tuple
interface.
The example uses the explicit createTupleQuery()
of jakarta.persistence.criteria.CriteriaBuilder
.
An alternate approach is to use createQuery( Tuple.class )
.
Again we see the use of the multiselect()
method, just like in Selecting an array using multiselect
.
The difference here is that the type of the jakarta.persistence.criteria.CriteriaQuery
was defined as jakarta.persistence.Tuple
so the compound selections, in this case, are interpreted to be the tuple elements.
The jakarta.persistence.Tuple contract provides three forms of access to the underlying elements:
- typed
-
The Selecting a tuple example illustrates this form of access in the
tuple.get( idPath )
andtuple.get( nickNamePath )
calls.
This allows typed access to the underlying tuple values based on thejakarta.persistence.TupleElement
expressions used to build the criteria. - positional
-
Allows access to the underlying tuple values based on the position.
The simple Object get(int position) form is very similar to the access illustrated in Selecting an array and Selecting an array usingmultiselect
.
The <X> X get(int position, Class<X> type form allows typed positional access, but based on the explicitly supplied type which the tuple value must be type-assignable to. - aliased
-
Allows access to the underlying tuple values based on (optionally) assigned alias.
The example query did not apply an alias.
An alias would be applied via the alias method onjakarta.persistence.criteria.Selection
.
Just likepositional
access, there is both a typed (Object get(String alias)) and an untyped (<X> X get(String alias, Class<X> type)) form.
17.7. FROM clause
A CriteriaQuery
object defines a query over one or more entity, embeddable, or basic abstract schema types.
The root objects of the query are entities, from which the other types are reached by navigation.
— Java Persistence Specification, section 6.5.2 Query Roots, pg 262
All the individual parts of the FROM clause (roots, joins, paths) implement the |
17.8. Roots
Roots define the basis from which all joins, paths and attributes are available in the query.
A root is always an entity type. Roots are defined and added to the criteria by the overloaded from methods on jakarta.persistence.criteria.CriteriaQuery
:
Example 559. Root methods
<X> Root<X> from( Class<X> );
<X> Root<X> from( EntityType<X> );
Example 560. Adding a root example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Person> criteria = builder.createQuery(Person.class);
Root<Person> root = criteria.from(Person.class);
Criteria queries may define multiple roots, the effect of which is to create a Cartesian Product between the newly added root and the others.
Here is an example defining a Cartesian Product between Person
and Partner
entities:
Example 561. Adding multiple roots example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Tuple> criteria = builder.createQuery(Tuple.class);
Root<Person> personRoot = criteria.from(Person.class);
Root<Partner> partnerRoot = criteria.from(Partner.class);
criteria.multiselect(personRoot, partnerRoot);
Predicate personRestriction = builder.and(
builder.equal(personRoot.get(Person_.address), address),
builder.isNotEmpty(personRoot.get(Person_.phones))
);
Predicate partnerRestriction = builder.and(
builder.like(partnerRoot.get(Partner_.name), prefix),
builder.equal(partnerRoot.get(Partner_.version), 0)
);
criteria.where(builder.and(personRestriction, partnerRestriction));
List<Tuple> tuples = entityManager.createQuery(criteria).getResultList();
17.9. Joins
Joins allow navigation from other jakarta.persistence.criteria.From
to either association or embedded attributes.
Joins are created by the numerous overloaded join methods of the jakarta.persistence.criteria.From
interface.
Example 562. Join example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Phone> criteria = builder.createQuery(Phone.class);
Root<Phone> root = criteria.from(Phone.class);
// Phone.person is a @ManyToOne
Join<Phone, Person> personJoin = root.join(Phone_.person);
// Person.addresses is an @ElementCollection
Join<Person, String> addressesJoin = personJoin.join(Person_.addresses);
criteria.where(builder.isNotEmpty(root.get(Phone_.calls)));
List<Phone> phones = entityManager.createQuery(criteria).getResultList();
17.10. Fetches
Just like in HQL and JPQL, criteria queries can specify that associated data be fetched along with the owner.
Fetches are created by the numerous overloaded fetch methods of the jakarta.persistence.criteria.From
interface.
Example 563. Join fetch example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Phone> criteria = builder.createQuery(Phone.class);
Root<Phone> root = criteria.from(Phone.class);
// Phone.person is a @ManyToOne
Fetch<Phone, Person> personFetch = root.fetch(Phone_.person);
// Person.addresses is an @ElementCollection
Fetch<Person, String> addressesJoin = personFetch.fetch(Person_.addresses);
criteria.where(builder.isNotEmpty(root.get(Phone_.calls)));
List<Phone> phones = entityManager.createQuery(criteria).getResultList();
Technically speaking, embedded attributes are always fetched with their owner. |
17.11. Path expressions
Roots, joins and fetches are themselves path expressions as well. |
17.12. Using parameters
Example 564. Parameters example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Person> criteria = builder.createQuery(Person.class);
Root<Person> root = criteria.from(Person.class);
ParameterExpression<String> nickNameParameter = builder.parameter(String.class);
criteria.where(builder.equal(root.get(Person_.nickName), nickNameParameter));
TypedQuery<Person> query = entityManager.createQuery(criteria);
query.setParameter(nickNameParameter, "JD");
List<Person> persons = query.getResultList();
Use the parameter method of jakarta.persistence.criteria.CriteriaBuilder
to obtain a parameter reference.
Then use the parameter reference to bind the parameter value to the jakarta.persistence.Query
.
17.13. Using group by
Example 565. Group by example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Tuple> criteria = builder.createQuery(Tuple.class);
Root<Person> root = criteria.from(Person.class);
criteria.groupBy(root.get("address"));
criteria.multiselect(root.get("address"), builder.count(root));
List<Tuple> tuples = entityManager.createQuery(criteria).getResultList();
for (Tuple tuple : tuples) {
String name = (String) tuple.get(0);
Long count = (Long) tuple.get(1);
}
18. Native SQL Queries
You may also express queries in the native SQL dialect of your database.
This is useful if you want to utilize database-specific features such as window functions, Common Table Expressions (CTE) or the CONNECT BY
option in Oracle.
It also provides a clean migration path from a direct SQL/JDBC based application to Hibernate/Jakarta Persistence.
Hibernate also allows you to specify handwritten SQL (including stored procedures) for all create, update, delete, and retrieve operations.
18.1. Creating a native query using Jakarta Persistence
Execution of native SQL queries is controlled via the NativeQuery
interface, which is obtained by calling Session.createNativeQuery()
.
The following sections describe how to use this API for querying.
18.2. Scalar queries
The most basic SQL query is to get a list of scalars (column) values.
Example 566. Jakarta Persistence native query selecting all columns
List<Object[]> persons = entityManager.createNativeQuery(
"SELECT * FROM Person")
.getResultList();
Example 567. Jakarta Persistence native query with a custom column selection
List<Object[]> persons = entityManager.createNativeQuery(
"SELECT id, name FROM Person")
.getResultList();
for(Object[] person : persons) {
Number id = (Number) person[0];
String name = (String) person[1];
}
Example 568. Hibernate native query selecting all columns
List<Object[]> persons = session.createNativeQuery(
"SELECT * FROM Person", Object[].class)
.list();
Example 569. Hibernate native query with a custom column selection
List<Object[]> persons = session.createNativeQuery(
"SELECT id, name FROM Person", Object[].class)
.list();
for(Object[] person : persons) {
Number id = (Number) person[0];
String name = (String) person[1];
}
These will return a List
of Object
arrays ( Object[]
) with scalar values for each column in the PERSON
table.
Hibernate will use java.sql.ResultSetMetadata
to deduce the actual order and types of the returned scalar values.
To avoid the overhead of using ResultSetMetadata
, or simply to be more explicit in what is returned, one can use addScalar()
:
Example 570. Hibernate native query with explicit result set selection
List<Object[]> persons = session.createNativeQuery(
"SELECT * FROM Person", Object[].class)
.addScalar("id", StandardBasicTypes.LONG)
.addScalar("name", StandardBasicTypes.STRING)
.list();
for(Object[] person : persons) {
Long id = (Long) person[0];
String name = (String) person[1];
}
Although it still returns an Object
arrays, this query will not use the ResultSetMetadata
anymore since it explicitly gets the id
and name
columns as respectively a BigInteger
and a String
from the underlying ResultSet
.
This also means that only these two columns will be returned, even though the query is still using *
and the ResultSet
contains more than the three listed columns.
It is possible to leave out the type information for all or some of the scalars.
Example 571. Hibernate native query with result set selection that’s a partially explicit
List<Object[]> persons = session.createNativeQuery(
"SELECT * FROM Person", Object[].class)
.addScalar("id", StandardBasicTypes.LONG)
.addScalar("name")
.list();
for(Object[] person : persons) {
Long id = (Long) person[0];
String name = (String) person[1];
}
This is essentially the same query as before, but now ResultSetMetaData
is used to determine the type of name
, whereas the type of id
is explicitly specified.
How the java.sql.Types
returned from ResultSetMetaData
is mapped to Hibernate types is controlled by the Dialect
.
If a specific type is not mapped, or does not result in the expected type, it is possible to customize it via calls to registerHibernateType
in the Dialect.
18.3. Entity queries
The above queries were all about returning scalar values, basically returning the raw values from the ResultSet
.
Example 572. Jakarta Persistence native query selecting entities
List<Person> persons = entityManager.createNativeQuery(
"SELECT * FROM Person", Person.class)
.getResultList();
Example 573. Hibernate native query selecting entities
List<Person> persons = session.createNativeQuery(
"SELECT * FROM Person", Person.class)
.list();
Assuming that Person
is mapped as a class with the columns id
, name
, nickName
, address
, createdOn
, and version
,
the following query will also return a List
where each element is a Person
entity.
Example 574. Jakarta Persistence native query selecting entities with explicit result set
List<Person> persons = entityManager.createNativeQuery(
"SELECT id, name, nickName, address, createdOn, version " +
"FROM Person", Person.class)
.getResultList();
Example 575. Hibernate native query selecting entities with explicit result set
List<Person> persons = session.createNativeQuery(
"SELECT id, name, nickName, address, createdOn, version " +
"FROM Person", Person.class)
.list();
18.4. Handling associations and collections
If the entity is mapped with a many-to-one
or a child-side one-to-one
to another entity,
it is required to also return this when performing the native query,
otherwise, a database-specific column not found error will occur.
Example 576. Jakarta Persistence native query selecting entities with many-to-one association
List<Phone> phones = entityManager.createNativeQuery(
"SELECT id, phone_number, phone_type, person_id " +
"FROM Phone", Phone.class)
.getResultList();
Example 577. Hibernate native query selecting entities with many-to-one association
List<Phone> phones = session.createNativeQuery(
"SELECT id, phone_number, phone_type, person_id " +
"FROM Phone", Phone.class)
.list();
This will allow the Phone#person
to function properly since the many-to-one
or one-to-one
association is going to use a proxy that will be initialized when being navigated for the first time.
It is possible to eagerly join the Phone
and the Person
entities to avoid the possible extra roundtrip for initializing the many-to-one
association.
Example 578. Hibernate native query selecting entities with joined many-to-one association
List<Phone> tuples = session.createNativeQuery(
"SELECT {ph.*}, {pr.*} " +
"FROM Phone ph " +
"JOIN Person pr ON ph.person_id = pr.id", Phone.class, "ph")
.addJoin("pr", "ph.person")
.list();
for (Phone phone : tuples) {
assertNotNull(phone.getPerson().getName());
}
SELECT
*
FROM
Phone ph
JOIN
Person pr
ON ph.person_id = pr.id
As seen in the associated SQL query, Hibernate manages to construct the entity hierarchy without requiring any extra database roundtrip. |
Even when using the addJoin()
method, the result list will only contain the root entity.
Joined entities will only be present for their respective association.
Example 579. Hibernate native query selecting entities with joined many-to-one association and TupleTransformer
List<Phone> phones = session.createNativeQuery(
"SELECT {ph.*}, {pr.*} " +
"FROM Phone ph " +
"JOIN Person pr ON ph.person_id = pr.id", Phone.class, "ph")
.addJoin("pr", "ph.person")
.setTupleTransformer( (TupleTransformer<Phone>) (tuple, aliases) -> (Phone) tuple[0] )
.list();
for (Phone person : phones) {
person.getPerson();
}
Notice that you added an alias name pr to be able to specify the target property path of the join.
It is possible to do the same eager joining for collections (e.g. the Phone#calls
one-to-many
association).
Example 580. Jakarta Persistence native query selecting entities with joined one-to-many association
List<Phone> phones = entityManager.createNativeQuery(
"SELECT ph.* " +
"FROM Phone ph " +
"JOIN phone_call c ON c.phone_id = ph.id", Phone.class)
.getResultList();
for (Phone phone : phones) {
List<Call> calls = phone.getCalls();
}
SELECT *
FROM phone ph
JOIN call c ON c.phone_id = ph.id
Example 581. Hibernate native query selecting entities with joined one-to-many association
List<Phone> tuples = session.createNativeQuery(
"SELECT {ph.*}, {c.*} " +
"FROM Phone ph " +
"JOIN phone_call c ON c.phone_id = ph.id", Phone.class, "ph")
.addJoin("c", "ph.calls")
.list();
for (Phone phone : tuples) {
List<Call> calls = phone.getCalls();
}
SELECT *
FROM phone ph
JOIN call c ON c.phone_id = ph.id
At this stage, you are reaching the limits of what is possible with native queries, without starting to enhance the sql queries to make them usable in Hibernate.
Problems can arise when returning multiple entities of the same type or when the default alias/column names are not enough.
18.5. Returning multiple entities
Until now, the result set column names are assumed to be the same as the column names specified in the mapping document.
This can be problematic for SQL queries that join multiple tables since the same column names can appear in more than one table.
Column alias injection is needed in the following query which otherwise throws NonUniqueDiscoveredSqlAliasException
.
Example 582. Jakarta Persistence native query selecting entities with the same column names
List<Person> entities = entityManager.createNativeQuery(
"SELECT * " +
"FROM Person pr, Partner pt " +
"WHERE pr.name = pt.name", Person.class)
.getResultList();
Example 583. Hibernate native query selecting entities with the same column names
List<Person> entities = session.createNativeQuery(
"SELECT * " +
"FROM Person pr, Partner pt " +
"WHERE pr.name = pt.name", Person.class)
.list();
The query was intended to return all Person
and Partner
instances with the same name.
The query fails because there is a conflict of names since the two entities are mapped to the same column names (e.g. id
, name
, version
).
Also, on some databases, the returned column aliases will most likely be on the form pr.id
, pr.name
, etc.
which are not equal to the columns specified in the mappings (id
and name
).
The following form is not vulnerable to column name duplication:
Example 584. Hibernate native query selecting entities with the same column names and aliases
List<Object> entities = session.createNativeQuery(
"SELECT {pr.*}, {pt.*} " +
"FROM Person pr, Partner pt " +
"WHERE pr.name = pt.name", Object.class)
.addEntity("pr", Person.class)
.addEntity("pt", Partner.class)
.list();
There’s no such equivalent in Jakarta Persistence because the |
The {pr.}
and {pt.
}
notation used above is shorthand for «all properties».
Alternatively, you can list the columns explicitly, but even in this case, Hibernate injects the SQL column aliases for each property.
The placeholder for a column alias is just the property name qualified by the table alias.
18.6. Alias and property references
In most cases, the above alias injection is needed.
For queries relating to more complex mappings, like composite properties, inheritance discriminators, collections etc., you can use specific aliases that allow Hibernate to inject the proper aliases.
The following table shows the different ways you can use the alias injection.
Please note that the alias names in the result are simply examples, each alias will have a unique and probably different name when used.
Description | Syntax | Example |
---|---|---|
A simple property |
|
|
A composite property |
|
|
Discriminator of an entity |
|
|
All properties of an entity |
|
|
A collection key |
|
|
The id of a collection |
|
|
The element of a collection |
|
|
property of the element in the collection |
|
|
All properties of the element in the collection |
|
|
All properties of the collection |
|
|
18.7. Returning DTOs (Data Transfer Objects)
It is possible to apply a ResultTransformer
to native SQL queries, allowing it to return non-managed entities.
Example 585. Hibernate native query selecting DTOs
public class PersonSummaryDTO {
private Number id;
private String name;
//Getters and setters are omitted for brevity
public Number getId() {
return id;
}
public void setId(Number id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
List<PersonSummaryDTO> dtos = session.createNativeQuery(
"SELECT p.id as \"id\", p.name as \"name\" " +
"FROM Person p", Tuple.class)
.setTupleTransformer(
(tuple, aliases) -> {
PersonSummaryDTO dto = new PersonSummaryDTO();
dto.setId( (Long)tuple[0] );
dto.setName( (String)tuple[1] );
return dto;
}
)
.list();
There’s no such equivalent in Jakarta Persistence because the |
When materializing a native query result as a polymorphic entity, it is important to understand that both the The subclass id is determined based on some order and the base class of the entity hierarchy has the number 0. Refer to the respective sections in the inheritance chapter for examples of this. |
The above query will return a list of PersonSummaryDTO
which has been instantiated and injected the values of id
and name
into its corresponding properties or fields.
18.8. Handling inheritance
Native SQL queries which query for entities that are mapped as part of an inheritance must include all properties for the base class and all its subclasses.
Example 586. Hibernate native query selecting subclasses
List<CreditCardPayment> payments = session.createNativeQuery(
"SELECT * " +
"FROM Payment p " +
"JOIN CreditCardPayment cp on cp.id = p.id", CreditCardPayment.class)
.list();
There’s no such equivalent in Jakarta Persistence because the |
18.9. Parameters
Native SQL queries support ordinal as well as named parameters:
Example 587. Jakarta Persistence native query with parameters
List<Person> persons = entityManager.createNativeQuery(
"SELECT * " +
"FROM Person " +
"WHERE name like :name", Person.class)
.setParameter("name", "J%")
.getResultList();
Example 588. Hibernate native query with parameters
List<Person> persons = session.createNativeQuery(
"SELECT * " +
"FROM Person " +
"WHERE name like :name", Person.class)
.setParameter("name", "J%")
.list();
18.10. Named SQL queries
Named SQL queries can also be defined during mapping and called in exactly the same way as a named HQL query.
In this case, you do not need to call addEntity()
anymore.
Jakarta Persistence defines the jakarta.persistence.NamedNativeQuery
annotation for this purpose,
and the Hibernate org.hibernate.annotations.NamedNativeQuery
annotation extends it and adds the following attributes:
flushMode()
-
The flush mode for the query. By default, it uses the current Persistence Context flush mode.
cacheable()
-
Whether the query (results) is cacheable or not. By default, queries are not cached.
cacheRegion()
-
If the query results are cacheable, name the query cache region to use.
fetchSize()
-
The number of rows fetched by the JDBC Driver per database trip. The default value is given by the JDBC driver.
timeout()
-
The query timeout (in seconds). By default, there’s no timeout.
callable()
-
Does the SQL query represent a call to a procedure/function? The default is false.
comment()
-
A comment added to the SQL query for tuning the execution plan.
cacheMode()
-
The cache mode used for this query. This refers to entities/collections returned by the query.
The default value isCacheModeType.NORMAL
. readOnly()
-
Whether the results should be read-only. By default, queries are not read-only so entities are stored in the Persistence Context.
18.10.1. Named SQL queries selecting scalar values
To fetch a single column of given table, the named query looks as follows:
Example 589. Single scalar value NamedNativeQuery
@NamedNativeQuery(
name = "find_person_name",
query =
"SELECT name " +
"FROM Person ",
resultClass = String.class
)
Example 590. Jakarta Persistence named native query selecting a scalar value
List<String> names = entityManager.createNamedQuery(
"find_person_name", String.class)
.getResultList();
Example 591. Hibernate named native query selecting a scalar value
List<String> names = session.createNamedQuery(
"find_person_name", String.class)
.list();
Selecting multiple scalar values is done like this:
Example 592. Multiple scalar values NamedNativeQuery
@NamedNativeQuery(
name = "find_person_name_and_nickName",
query =
"SELECT " +
" name, " +
" nickName " +
"FROM Person "
)
Without specifying an explicit result type, Hibernate will assume an Object
array:
Example 593. Jakarta Persistence named native query selecting multiple scalar values
List<Object[]> tuples = entityManager.createNamedQuery(
"find_person_name_and_nickName", Object[].class)
.getResultList();
for(Object[] tuple : tuples) {
String name = (String) tuple[0];
String nickName = (String) tuple[1];
}
Example 594. Hibernate named native query selecting multiple scalar values
List<Object[]> tuples = session.createNamedQuery(
"find_person_name_and_nickName", Object[].class)
.list();
for(Object[] tuple : tuples) {
String name = (String) tuple[0];
String nickName = (String) tuple[1];
}
It’s possible to use a DTO to store the resulting scalar values:
Example 595. DTO to store multiple scalar values
public class PersonNames {
private final String name;
private final String nickName;
public PersonNames(String name, String nickName) {
this.name = name;
this.nickName = nickName;
}
public String getName() {
return name;
}
public String getNickName() {
return nickName;
}
}
Example 596. Multiple scalar values NamedNativeQuery
with ConstructorResult
@NamedNativeQuery(
name = "find_person_name_and_nickName_dto",
query =
"select " +
" name, " +
" nickName " +
"from Person ",
resultSetMapping = "name_and_nickName_dto"
)
@SqlResultSetMapping(
name = "name_and_nickName_dto",
classes = @ConstructorResult(
targetClass = PersonNames.class,
columns = {
@ColumnResult(name = "name"),
@ColumnResult(name = "nickName")
}
)
)
Example 597. Jakarta Persistence named native query selecting multiple scalar values into a DTO
List<PersonNames> personNames = entityManager.createNamedQuery(
"find_person_name_and_nickName_dto", PersonNames.class)
.getResultList();
Example 598. Hibernate named native query selecting multiple scalar values into a DTO
List<PersonNames> personNames = session.createNamedQuery(
"find_person_name_and_nickName_dto", PersonNames.class)
.list();
You can also use the @NamedNativeQuery
Hibernate annotation
to customize the named query using various configurations such as fetch mode, cacheability, time out interval.
Example 599. Multiple scalar values using ConstructorResult
and Hibernate NamedNativeQuery
@NamedNativeQuery(
name = "get_person_phone_count",
query = "select pr.name AS name, count(*) AS phoneCount " +
"from Phone p " +
"join Person pr ON pr.id = p.person_id " +
"group BY pr.name",
resultSetMapping = "person_phone_count",
timeout = 1,
readOnly = true
)
@SqlResultSetMapping(
name = "person_phone_count",
classes = @ConstructorResult(
targetClass = PersonPhoneCount.class,
columns = {
@ColumnResult(name = "name"),
@ColumnResult(name = "phoneCount")
}
)
)
Example 600. Hibernate NamedNativeQuery
named native query selecting multiple scalar values into a DTO
List<PersonPhoneCount> personNames = session.createNamedQuery(
"get_person_phone_count", PersonPhoneCount.class)
.getResultList();
18.10.2. Named SQL queries selecting entities
Considering the following named query:
Example 601. Single-entity NamedNativeQuery
@NamedNativeQuery(
name = "find_person_by_name",
query =
"select " +
" p.id AS \"id\", " +
" p.name AS \"name\", " +
" p.nickName AS \"nickName\", " +
" p.address AS \"address\", " +
" p.createdOn AS \"createdOn\", " +
" p.version AS \"version\" " +
"from Person p " +
"where p.name LIKE :name",
resultClass = Person.class
)
The result set mapping declares the entities retrieved by this native query.
Each field of the entity is bound to an SQL alias (or column name).
All fields of the entity including the ones of subclasses and the foreign key columns of related entities have to be present in the SQL query.
Field definitions are optional provided that they map to the same column name as the one declared on the class property.
Executing this named native query can be done as follows:
Example 602. Jakarta Persistence named native entity query
List<Person> persons = entityManager.createNamedQuery(
"find_person_by_name", Person.class)
.setParameter("name", "J%")
.getResultList();
Example 603. Hibernate named native entity query
List<Person> persons = session.createNamedQuery(
"find_person_by_name", Person.class)
.setParameter("name", "J%")
.list();
To join multiple entities, you need to use a SqlResultSetMapping
for each entity the SQL query is going to fetch.
Example 604. Joined-entities NamedNativeQuery
@NamedNativeQuery(
name = "find_person_with_phones_by_name",
query =
"select " +
" pr.id AS \"pr.id\", " +
" pr.name AS \"pr.name\", " +
" pr.nickName AS \"pr.nickName\", " +
" pr.address AS \"pr.address\", " +
" pr.createdOn AS \"pr.createdOn\", " +
" pr.version AS \"pr.version\", " +
" ph.id AS \"ph.id\", " +
" ph.person_id AS \"ph.person_id\", " +
" ph.phone_number AS \"ph.number\", " +
" ph.phone_type AS \"ph.type\" " +
"from Person pr " +
"join Phone ph ON pr.id = ph.person_id " +
"where pr.name LIKE :name",
resultSetMapping = "person_with_phones"
)
@SqlResultSetMapping(
name = "person_with_phones",
entities = {
@EntityResult(
entityClass = Person.class,
fields = {
@FieldResult( name = "id", column = "pr.id" ),
@FieldResult( name = "name", column = "pr.name" ),
@FieldResult( name = "nickName", column = "pr.nickName" ),
@FieldResult( name = "address", column = "pr.address" ),
@FieldResult( name = "createdOn", column = "pr.createdOn" ),
@FieldResult( name = "version", column = "pr.version" ),
}
),
@EntityResult(
entityClass = Phone.class,
fields = {
@FieldResult( name = "id", column = "ph.id" ),
@FieldResult( name = "person", column = "ph.person_id" ),
@FieldResult( name = "number", column = "ph.number" ),
@FieldResult( name = "type", column = "ph.type" ),
}
)
}
)
Example 605. Jakarta Persistence named native entity query with joined associations
List<Object[]> tuples = entityManager.createNamedQuery(
"find_person_with_phones_by_name", Object[].class)
.setParameter("name", "J%")
.getResultList();
for(Object[] tuple : tuples) {
Person person = (Person) tuple[0];
Phone phone = (Phone) tuple[1];
}
Example 606. Hibernate named native entity query with joined associations
List<Object[]> tuples = session.createNamedQuery(
"find_person_with_phones_by_name", Object[].class)
.setParameter("name", "J%")
.list();
for(Object[] tuple : tuples) {
Person person = (Person) tuple[0];
Phone phone = (Phone) tuple[1];
}
Finally, if the association to a related entity involves a composite primary key, a @FieldResult
element should be used for each foreign key column.
The @FieldResult
name is composed of the property name for the relationship, followed by a dot («.»), followed by the name or the field or property of the primary key.
For this example, the following entities are going to be used:
Example 607. Entity associations with composite keys and named native queries
@Embeddable
public class Dimensions {
private int length;
private int width;
//Getters and setters are omitted for brevity
}
@Embeddable
public class Identity implements Serializable {
private String firstname;
private String lastname;
//Getters and setters are omitted for brevity
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
final Identity identity = (Identity) o;
if (!firstname.equals(identity.firstname)) return false;
if (!lastname.equals(identity.lastname)) return false;
return true;
}
public int hashCode() {
int result;
result = firstname.hashCode();
result = 29 * result + lastname.hashCode();
return result;
}
}
@Entity
public class Captain {
@EmbeddedId
private Identity id;
//Getters and setters are omitted for brevity
}
@Entity
@NamedNativeQueries({
@NamedNativeQuery(name = "find_all_spaceships",
query =
"SELECT " +
" name as \"name\", " +
" model, " +
" speed, " +
" lname as lastn, " +
" fname as firstn, " +
" length, " +
" width, " +
" length * width as surface, " +
" length * width * 10 as volume " +
"FROM SpaceShip",
resultSetMapping = "spaceship"
)
})
@SqlResultSetMapping(
name = "spaceship",
entities = @EntityResult(
entityClass = SpaceShip.class,
fields = {
@FieldResult(name = "name", column = "name"),
@FieldResult(name = "model", column = "model"),
@FieldResult(name = "speed", column = "speed"),
@FieldResult(name = "captain.id.lastname", column = "lastn"),
@FieldResult(name = "captain.id.firstname", column = "firstn"),
@FieldResult(name = "dimensions.length", column = "length"),
@FieldResult(name = "dimensions.width", column = "width"),
}
),
columns = {
@ColumnResult(name = "surface"),
@ColumnResult(name = "volume")
}
)
public class SpaceShip {
@Id
private String name;
private String model;
private double speed;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "fname", referencedColumnName = "firstname")
@JoinColumn(name = "lname", referencedColumnName = "lastname")
private Captain captain;
private Dimensions dimensions;
//Getters and setters are omitted for brevity
}
Example 608. Jakarta Persistence named native entity query with joined associations and composite keys
List<Object[]> tuples = entityManager.createNamedQuery(
"find_all_spaceships", Object[].class)
.getResultList();
for(Object[] tuple : tuples) {
SpaceShip spaceShip = (SpaceShip) tuple[0];
Number surface = (Number) tuple[1];
Number volume = (Number) tuple[2];
}
Example 609. Hibernate named native entity query with joined associations and composite keys
List<Object[]> tuples = session.createNamedQuery(
"find_all_spaceships", Object[].class)
.list();
for(Object[] tuple : tuples) {
SpaceShip spaceShip = (SpaceShip) tuple[0];
Number surface = (Number) tuple[1];
Number volume = (Number) tuple[2];
}
18.11. Resolving global catalog and schema in native SQL queries
When using multiple database catalogs and schemas, Hibernate offers the possibility of
setting a global catalog or schema so that you don’t have to declare it explicitly for every entity.
Example 610. Setting global catalog and schema
<property name="hibernate.default_catalog" value="crm"/>
<property name="hibernate.default_schema" value="analytics"/>
This way, we can imply the global crm catalog and analytics schema in every JPQL, HQL or Criteria API query.
However, for native queries, the SQL query is passed as is, therefore you need to explicitly set the global catalog and schema whenever you are referencing a database table.
Fortunately, Hibernate allows you to resolve the current global catalog and schema using the following placeholders:
- {h-catalog}
-
resolves the current
hibernate.default_catalog
configuration property value. - {h-schema}
-
resolves the current
hibernate.default_schema
configuration property value. - {h-domain}
-
resolves the current
hibernate.default_catalog
andhibernate.default_schema
configuration property values (e.g. catalog.schema).
With these placeholders, you can imply the catalog, schema, or both catalog and schema for every native query.
So, when running the following native query:
@NamedNativeQuery(
name = "last_30_days_hires",
query =
"select * " +
"from {h-domain}person " +
"where age(hired_on) < '30 days'",
resultClass = Person.class
)
Hibernate is going to resolve the {h-domain}
placeholder according to the values of the default catalog and schema:
SELECT *
FROM crm.analytics.person
WHERE age(hired_on) < '30 days'
18.12. Using stored procedures for querying
Hibernate provides support for queries via stored procedures and functions.
A stored procedure arguments are declared using the IN
parameter type, and the result can be either marked with an OUT
parameter type, a REF_CURSOR
or it could just return the result like a function.
Example 611. MySQL stored procedure with OUT
parameter type
statement.executeUpdate(
"CREATE PROCEDURE sp_count_phones (" +
" IN personId INT, " +
" OUT phoneCount INT " +
") " +
"BEGIN " +
" SELECT COUNT(*) INTO phoneCount " +
" FROM Phone p " +
" WHERE p.person_id = personId; " +
"END"
);
To use this stored procedure, you can execute the following Jakarta Persistence query:
Example 612. Calling a MySQL stored procedure with OUT
parameter type using Jakarta Persistence
StoredProcedureQuery query = entityManager.createStoredProcedureQuery( "sp_count_phones" );
query.registerStoredProcedureParameter( "personId", Long.class, ParameterMode.IN );
query.registerStoredProcedureParameter( "phoneCount", Long.class, ParameterMode.OUT );
query.setParameter( "personId", 1L );
query.execute();
Long phoneCount = (Long) query.getOutputParameterValue( "phoneCount" );
Example 613. Calling a MySQL stored procedure with OUT
parameter type using Hibernate
Session session = entityManager.unwrap( Session.class );
ProcedureCall call = session.createStoredProcedureCall( "sp_count_phones" );
ProcedureParameter<Long> parameter = call.registerParameter( "personId", Long.class, ParameterMode.IN );
call.setParameter( parameter, 1L );
call.registerParameter( "phoneCount", Long.class, ParameterMode.OUT );
Long phoneCount = (Long) call.getOutputs().getOutputParameterValue( "phoneCount" );
assertEquals( Long.valueOf( 2 ), phoneCount );
If the stored procedure outputs the result directly without an OUT
parameter type:
Example 614. MySQL stored procedure without an OUT
parameter type
statement.executeUpdate(
"CREATE PROCEDURE sp_phones(IN personId INT) " +
"BEGIN " +
" SELECT * " +
" FROM Phone " +
" WHERE person_id = personId; " +
"END"
);
You can retrieve the results of the aforementioned MySQL stored procedure as follows:
Example 615. Calling a MySQL stored procedure and fetching the result set without an OUT
parameter type using Jakarta Persistence
StoredProcedureQuery query = entityManager.createStoredProcedureQuery( "sp_phones" );
query.registerStoredProcedureParameter( 1, Long.class, ParameterMode.IN );
query.setParameter( 1, 1L );
List<Object[]> personComments = query.getResultList();
Example 616. Calling a MySQL stored procedure and fetching the result set without an OUT
parameter type using Hibernate
Session session = entityManager.unwrap( Session.class );
ProcedureCall call = session.createStoredProcedureCall( "sp_phones" );
ProcedureParameter<Long> parameter = call.registerParameter( 1, Long.class, ParameterMode.IN );
call.setParameter( parameter, 1L );
Output output = call.getOutputs().getCurrent();
List<Object[]> personComments = ( (ResultSetOutput) output ).getResultList();
For a REF_CURSOR
result sets, we’ll consider the following Oracle stored procedure:
Example 617. Oracle REF_CURSOR
stored procedure
statement.executeUpdate(
"CREATE OR REPLACE PROCEDURE sp_person_phones (" +
" personId IN NUMBER, " +
" personPhones OUT SYS_REFCURSOR) " +
"AS " +
"BEGIN " +
" OPEN personPhones FOR " +
" SELECT *" +
" FROM phone " +
" WHERE person_id = personId; " +
"END;"
);
|
This function can be called using the standard Java Persistence API:
Example 618. Calling an Oracle REF_CURSOR
stored procedure using Jakarta Persistence
StoredProcedureQuery query = entityManager.createStoredProcedureQuery("sp_person_phones");
query.registerStoredProcedureParameter(1, Long.class, ParameterMode.IN);
query.registerStoredProcedureParameter(2, Class.class, ParameterMode.REF_CURSOR);
query.setParameter(1, 1L);
query.execute();
List<Object[]> postComments = query.getResultList();
Example 619. Calling an Oracle REF_CURSOR
stored procedure using Hibernate
Session session = entityManager.unwrap(Session.class);
ProcedureCall call = session.createStoredProcedureCall("sp_person_phones");
ProcedureParameter<Long> parameter = call.registerParameter(1, Long.class, ParameterMode.IN);
call.setParameter(parameter, 1L);
call.registerParameter(2, Class.class, ParameterMode.REF_CURSOR);
Output output = call.getOutputs().getCurrent();
List<Object[]> postComments = ((ResultSetOutput) output).getResultList();
assertEquals(2, postComments.size());
If the database defines an SQL function:
Example 620. MySQL function
statement.executeUpdate(
"CREATE FUNCTION fn_count_phones(personId integer) " +
"RETURNS integer " +
"DETERMINISTIC " +
"READS SQL DATA " +
"BEGIN " +
" DECLARE phoneCount integer; " +
" SELECT COUNT(*) INTO phoneCount " +
" FROM Phone p " +
" WHERE p.person_id = personId; " +
" RETURN phoneCount; " +
"END"
);
Because the current StoredProcedureQuery
implementation doesn’t yet support SQL functions,
we need to use the JDBC syntax.
This limitation is acknowledged and will be addressed by the HHH-10530 issue. |
Example 621. Calling a MySQL function
final AtomicReference<Integer> phoneCount = new AtomicReference<>();
Session session = entityManager.unwrap( Session.class );
session.doWork( connection -> {
try (CallableStatement function = connection.prepareCall(
"{ ? = call fn_count_phones(?) }" )) {
function.registerOutParameter( 1, Types.INTEGER );
function.setInt( 2, 1 );
function.execute();
phoneCount.set( function.getInt( 1 ) );
}
} );
Stored procedure queries cannot be paged with Since these servers can return multiple result sets and update counts, For SQL Server, if you can enable |
18.13. Using named queries to call stored procedures
Just like with SQL statements, you can also use named queries to call stored procedures.
For this purpose, Jakarta Persistence defines the @NamedStoredProcedureQuery
annotation.
Example 622. Oracle REF_CURSOR
named query stored procedure
@NamedStoredProcedureQuery(
name = "sp_person_phones",
procedureName = "sp_person_phones",
parameters = {
@StoredProcedureParameter(
name = "personId",
type = Long.class,
mode = ParameterMode.IN
),
@StoredProcedureParameter(
name = "personPhones",
type = Class.class,
mode = ParameterMode.REF_CURSOR
)
}
)
Calling this stored procedure is straightforward, as illustrated by the following example.
Example 623. Calling an Oracle REF_CURSOR
stored procedure using a Jakarta Persistence named query
List<Object[]> postComments = entityManager
.createNamedStoredProcedureQuery("sp_person_phones")
.setParameter("personId", 1L)
.getResultList();
18.14. Custom SQL for CRUD (Create, Read, Update and Delete)
Hibernate can use custom SQL for CRUD operations.
The SQL can be overridden at the statement level or individual column level.
This section describes statement overrides.
For columns, see Column transformers: read and write expressions.
The following example shows how to define custom SQL operations using annotations.
@SQLInsert
, @SQLUpdate
, and @SQLDelete
override the INSERT, UPDATE, DELETE statements of a given entity.
Similarly, @SQLSelect
specifies a custom SELECT query used for loading the underlying table record.
For collections, Hibernate allows defining a custom @SQLDeleteAll
which is used for removing all child records associated with a given parent entity.
To filter collections, the @SQLRestriction
annotation allows customizing the underlying SQL WHERE clause.
Example 624. Custom CRUD
@Entity(name = "Person")
@SQLInsert(
sql = "INSERT INTO person (name, id, valid) VALUES (?, ?, true) ",
check = ResultCheckStyle.COUNT
)
@SQLUpdate(
sql = "UPDATE person SET name = ? where id = ? "
)
@SQLDelete(
sql = "UPDATE person SET valid = false WHERE id = ? "
)
@SQLSelect(
sql ="SELECT id, name FROM person WHERE id = ? and valid = true"
)
public static class Person {
@Id
@GeneratedValue
private Long id;
private String name;
@ElementCollection
@SQLInsert(
sql = "INSERT INTO person_phones (person_id, phones, valid) VALUES (?, ?, true) ")
@SQLDeleteAll(
sql = "UPDATE person_phones SET valid = false WHERE person_id = ?")
@SQLRestriction("valid = true")
private List<String> phones = new ArrayList<>();
//Getters and setters are omitted for brevity
}
In the example above, the entity is mapped so that entries are soft-deleted (the records are not removed from the database, but instead, a flag marks the row validity).
The Person
entity benefits from custom INSERT, UPDATE, and DELETE statements which update the valid
column accordingly.
The custom @SQLSelect
is used to retrieve only Person
rows that are valid.
The same is done for the phones
collection. The @SQLDeleteAll
and the SQLInsert
queries are used whenever the collection is modified.
You can also call a store procedure using the custom CRUD statements. |
To check that the execution happens correctly, Hibernate allows you to define one of those three strategies:
-
none: no check is performed; the store procedure is expected to fail upon constraint violations.
-
count: use of row-count returned by the
executeUpdate()
method call to check that the update was successful. -
param: like count but using a
CallableStatement
output parameter.
To define the result check style, use the check
parameter.
The parameter order is important and is defined by the order Hibernate handles properties. To see the expected sequence, remember to not include your custom SQL through annotations or mapping files as that will override the Hibernate generated static SQL. |
Overriding SQL statements for secondary tables is also possible.
Example 625. Overriding SQL statements for secondary tables
@Entity(name = "Person")
@Table(name = "person")
@SecondaryTable(name = "person_details",
pkJoinColumns = @PrimaryKeyJoinColumn(name = "person_id"))
@SQLInsert(
sql = "INSERT INTO person (name, id, valid) VALUES (?, ?, true) "
)
@SQLDelete(
sql = "UPDATE person SET valid = false WHERE id = ? "
)
@SQLInsert(
table = "person_details",
sql = "INSERT INTO person_details (image, person_id, valid) VALUES (?, ?, true) ",
check = ResultCheckStyle.COUNT
)
@SQLDelete(
table = "person_details",
sql = "UPDATE person_details SET valid = false WHERE person_id = ? "
)
@Loader(namedQuery = "find_valid_person")
@NamedNativeQueries({
@NamedNativeQuery(
name = "find_valid_person",
query = "SELECT " +
" p.id, " +
" p.name, " +
" pd.image " +
"FROM person p " +
"LEFT OUTER JOIN person_details pd ON p.id = pd.person_id " +
"WHERE p.id = ? AND p.valid = true AND pd.valid = true",
resultClass = Person.class
)
})
public static class Person {
@Id
@GeneratedValue
private Long id;
private String name;
@Column(name = "image", table = "person_details")
private byte[] image;
//Getters and setters are omitted for brevity
}
The SQL is directly executed in your database, so you can use any dialect you like. |
You can also use stored procedures for customizing the CRUD statements.
Assuming the following stored procedure:
Example 626. Oracle stored procedure to soft-delete a given entity
statement.executeUpdate(
"CREATE OR REPLACE PROCEDURE sp_delete_person (" +
" personId IN NUMBER) " +
"AS " +
"BEGIN " +
" UPDATE person SET valid = 0 WHERE id = personId; " +
"END;"
);
}
The entity can use this stored procedure to soft-delete the entity in question:
Example 627. Customizing the entity delete statement to use the Oracle stored procedure= instead
@SQLDelete(
sql = "{ call sp_delete_person(?) } ",
callable = true
)
You need to set the |
19. Spatial
19.1. Overview
Hibernate Spatial was originally developed as a generic extension to Hibernate for handling geographic data.
Since 5.0, Hibernate Spatial is now part of the Hibernate ORM project,
and it allows you to deal with geographic data in a standardized way.
Hibernate Spatial provides a standardized, cross-database interface to geographic data storage and query functions.
It supports most of the functions described by the OGC Simple Feature Specification. Supported databases are Oracle 10g/11g,
PostgreSQL/PostGIS, MySQL, Microsoft SQL Server, DB2, CockroachDB and H2/GeoDB.
Spatial data types are not part of the Java standard library, and they are absent from the JDBC specification.
Over the years JTS has emerged as the de facto standard to fill this gap. JTS is
an implementation of the Simple Feature Specification (SFS). Many databases
on the other hand implement the SQL/MM — Part 3: Spatial Data specification — a related, but broader specification. The biggest difference is that
SFS is limited to 2D geometries in the projected plane (although JTS supports 3D coordinates), whereas
SQL/MM supports 2-, 3- or 4-dimensional coordinate spaces.
Hibernate Spatial supports two different geometry models: JTS and
geolatte-geom. As already mentioned, JTS is the de facto
standard. Geolatte-geom (also written by the lead developer of Hibernate Spatial) is a more recent library that
supports many features specified in SQL/MM but not available in JTS (such as support for 4D geometries, and support for extended WKT/WKB formats).
Geolatte-geom also implements encoders/decoders for the database native types. Geolatte-geom has good interoperability with
JTS. Converting a Geolatte geometry
to a JTS geometry
, for instance, doesn’t require copying of the coordinates.
It also delegates spatial processing to JTS.
Whether you use JTS or Geolatte-geom, Hibernate spatial maps the database spatial types to your geometry model of choice. It will, however,
always use Geolatte-geom to decode the database native types.
Hibernate Spatial also makes a number of spatial functions available in HQL and in the Criteria Query API. These functions are
specified in both SQL/MM as SFS, and are commonly implemented in databases with spatial support (see Hibernate Spatial dialect function support)
19.2. Configuration
Hibernate Spatial requires some configuration prior to start using it.
19.2.1. Dependency
You need to include the hibernate-spatial
dependency in your build environment.
For Maven, you need to add the following dependency:
Example 628. Maven dependency
<dependency>
<groupId>org.hibernate.orm</groupId>
<artifactId>hibernate-spatial</artifactId>
<version>${hibernate.version}</version>
</dependency>
Hibernate defines common spatial functions uniformly over all databases. These
functions largely correspond to those specified in the Simple Feature Specification. Not all databases are capable of supporting every function, however. The table below details which functions are supported by various database systems.
Function |
Description |
PostgresSQL |
Oracle 10g/11g |
MySQL |
SQLServer |
H2GIS |
DB2 |
CockroachDB |
Basic functions on Geometry |
||||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
|
SFS §2.1.1.1 |
|||||||
Functions for testing Spatial Relations between geometric objects |
||||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
|
SFS §2.1.1.2 |
|||||||
Functions that support Spatial Analysis |
||||||||
|
SFS §2.1.1.3 |
|||||||
|
SFS §2.1.1.3 |
|||||||
|
SFS §2.1.1.3 |
(1) |
||||||
|
SFS §2.1.1.3 |
(1) |
||||||
|
SFS §2.1.1.3 (renamed from union) |
(1) |
||||||
|
SFS §2.1.1.3 |
(1) |
||||||
|
SFS §2.1.1.3 |
(1) |
||||||
Common non-SFS functions |
||||||||
|
Returns true if the geometries are within the specified distance of one another |
|||||||
|
Returns a new geometry with its coordinates transformed to the SRID referenced by the integer parameter |
|||||||
Spatial st_aggregate Functions |
||||||||
|
Returns a bounding box that bounds the set of returned geometries |
(1) Argument Geometries need to have the same dimensionality.
Note that beyond the common spatial functions mentioned above, Hibernate may define additional spatial functions for each database dialect. These will be documented in the
Database notes below.
19.3. Database notes
- Postgresql
-
The Postgresql dialect has support for the Postgis spatial extension, but not the Geometric types mentioned in the
Postgresql documentation.
In addition to the common spatial functions, the following functions are supported:
Function |
Purpose |
Syntax |
Postgis function operator |
|
2D distance between two geometries |
|
<-> |
|
2D distance between the bounding boxes of tow geometries |
|
<#> |
|
3D distance between 2 trajectories |
|
|=| |
|
the n-D distance between the centroids of the bounding boxes of two geometries |
|
<<->> |
- MySQL
-
MySQL versions before 5.6.1 had only limited support for spatial operators.
Most operators only took account of the minimum bounding rectangles (MBR) of the geometries, and not the geometries themselves.This changed in version 5.6.1, when MySQL introduced
ST_*
spatial operators.
The dialectMySQLSpatial56Dialect
uses these newer, more precise operators.
- Oracle10g/11g
-
There is currently only support for the
SDO_GEOMETRY
type.The
SDOGeometryType
requires access to anOracleConnection
object when converting a geometry to SDO_GEOMETRY.
In some environments, however, theOracleConnection
is not available (e.g. because a Java EE container or connection pool proxy wraps the connection object in its ownConnection
implementation).
AConnectionFinder
knows how to retrieve theOracleConnection
from the wrapper or proxy Connection object that is passed into prepared statements. It can be configured with thehibernate.spatial.connection_finder
property:When the passed object is not already an
OracleConnection
, the default implementation will attempt to retrieve theOracleConnection
by recursive reflection.
It will search for methods that returnConnection
objects, execute these methods and check the result.
If the result is of typeOracleConnection
the object is returned.
Otherwise, it recurses on it.In may cases, this strategy will suffice.
If not, you can provide your own implementation of this interface on the classpath, and configure it in thehibernate.spatial.connection_finder
property.
Note that implementations must be thread-safe and have a default no-args constructor. - SQL Server
-
The
GEOGRAPHY
type is not currently supported. - CockroachDB
-
The dialect
CockroachDialect
supports theGEOMETRY
type in CockroachDB v20.2 and later. TheGEOGRAPHY
type is currently not supported. - H2GIS
-
The
H2Dialect
supports H2GIS, a spatial extension of the H2 in-memory database. This dialect can be used as a replacement for theGeoDB
dialect that was supported in previous versions. The major difference withGeoDB
is that theGEOGRAPHY
column type is currently not present inH2GIS
. - DB2
-
The
DB2SpatialDialect
supports the spatial extensions of the DB2 LUW database.
The dialect has been tested with DB2 LUW 11.1.
The dialect does not support DB2 for z/OS or DB2 column-oriented databases.In order to use the DB2 Hibernate Spatial capabilities, it is necessary to first execute the following
SQL statements which will allow DB2 to accept Extended WellKnown Text (EWKT) data and return EWKT data.
One way to do this is to copy these statements into a file such as ewkt.sql and execute it in a DB2 command window
with a command such asdb2 -tvf ewkt.sql
.
create or replace function db2gse.asewkt(geometry db2gse.st_geometry)
returns clob(2G)
specific db2gse.asewkt1
language sql
deterministic
no external action
reads sql data
return 'srid=' || varchar(db2gse.st_srsid(geometry)) || ';' || db2gse.st_astext(geometry);
create or replace function db2gse.geomfromewkt(instring varchar(32000))
returns db2gse.st_geometry
specific db2gse.fromewkt1
language sql
deterministic
no external action
reads sql data
return db2gse.st_geometry(
substr(instring,posstr(instring,';')+1, length(instring) - posstr(instring,';')),
integer(substr(instring,posstr(instring,'=')+1,posstr(instring,';')-(posstr(instring,'=')+1))));
create transform for db2gse.st_geometry ewkt (
from sql with function db2gse.asewkt(db2gse.st_geometry),
to sql with function db2gse.geomfromewkt(varchar(32000)) );
drop transform db2_program for db2gse.st_geometry;
create transform for db2gse.st_geometry db2_program (
from sql with function db2gse.asewkt(db2gse.st_geometry),
to sql with function db2gse.geomfromewkt(varchar(32000)) );
19.4. Types
It suffices to declare a property as either a JTS or a Geolatte-geom Geometry
and Hibernate Spatial will map it using the
relevant type.
Here is an example using JTS:
Example 629. Type mapping
import org.locationtech.jts.geom.Point;
@Entity(name = "Event")
public static class Event {
@Id
private Long id;
private String name;
private Point location;
//Getters and setters are omitted for brevity
}
We can now treat spatial geometries like any other type.
Example 630. Creating a Point
Event event = new Event();
event.setId( 1L);
event.setName( "Hibernate ORM presentation");
Point point = geometryFactory.createPoint( new Coordinate( 10, 5 ) );
event.setLocation( point );
entityManager.persist( event );
Spatial Dialects defines many query functions that are available both in HQL and JPQL queries. Below we show how we
could use the within
function to find all objects within a given spatial extent or window.
Example 631. Querying the geometry
Polygon window = geometryFactory.createPolygon( coordinates );
Event event = entityManager.createQuery(
"select e " +
"from Event e " +
"where within(e.location, :window) = true", Event.class)
.setParameter("window", window)
.getSingleResult();
20. Multitenancy
20.1. What is multitenancy?
The term multitenancy, in general, is applied to software development to indicate an architecture in which a single running instance of an application simultaneously serves multiple clients (tenants).
This is highly common in SaaS solutions.
Isolating information (data, customizations, etc.) pertaining to the various tenants is a particular challenge in these systems.
This includes the data owned by each tenant stored in the database.
It is this last piece, sometimes called multitenant data, that we will focus on.
20.2. Multitenant data approaches
There are three main approaches to isolating information in these multitenant systems which go hand-in-hand with different database schema definitions and JDBC setups.
Each multitenancy strategy has pros and cons as well as specific techniques and considerations. |
20.2.1. Separate database
Each tenant’s data is kept in a physically separate database instance.
JDBC Connections would point specifically to each database so any pooling would be per-tenant.
A general application approach, here, would be to define a JDBC Connection pool per-tenant and to select the pool to use based on the tenant identifier associated with the currently logged in user.
20.2.2. Separate schema
Each tenant’s data is kept in a distinct database schema on a single database instance.
There are two different ways to define JDBC Connections here:
-
Connections could point specifically to each schema as we saw with the
Separate database
approach.
This is an option provided that the driver supports naming the default schema in the connection URL or if the pooling mechanism supports naming a schema to use for its Connections.
Using this approach, we would have a distinct JDBC Connection pool per-tenant where the pool to use would be selected based on the «tenant identifier» associated with the currently logged in user. -
Connections could point to the database itself (using some default schema) but the Connections would be altered using the SQL
SET SCHEMA
(or similar) command.
Using this approach, we would have a single JDBC Connection pool for use to service all tenants, but before using the Connection, it would be altered to reference the schema named by the «tenant identifier» associated with the currently logged in user.
20.2.3. Partitioned (discriminator) data
All data is kept in a single database schema.
The data for each tenant is partitioned by the use of partition value or discriminator.
The complexity of this discriminator might range from a simple column value to a complex SQL formula.
Again, this approach would use a single Connection pool to service all tenants.
However, in this approach, the application needs to alter each and every SQL statement sent to the database to reference the «tenant identifier» discriminator.
20.3. Multitenancy in Hibernate
Using Hibernate with multitenant data comes down to both an API and then integration piece(s).
As usual, Hibernate strives to keep the API simple and isolated from any underlying integration complexities.
The API is really just defined by passing the tenant identifier as part of opening any session.
Example 632. Specifying tenant identifier from SessionFactory
private void doInSession(String tenant, Consumer<Session> function) {
Session session = null;
Transaction txn = null;
try {
session = sessionFactory
.withOptions()
.tenantIdentifier(tenant)
.openSession();
txn = session.getTransaction();
txn.begin();
function.accept(session);
txn.commit();
} catch (Throwable e) {
if (txn != null) txn.rollback();
throw e;
} finally {
if (session != null) {
session.close();
}
}
}
20.3.1. @TenantId
For the partitioned data approach, each entity representing partitioned data must declare a field
annotated @TenantId
.
Example 633. A @TenantId
usage example
@Entity
public class Account {
@Id @GeneratedValue Long id;
@TenantId String tenantId;
...
}
The @TenantId
field is automatically populated by Hibernate when an instance is made
persistent.
20.3.2. MultiTenantConnectionProvider
When using either the separate database or separate schema approach, Hibernate needs to be able to obtain connections in a tenant-specific manner.
That is the role of the MultiTenantConnectionProvider
contract.
Application developers will need to provide an implementation of this contract.
Most of its methods are extremely self-explanatory.
The only ones which might not be are getAnyConnection
and releaseAnyConnection
.
It is important to note also that these methods do not accept the tenant identifier.
Hibernate uses these methods during startup to perform various configuration, mainly via the java.sql.DatabaseMetaData
object.
The MultiTenantConnectionProvider
to use can be specified in a number of ways:
-
Use the
hibernate.multi_tenant_connection_provider
setting.
It could name aMultiTenantConnectionProvider
instance, aMultiTenantConnectionProvider
implementation class reference or aMultiTenantConnectionProvider
implementation class name. -
Passed directly to the
org.hibernate.boot.registry.StandardServiceRegistryBuilder
. -
If none of the above options match, but the settings do specify a
hibernate.connection.datasource
value,
Hibernate will assume it should use the specificDataSourceBasedMultiTenantConnectionProviderImpl
implementation which works on a number of pretty reasonable assumptions when running inside of an app server and using onejavax.sql.DataSource
per tenant.
See its Javadocs for more details.
The following example portrays a MultiTenantConnectionProvider
implementation that handles multiple ConnectionProvider
s.
Example 634. A MultiTenantConnectionProvider
implementation
public class ConfigurableMultiTenantConnectionProvider
extends AbstractMultiTenantConnectionProvider {
private final Map<String, ConnectionProvider> connectionProviderMap =
new HashMap<>();
public ConfigurableMultiTenantConnectionProvider(
Map<String, ConnectionProvider> connectionProviderMap) {
this.connectionProviderMap.putAll(connectionProviderMap);
}
@Override
protected ConnectionProvider getAnyConnectionProvider() {
return connectionProviderMap.values().iterator().next();
}
@Override
protected ConnectionProvider selectConnectionProvider(String tenantIdentifier) {
return connectionProviderMap.get(tenantIdentifier);
}
}
The ConfigurableMultiTenantConnectionProvider
can be set up as follows:
Example 635. A MultiTenantConnectionProvider
usage example
private void init() {
registerConnectionProvider(FRONT_END_TENANT);
registerConnectionProvider(BACK_END_TENANT);
Map<String, Object> settings = new HashMap<>();
settings.put(AvailableSettings.MULTI_TENANT_CONNECTION_PROVIDER,
new ConfigurableMultiTenantConnectionProvider(connectionProviderMap));
sessionFactory = sessionFactory(settings);
}
protected void registerConnectionProvider(String tenantIdentifier) {
Properties properties = properties();
properties.put(Environment.URL,
tenantUrl(properties.getProperty(Environment.URL), tenantIdentifier));
DriverManagerConnectionProviderImpl connectionProvider =
new DriverManagerConnectionProviderImpl();
connectionProvider.configure( PropertiesHelper.map(properties) );
connectionProviderMap.put(tenantIdentifier, connectionProvider);
}
When using multitenancy, it’s possible to save an entity with the same identifier across different tenants:
Example 636. An example of saving entities with the same identifier across different tenants
doInSession(FRONT_END_TENANT, session -> {
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
session.persist(person);
});
doInSession(BACK_END_TENANT, session -> {
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
session.persist(person);
});
20.3.3. CurrentTenantIdentifierResolver
org.hibernate.context.spi.CurrentTenantIdentifierResolver
is a contract for Hibernate to be able to resolve what the application considers the current tenant identifier.
The implementation to use can be either passed directly to Configuration
via its setCurrentTenantIdentifierResolver
method,
or be specified via the hibernate.tenant_identifier_resolver
setting.
There are two situations where CurrentTenantIdentifierResolver
is used:
-
The first situation is when the application is using the
org.hibernate.context.spi.CurrentSessionContext
feature in conjunction with multitenancy.
In the case of the current-session feature, Hibernate will need to open a session if it cannot find an existing one in scope.
However, when a session is opened in a multitenant environment, the tenant identifier has to be specified.
This is where theCurrentTenantIdentifierResolver
comes into play; Hibernate will consult the implementation you provide to determine the tenant identifier to use when opening the session.
In this case, it is required that aCurrentTenantIdentifierResolver
is supplied. -
The other situation is when you do not want to explicitly specify the tenant identifier all the time.
If aCurrentTenantIdentifierResolver
has been specified, Hibernate will use it to determine the default tenant identifier to use when opening the session.
Additionally, if the CurrentTenantIdentifierResolver
implementation returns true
for its validateExistingCurrentSessions
method, Hibernate will make sure any existing sessions that are found in scope have a matching tenant identifier.
This capability is only pertinent when the CurrentTenantIdentifierResolver
is used in current-session settings.
20.3.4. Caching
Multitenancy support in Hibernate works seamlessly with the Hibernate second level cache.
The key used to cache data encodes the tenant identifier.
Currently, schema export will not really work with multitenancy. |
20.3.5. Multitenancy Hibernate Session configuration
When using multitenancy, you might want to configure each tenant-specific Session
differently.
For instance, each tenant could specify a different time zone configuration.
Example 637. Registering the tenant-specific time zone information
registerConnectionProvider(FRONT_END_TENANT, TimeZone.getTimeZone("UTC"));
registerConnectionProvider(BACK_END_TENANT, TimeZone.getTimeZone("CST"));
The registerConnectionProvider
method is used to define the tenant-specific context.
Example 638. The registerConnectionProvider
method used for defining the tenant-specific context
protected void registerConnectionProvider(String tenantIdentifier, TimeZone timeZone) {
Properties properties = properties();
properties.put(
Environment.URL,
tenantUrl( properties.getProperty(Environment.URL), tenantIdentifier )
);
DriverManagerConnectionProviderImpl connectionProvider =
new DriverManagerConnectionProviderImpl();
connectionProvider.configure( PropertiesHelper.map(properties) );
connectionProviderMap.put(tenantIdentifier, connectionProvider);
timeZoneTenantMap.put(tenantIdentifier, timeZone);
}
For our example, the tenant-specific context is held in the connectionProviderMap
and timeZoneTenantMap
.
private Map<String, ConnectionProvider> connectionProviderMap = new HashMap<>();
private Map<String, TimeZone> timeZoneTenantMap = new HashMap<>();
Now, when building the Hibernate Session
, aside from passing the tenant identifier,
we could also configure the Session
to use the tenant-specific time zone.
Example 639. The Hibernate Session
can be configured using the tenant-specific context
private void doInSession(String tenant, Consumer<Session> function, boolean useTenantTimeZone) {
Session session = null;
Transaction txn = null;
try {
SessionBuilder sessionBuilder = sessionFactory
.withOptions()
.tenantIdentifier(tenant);
if (useTenantTimeZone) {
sessionBuilder.jdbcTimeZone(timeZoneTenantMap.get(tenant));
}
session = sessionBuilder.openSession();
txn = session.getTransaction();
txn.begin();
function.accept(session);
txn.commit();
}
catch (Throwable e) {
if (txn != null) {
txn.rollback();
}
throw e;
}
finally {
if (session != null) {
session.close();
}
}
}
So, if we set the useTenantTimeZone
parameter to true
, Hibernate will persist the Timestamp
properties using the
tenant-specific time zone. As you can see in the following example, the Timestamp
is successfully retrieved
even if the currently running JVM uses a different time zone.
Example 640. The useTenantTimeZone
allows you to persist a Timestamp
in the provided time zone
doInSession(FRONT_END_TENANT, session -> {
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
person.setCreatedOn(LocalDateTime.of(2018, 11, 23, 12, 0, 0));
session.persist(person);
}, true);
doInSession(BACK_END_TENANT, session -> {
Person person = new Person();
person.setId(1L);
person.setName("John Doe");
person.setCreatedOn(LocalDateTime.of(2018, 11, 23, 12, 0, 0));
session.persist(person);
}, true);
doInSession(FRONT_END_TENANT, session -> {
Timestamp personCreationTimestamp = (Timestamp) session
.createNativeQuery(
"select p.created_on " +
"from Person p " +
"where p.id = :personId", Timestamp.class)
.setParameter("personId", 1L)
.getSingleResult();
assertEquals(
Timestamp.valueOf(LocalDateTime.of(2018, 11, 23, 12, 0, 0)),
personCreationTimestamp
);
}, true);
doInSession(BACK_END_TENANT, session -> {
Timestamp personCreationTimestamp = (Timestamp) session
.createNativeQuery(
"select p.created_on " +
"from Person p " +
"where p.id = :personId", Timestamp.class)
.setParameter("personId", 1L)
.getSingleResult();
assertEquals(
Timestamp.valueOf(LocalDateTime.of(2018, 11, 23, 12, 0, 0)),
personCreationTimestamp
);
}, true);
However, behind the scenes, we can see that Hibernate has saved the created_on
property in the tenant-specific time zone.
The following example shows you that the Timestamp
was saved in the UTC time zone, hence the offset displayed in the
test output.
Example 641. With the useTenantTimeZone
property set to false
, the Timestamp
is fetched in the tenant-specific time zone
doInSession(FRONT_END_TENANT, session -> {
Timestamp personCreationTimestamp = (Timestamp) session
.createNativeQuery(
"select p.created_on " +
"from Person p " +
"where p.id = :personId", Timestamp.class)
.setParameter("personId", 1L)
.getSingleResult();
log.infof(
"The created_on timestamp value is: [%s]",
personCreationTimestamp
);
long timeZoneOffsetMillis =
Timestamp.valueOf(LocalDateTime.of(2018, 11, 23, 12, 0, 0)).getTime() -
personCreationTimestamp.getTime();
assertEquals(
TimeZone.getTimeZone(ZoneId.systemDefault()).getRawOffset(),
timeZoneOffsetMillis
);
log.infof(
"For the current time zone: [%s], the UTC time zone offset is: [%d]",
TimeZone.getDefault().getDisplayName(), timeZoneOffsetMillis
);
}, false);
SELECT
p.created_on
FROM
Person p
WHERE
p.id = ?
-- binding parameter [1] as [BIGINT] - [1]
-- extracted value ([CREATED_ON] : [TIMESTAMP]) - [2018-11-23 10:00:00.0]
-- The created_on timestamp value is: [2018-11-23 10:00:00.0]
-- For the current time zone: [Eastern European Time], the UTC time zone offset is: [7200000]
Notice that for the Eastern European Time
time zone, the time zone offset was 2 hours when the test was executed.
21. Envers
21.1. Basics
To audit changes that are performed on an entity, you only need two things:
-
the
hibernate-envers
jar on the classpath, -
an
@Audited
annotation on the entity.
Unlike in previous versions, you no longer need to specify listeners in the Hibernate configuration file. |
And that’s all.
You can create, modify and delete the entities as always.
The use of Jakarta Persistence’s |
If you look at the generated schema for your entities, or at the data persisted by Hibernate, you will notice that there are no changes.
However, for each audited entity, a new table is introduced — entity_table_AUD
, which stores the historical data, whenever you commit a transaction.
Envers automatically creates audit tables if |
Considering we have a Customer
entity, when annotating it with the Audited
annotation,
Hibernate is going to generate the following tables using the hibernate.hbm2ddl.auto
schema tool:
Example 642. Basic Envers entity mapping
@Audited
@Entity(name = "Customer")
public static class Customer {
@Id
private Long id;
private String firstName;
private String lastName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_on")
@CreationTimestamp
private Date createdOn;
//Getters and setters are omitted for brevity
}
create table Customer (
id bigint not null,
created_on timestamp,
firstName varchar(255),
lastName varchar(255),
primary key (id)
)
create table Customer_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint,
created_on timestamp,
firstName varchar(255),
lastName varchar(255),
primary key (id, REV)
)
create table REVINFO (
REV integer generated by default as identity,
REVTSTMP bigint,
primary key (REV)
)
alter table Customer_AUD
add constraint FK5ecvi1a0ykunrriib7j28vpdj
foreign key (REV)
references REVINFO
Instead of annotating the whole class and auditing all properties, you can annotate only some persistent properties with @Audited
.
This will cause only these properties to be audited.
Now, considering the previous Customer
entity,
let’s see how Envers auditing works when inserting, updating, and deleting the entity in question.
Example 643. Auditing the entity INSERT
operation
Customer customer = new Customer();
customer.setId(1L);
customer.setFirstName("John");
customer.setLastName("Doe");
entityManager.persist(customer);
insert
into
Customer
(created_on, firstName, lastName, id)
values
(?, ?, ?, ?)
-- binding parameter [1] as [TIMESTAMP] - [Mon Jul 24 17:21:32 EEST 2017]
-- binding parameter [2] as [VARCHAR] - [John]
-- binding parameter [3] as [VARCHAR] - [Doe]
-- binding parameter [4] as [BIGINT] - [1]
insert
into
REVINFO
(REV, REVTSTMP)
values
(?, ?)
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [BIGINT] - [1500906092803]
insert
into
Customer_AUD
(REVTYPE, created_on, firstName, lastName, id, REV)
values
(?, ?, ?, ?, ?, ?)
-- binding parameter [1] as [INTEGER] - [0]
-- binding parameter [2] as [TIMESTAMP] - [Mon Jul 24 17:21:32 EEST 2017]
-- binding parameter [3] as [VARCHAR] - [John]
-- binding parameter [4] as [VARCHAR] - [Doe]
-- binding parameter [5] as [BIGINT] - [1]
-- binding parameter [6] as [INTEGER] - [1]
Example 644. Auditing the entity UPDATE
operation
Customer customer = entityManager.find(Customer.class, 1L);
customer.setLastName("Doe Jr.");
update
Customer
set
created_on=?,
firstName=?,
lastName=?
where
id=?
-- binding parameter [1] as [TIMESTAMP] - [2017-07-24 17:21:32.757]
-- binding parameter [2] as [VARCHAR] - [John]
-- binding parameter [3] as [VARCHAR] - [Doe Jr.]
-- binding parameter [4] as [BIGINT] - [1]
insert
into
REVINFO
(REV, REVTSTMP)
values
(?, ?)
-- binding parameter [1] as [BIGINT] - [2]
-- binding parameter [2] as [BIGINT] - [1500906092853]
insert
into
Customer_AUD
(REVTYPE, created_on, firstName, lastName, id, REV)
values
(?, ?, ?, ?, ?, ?)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [TIMESTAMP] - [2017-07-24 17:21:32.757]
-- binding parameter [3] as [VARCHAR] - [John]
-- binding parameter [4] as [VARCHAR] - [Doe Jr.]
-- binding parameter [5] as [BIGINT] - [1]
-- binding parameter [6] as [INTEGER] - [2]
Example 645. Auditing the entity DELETE
operation
Customer customer = entityManager.getReference(Customer.class, 1L);
entityManager.remove(customer);
delete
from
Customer
where
id = ?
-- binding parameter [1] as [BIGINT] - [1]
insert
into
REVINFO
(REV, REVTSTMP)
values
(?, ?)
-- binding parameter [1] as [BIGINT] - [3]
-- binding parameter [2] as [BIGINT] - [1500906092876]
insert
into
Customer_AUD
(REVTYPE, created_on, firstName, lastName, id, REV)
values
(?, ?, ?, ?, ?, ?)
-- binding parameter [1] as [INTEGER] - [2]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [VARCHAR] - [null]
-- binding parameter [4] as [VARCHAR] - [null]
-- binding parameter [5] as [BIGINT] - [1]
-- binding parameter [6] as [INTEGER] - [3]
The REVTYPE
column value is taken from the RevisionType
Enum.
Database column value |
Associated |
Description |
0 |
|
A database table row was inserted. |
1 |
|
A database table row was updated. |
2 |
|
A database table row was deleted. |
The audit (history) of an entity can be accessed using the AuditReader
interface, which can be obtained by having an open EntityManager
or Session
via the AuditReaderFactory
.
Example 646. Getting a list of revisions for the Customer
entity
List<Number> revisions = scope.fromTransaction( entityManager -> {
return AuditReaderFactory.get(entityManager).getRevisions(
Customer.class,
1L
);
});
select
c.REV as col_0_0_
from
Customer_AUD c
cross join
REVINFO r
where
c.id = ?
and c.REV = r.REV
order by
c.REV asc
-- binding parameter [1] as [BIGINT] - [1]
Using the previously fetched revisions, we can now inspect the state of the Customer
entity at that particular revision:
Example 647. Getting the first revision for the Customer
entity
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(0))
.getSingleResult();
assertEquals("Doe", customer.getLastName());
select
c.id as id1_1_,
c.REV as REV2_1_,
c.REVTYPE as REVTYPE3_1_,
c.created_on as created_4_1_,
c.firstName as firstNam5_1_,
c.lastName as lastName6_1_
from
Customer_AUD c
where
c.REV = (
select
max( c_max.REV )
from
Customer_AUD c_max
where
c_max.REV <= ?
and c.id = c_max.id
)
and c.REVTYPE <> ?
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
When executing the aforementioned SQL query, there are two parameters:
- revision_number
-
The first parameter marks the revision number we are interested in or the latest one that exists up to this particular revision.
- revision_type
-
The second parameter specifies that we are not interested in
DEL
RevisionType
so that deleted entries are filtered out.
The same goes for the second revision associated with the UPDATE
statement.
Example 648. Getting the second revision for the Customer
entity
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(1))
.getSingleResult();
assertEquals("Doe Jr.", customer.getLastName());
For the deleted entity revision, Envers throws a NoResultException
since the entity was no longer valid at that revision.
Example 649. Getting the third revision for the Customer
entity
try {
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(2))
.getSingleResult();
fail("The Customer was deleted at this revision: " + revisions.get(2));
}
catch (NoResultException expected) {
}
Example 650. Getting the third revision for the Customer
entity without getting a NoResultException
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(
Customer.class,
Customer.class.getName(),
revisions.get(2),
true)
.getSingleResult();
assertEquals(Long.valueOf(1L), customer.getId());
assertNull(customer.getFirstName());
assertNull(customer.getLastName());
assertNull(customer.getCreatedOn());
See the Javadocs for details on other functionality offered.
21.2. Configuration Properties
It is possible to configure various aspects of Hibernate Envers behavior, such as table names, etc.
org.hibernate.envers.audit_table_prefix
-
String that will be prepended to the name of an audited entity to create the name of the entity and that will hold audit information.
org.hibernate.envers.audit_table_suffix
(default:_AUD
)-
String that will be appended to the name of an audited entity to create the name of the entity and that will hold audit information.
If you audit an entity with a table name Person, in the default setting Envers will generate a
Person_AUD
table to store historical data. org.hibernate.envers.revision_field_name
(default:REV
)-
Name of a field in the audit entity that will hold the revision number.
org.hibernate.envers.revision_type_field_name
(default:REVTYPE
)-
Name of a field in the audit entity that will hold the type of the revision (currently, this can be:
add
,mod
,del
). org.hibernate.envers.revision_on_collection_change
(default:true
)-
Should a revision be generated when a not-owned relation field changes (this can be either a collection in a one-to-many relation or the field using
mappedBy
attribute in a one-to-one relation). org.hibernate.envers.do_not_audit_optimistic_locking_field
(default:true
)-
When true, properties to be used for optimistic locking, annotated with
@Version
, will not be automatically audited (their history won’t be stored; it normally doesn’t make sense to store it). org.hibernate.envers.store_data_at_delete
(default:false
)-
Should the entity data be stored in the revision when the entity is deleted (instead of only storing the id and all other properties as null).
This is not normally needed, as the data is present in the last-but-one revision.
Sometimes, however, it is easier and more efficient to access it in the last revision (then the data that the entity contained before deletion is stored twice). org.hibernate.envers.default_schema
(default:null
— same schema as the table being audited)-
The default schema name that should be used for audit tables.
Can be overridden using the
@AuditTable( schema = "…" )
annotation.If not present, the schema will be the same as the schema of the table being audited.
org.hibernate.envers.default_catalog
(default:null
— same catalog as the table being audited)-
The default catalog name that should be used for audit tables.
Can be overridden using the
@AuditTable( catalog = "…" )
annotation.If not present, the catalog will be the same as the catalog of the normal tables.
org.hibernate.envers.audit_strategy
(default:org.hibernate.envers.strategy.DefaultAuditStrategy
)-
The audit strategy that should be used when persisting audit data.
The default stores only the revision, at which an entity was modified.An alternative, the
org.hibernate.envers.strategy.ValidityAuditStrategy
stores both the start revision and the end revision.
Together these define when an audit row was valid, hence the name ValidityAuditStrategy. org.hibernate.envers.audit_strategy_validity_end_rev_field_name
(default:REVEND
)-
The column name that will hold the end revision number in audit entities.
This property is only valid if the validity audit strategy is used. org.hibernate.envers.audit_strategy_validity_store_revend_timestamp
(default:false
)-
Should the timestamp of the end revision be stored, until which the data was valid, in addition to the end revision itself.
This is useful to be able to purge old Audit records out of a relational database by using table partitioning.Partitioning requires a column that exists within the table.
This property is only evaluated if theValidityAuditStrategy
is used. org.hibernate.envers.audit_strategy_validity_revend_timestamp_field_name
(default:REVEND_TSTMP
)-
Column name of the timestamp of the end revision until which the data was valid.
Only used if theValidityAuditStrategy
is used, andorg.hibernate.envers.audit_strategy_validity_store_revend_timestamp
evaluates to true. org.hibernate.envers.audit_strategy_validity_revend_timestamp_numeric
(default:false
)-
Boolean flag that controls whether the revision end timestamp field is treated as a
Long
data type.
Only used if theValidityAuditStrategy
is used, andorg.hibernate.envers.audit_strategy_validity_store_revend_timestamp
evaluates to true. org.hibernate.envers.audit_strategy_validity_revend_timestamp_legacy_placement
(default:true
)-
Boolean flag that controls whether the revision end timestamp field is propagated to the joined subclass audit tables.
Only used if theValidityAuditStrategy
is used, andorg.hibernate.envers.audit_strategy_validity_store_revend_timestamp
evaluates to true.When set to
true
, the legacy mapping behavior is used such that the revision end timestamp is only maintained in the root entity audit table.
When set tofalse
, the revision end timestamp is maintained in both the root entity and joined subclass audit tables; allowing the potential to apply database partitioning to the joined subclass tables just like the root entity audit tables. org.hibernate.envers.use_revision_entity_with_native_id
(default:true
)-
Boolean flag that determines the strategy of revision number generation.
Default implementation of revision entity uses native identifier generator.If the current database engine does not support identity columns, users are advised to set this property to false.
In this case revision numbers are created by preconfigured
org.hibernate.id.enhanced.SequenceStyleGenerator
.
See:org.hibernate.envers.DefaultRevisionEntity
andorg.hibernate.envers.enhanced.SequenceIdRevisionEntity
. org.hibernate.envers.track_entities_changed_in_revision
(default:false
)-
Should entity types, that have been modified during each revision, be tracked.
The default implementation createsREVCHANGES
table that stores entity names of modified persistent objects.
Single record encapsulates the revision identifier (foreign key toREVINFO
table) and a string value.
For more information, refer to Tracking entity names modified during revisions and Querying for entity types modified in a given revision. org.hibernate.envers.global_with_modified_flag
(default:false
, can be individually overridden with@Audited( withModifiedFlag = true )
)-
Should property modification flags be stored for all audited entities and all properties.
When set to true, for all properties an additional boolean column in the audit tables will be created, filled with information if the given property changed in the given revision.
When set to false, such column can be added to selected entities or properties using the
@Audited
annotation.For more information, refer to Tracking entity changes at the property level and Querying for entity revisions that modified a given property.
org.hibernate.envers.modified_flag_suffix
(default:_MOD
)-
The suffix for columns storing «Modified Flags».
For example, a property called «age», will by default get modified flag with column name «age_MOD».
org.hibernate.envers.modified_column_naming_strategy
(default:org.hibernate.envers.boot.internal.LegacyModifiedColumnNamingStrategy
)-
The naming strategy to be used for modified flag columns in the audit metadata.
org.hibernate.envers.embeddable_set_ordinal_field_name
(default:SETORDINAL
)-
Name of column used for storing ordinal of the change in sets of embeddable elements.
org.hibernate.envers.cascade_delete_revision
(default:false
)-
While deleting revision entry, remove data of associated audited entities. Requires database support for cascade row removal.
org.hibernate.envers.allow_identifier_reuse
(default:false
)-
Guarantees proper validity audit strategy behavior when application reuses identifiers of deleted entities. Exactly one row with
null
end date exists for each identifier. org.hibernate.envers.original_id_prop_name
(default:originalId
)-
Specifies the composite-id key property name used by the audit table mappings.
org.hibernate.envers.find_by_revision_exact_match
(default:false
)-
Specifies whether or not
AuditReader#find
methods which accept a revision-number argument are to find results based on fuzzy-match or exact-match behavior.The old (legacy) behavior has always been to perform a fuzzy-match where these methods would return a match if any revision existed for the primary-key with a revision-number less-than or equal-to the revision method argument.
This behavior is great when you want to find the snapshot of a non-related entity based on another entity’s revision number.The new (optional) behavior when this option is enabled forces the query to perform an exact-match instead.
In order for these methods to return a non-null
value, a revision entry must exist for the entity with the specified primary key and revision number; otherwise the result will benull
. org.hibernate.envers.global_relation_not_found_legacy_flag
(default:true
)-
Globally defines whether legacy relation not-found behavior should be used or not.
By specifying
true
, anyEntityNotFoundException
errors will be thrown unless theAudited
annotation explicitly specifies to ignore not-found relations.
By specifyingfalse
, anyEntityNotFoundException
will be be ignored unless theAudited
annotation explicitly specifies to raise the error rather than silently ignore not-found relations.
The following configuration options have been added recently and should be regarded as experimental:
|
21.3. Additional mapping annotations
The name of the audit table can be set on a per-entity basis, using the @AuditTable
annotation.
It may be tedious to add this annotation to every audited entity, so if possible, it’s better to use a prefix/suffix.
If you have a mapping with secondary tables, audit tables for them will be generated in the same way (by adding the prefix and suffix).
If you wish to overwrite this behavior, you can use the @SecondaryAuditTable
and @SecondaryAuditTables
annotations.
If you have a mapping with collection tables, the audit table for them will be generated in the same way (by using the prefix and suffix).
If you wish to overwrite this behavior, you can use the @CollectionAuditTable
annotations.
If you’d like to override auditing behavior of some fields/properties inherited from @MappedSuperclass
or in an embedded component,
you can apply the @AuditOverride
annotation on the subtype or usage site of the component.
If you want to audit a relation mapped with @OneToMany
and @JoinColumn
,
please see Mapping exceptions for a description of the additional @AuditJoinTable
annotation that you’ll probably want to use.
If you want to audit a relation, where the target entity is not audited (that is the case for example with dictionary-like entities, which don’t change and don’t have to be audited),
just annotate it with @Audited( targetAuditMode = RelationTargetAuditMode.NOT_AUDITED )
.
Then, while reading historic versions of your entity, the relation will always point to the «current» related entity.
By default Envers throws jakarta.persistence.EntityNotFoundException
when «current» entity does not exist in the database.
Apply @NotFound( action = NotFoundAction.IGNORE )
annotation to silence the exception and assign null value instead.
The hereby solution causes implicit eager loading of to-one relations.
If you’d like to audit properties of a superclass of an entity, which are not explicitly audited (they don’t have the @Audited
annotation on any properties or on the class),
you can set the @AuditOverride( forClass = SomeEntity.class, isAudited = true/false )
annotation.
The |
21.4. Choosing an audit strategy
After the basic configuration, it is important to choose the audit strategy that will be used to persist and retrieve audit information.
There is a trade-off between the performance of persisting and the performance of querying the audit information.
Currently, there are two audit strategies.
-
The default audit strategy persists the audit data together with a start revision.
For each row inserted, updated or deleted in an audited table, one or more rows are inserted in the audit tables, together with the start revision of its validity.
Rows in the audit tables are never updated after insertion.
Queries of audit information use subqueries to select the applicable rows in the audit tables.These subqueries are notoriously slow and difficult to index. -
The alternative is a validity audit strategy.
This strategy stores the start-revision and the end-revision of audit information.
For each row inserted, updated or deleted in an audited table, one or more rows are inserted in the audit tables, together with the start revision of its validity.
But at the same time, the end-revision field of the previous audit rows (if available) is set to this revision.
Queries on the audit information can then use ‘between start and end revision’ instead of subqueries as used by the default audit strategy.The consequence of this strategy is that persisting audit information will be a bit slower because of the extra updates involved,
but retrieving audit information will be a lot faster.This can be improved even further by adding extra indexes.
21.4.1. Configuring the ValidityAuditStrategy
To better visualize how the ValidityAuditStrategy
works, consider the following exercise where
we replay the previous audit logging example for the Customer
entity.
First, you need to configure the ValidityAuditStrategy
:
Example 651. Configuring the ValidityAuditStrategy
options.put(
EnversSettings.AUDIT_STRATEGY,
ValidityAuditStrategy.class.getName()
);
If, you’re using the persistence.xml
configuration file,
then the mapping will look as follows:
<property
name="org.hibernate.envers.audit_strategy"
value="org.hibernate.envers.strategy.ValidityAuditStrategy"
/>
Once you configured the ValidityAuditStrategy
, the following schema is going to be automatically generated:
Example 652. Envers schema for the ValidityAuditStrategy
create table Customer (
id bigint not null,
created_on timestamp,
firstName varchar(255),
lastName varchar(255),
primary key (id)
)
create table Customer_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint,
REVEND integer,
created_on timestamp,
firstName varchar(255),
lastName varchar(255),
primary key (id, REV)
)
create table REVINFO (
REV integer generated by default as identity,
REVTSTMP bigint,
primary key (REV)
)
alter table Customer_AUD
add constraint FK5ecvi1a0ykunrriib7j28vpdj
foreign key (REV)
references REVINFO
alter table Customer_AUD
add constraint FKqd4fy7ww1yy95wi4wtaonre3f
foreign key (REVEND)
references REVINFO
As you can see, the REVEND
column is added as well as its foreign key to the REVINFO
table.
When rerunning the previous Customer
audit log queries against the ValidityAuditStrategy
,
we get the following results:
Example 653. Getting the first revision for the Customer
entity
select
c.id as id1_1_,
c.REV as REV2_1_,
c.REVTYPE as REVTYPE3_1_,
c.REVEND as REVEND4_1_,
c.created_on as created_5_1_,
c.firstName as firstNam6_1_,
c.lastName as lastName7_1_
from
Customer_AUD c
where
c.REV <= ?
and c.REVTYPE <> ?
and (
c.REVEND > ?
or c.REVEND is null
)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
Compared to the default strategy, the |
21.5. Revision Log
When Envers starts a new revision, it creates a new revision entity which stores information about the revision.
By default, that includes just:
- revision number
-
An integral value (
int/Integer
orlong/Long
). Essentially, the primary key of the revision.A revision number value should always be increasing and never overflows.
The default implementations provided by Envers use an
int
data type which has an upper bounds ofInteger.MAX_VALUE
.
It is critical that users consider whether this upper bounds is feasible for your application. If a large range is needed, consider using a custom revision entity mapping using along
data type.In the event that the revision number reaches its upper bounds wrapping around becoming negative, an
AuditException
will be thrown causing the current transaction to be rolled back.
This guarantees that the audit history remains in a valid state that can be queried by the Envers Query API. - revision timestamp
-
Either a
long/Long
orjava.util.Date
value representing the instant at which the revision was made.
When using ajava.util.Date
, instead of along/Long
for the revision timestamp, take care not to store it to a column data type which will lose precision.
Envers handles this information as an entity.
By default it uses its own internal class to act as the entity, mapped to the REVINFO
table.
You can, however, supply your own approach to collecting this information which might be useful to capture additional details such as who made a change
or the IP address from which the request came.
There are two things you need to make this work:
-
First, you will need to tell Envers about the entity you wish to use.
Your entity must use the@org.hibernate.envers.RevisionEntity
annotation.
It must define the two attributes described above annotated with@org.hibernate.envers.RevisionNumber
and@org.hibernate.envers.RevisionTimestamp
, respectively.
You can extend fromorg.hibernate.envers.DefaultRevisionEntity
, if you wish, to inherit all these required behaviors.Simply add the custom revision entity as you do your normal entities and Envers will find it.
It is an error for there to be multiple entities marked as @org.hibernate.envers.RevisionEntity
. -
Second, you need to tell Envers how to create instances of your revision entity which is handled by the
newRevision( Object revisionEntity )
method of theorg.hibernate.envers.RevisionListener
interface.You tell Envers your custom
org.hibernate.envers.RevisionListener
implementation to use by specifying it on the@org.hibernate.envers.RevisionEntity
annotation, using the value attribute.
If yourRevisionListener
class is inaccessible from@RevisionEntity
(e.g. it exists in a different module),
setorg.hibernate.envers.revision_listener
property to its fully qualified class name.
Class name defined by the configuration parameter overrides the revision entity’s value attribute.
Considering we have a CurrentUser
utility which stores the currently logged user:
Example 654. CurrentUser
utility
public static class CurrentUser {
public static final CurrentUser INSTANCE = new CurrentUser();
private static final ThreadLocal<String> storage = new ThreadLocal<>();
public void logIn(String user) {
storage.set(user);
}
public void logOut() {
storage.remove();
}
public String get() {
return storage.get();
}
}
Now, we need to provide a custom @RevisionEntity
to store the currently logged user
Example 655. Custom @RevisionEntity
example
@Entity(name = "CustomRevisionEntity")
@Table(name = "CUSTOM_REV_INFO")
@RevisionEntity(CustomRevisionEntityListener.class)
public static class CustomRevisionEntity extends DefaultRevisionEntity {
private String username;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
}
With the custom RevisionEntity
implementation in place,
we only need to provide the RevisionEntity
implementation which acts as a factory
of RevisionEntity
instances.
Example 656. Custom @RevisionListener
example
public static class CustomRevisionEntityListener implements RevisionListener {
public void newRevision(Object revisionEntity) {
CustomRevisionEntity customRevisionEntity =
(CustomRevisionEntity) revisionEntity;
customRevisionEntity.setUsername(
CurrentUser.INSTANCE.get()
);
}
}
When generating the database schema, Envers creates the following RevisionEntity
table:
Example 657. Auto-generated RevisionEntity
Envers table
create table CUSTOM_REV_INFO (
id integer not null,
timestamp bigint not null,
username varchar(255),
primary key (id)
)
You can see the username
column in place.
Now, when inserting a Customer
entity, Envers generates the following statements:
Example 658. Auditing using the custom @RevisionEntity
instance
CurrentUser.INSTANCE.logIn("Vlad Mihalcea");
scope.inTransaction( entityManager -> {
Customer customer = new Customer();
customer.setId(1L);
customer.setFirstName("John");
customer.setLastName("Doe");
entityManager.persist(customer);
});
CurrentUser.INSTANCE.logOut();
insert
into
Customer
(created_on, firstName, lastName, id)
values
(?, ?, ?, ?)
-- binding parameter [1] as [TIMESTAMP] - [Thu Jul 27 15:45:00 EEST 2017]
-- binding parameter [2] as [VARCHAR] - [John]
-- binding parameter [3] as [VARCHAR] - [Doe]
-- binding parameter [4] as [BIGINT] - [1]
insert
into
CUSTOM_REV_INFO
(timestamp, username, id)
values
(?, ?, ?)
-- binding parameter [1] as [BIGINT] - [1501159500888]
-- binding parameter [2] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [3] as [INTEGER] - [1]
insert
into
Customer_AUD
(REVTYPE, created_on, firstName, lastName, id, REV)
values
(?, ?, ?, ?, ?, ?)
-- binding parameter [1] as [INTEGER] - [0]
-- binding parameter [2] as [TIMESTAMP] - [Thu Jul 27 15:45:00 EEST 2017]
-- binding parameter [3] as [VARCHAR] - [John]
-- binding parameter [4] as [VARCHAR] - [Doe]
-- binding parameter [5] as [BIGINT] - [1]
-- binding parameter [6] as [INTEGER] - [1]
As demonstrated by the example above, the username is properly set and propagated to the CUSTOM_REV_INFO
table.
This strategy is deprecated since version 5.2. The alternative is to use dependency injection offered as of version 5.3. An alternative method to using the The method accepts a
|
As of Hibernate Envers 5.3, dependency injection is now supported for a This feature is up to the various dependency frameworks, such as CDI and Spring, to supply the |
21.6. Tracking entity names modified during revisions
By default, entity types that have been changed in each revision are not being tracked.
This implies the necessity to query all tables storing audited data in order to retrieve changes made during the specified revision.
Envers provides a simple mechanism that creates REVCHANGES
table which stores entity names of modified persistent objects.
Single record encapsulates the revision identifier (foreign key to REVINFO
table) and a string value.
Tracking of modified entity names can be enabled in three different ways:
-
Set
org.hibernate.envers.track_entities_changed_in_revision
parameter totrue
.
In this caseorg.hibernate.envers.DefaultTrackingModifiedEntitiesRevisionEntity
will be implicitly used as the revision log entity. -
Create a custom revision entity that extends
org.hibernate.envers.DefaultTrackingModifiedEntitiesRevisionEntity
class.@Entity(name = "CustomTrackingRevisionEntity") @Table(name = "TRACKING_REV_INFO") @RevisionEntity public static class CustomTrackingRevisionEntity extends DefaultTrackingModifiedEntitiesRevisionEntity { }
-
Mark an appropriate field of a custom revision entity with
@org.hibernate.envers.ModifiedEntityNames
annotation.
The property is required to be ofSet<String>
type.@Entity(name = "CustomTrackingRevisionEntity") @Table(name = "TRACKING_REV_INFO") @RevisionEntity public static class CustomTrackingRevisionEntity extends DefaultRevisionEntity { @ElementCollection @JoinTable( name = "REVCHANGES", joinColumns = @JoinColumn(name = "REV") ) @Column(name = "ENTITYNAME") @ModifiedEntityNames private Set<String> modifiedEntityNames = new HashSet<>(); public Set<String> getModifiedEntityNames() { return modifiedEntityNames; } }
Considering we have a Customer
entity illustrated by the following example:
Example 659. Customer
entity before renaming
@Audited
@Entity(name = "Customer")
public static class Customer {
@Id
private Long id;
private String firstName;
private String lastName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_on")
@CreationTimestamp
private Date createdOn;
//Getters and setters are omitted for brevity
}
If the Customer
entity class name is changed to ApplicationCustomer
,
Envers is going to insert a new record in the REVCHANGES
table with the previous entity class name:
Example 660. Customer
entity after renaming
@Audited
@Entity(name = "Customer")
public static class ApplicationCustomer {
@Id
private Long id;
private String firstName;
private String lastName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_on")
@CreationTimestamp
private Date createdOn;
//Getters and setters are omitted for brevity
}
insert
into
REVCHANGES
(REV, ENTITYNAME)
values
(?, ?)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [VARCHAR] - [org.hibernate.userguide.envers.EntityTypeChangeAuditTest$Customer]
Users, that have chosen one of the approaches listed above,
can retrieve all entities modified in a specified revision by utilizing API described in Querying for entity types modified in a given revision.
Users are also allowed to implement custom mechanisms of tracking modified entity types.
In this case, they shall pass their own implementation of org.hibernate.envers.EntityTrackingRevisionListener
interface as the value of @org.hibernate.envers.RevisionEntity
annotation.
EntityTrackingRevisionListener
interface exposes one method that notifies whenever audited entity instance has been
added, modified or removed within current revision boundaries.
Example 661. The EntityTrackingRevisionListener
implementation
public static class CustomTrackingRevisionListener implements EntityTrackingRevisionListener {
@Override
public void entityChanged(Class entityClass,
String entityName,
Object entityId,
RevisionType revisionType,
Object revisionEntity) {
String type = entityClass.getName();
((CustomTrackingRevisionEntity) revisionEntity).addModifiedEntityType(type);
}
@Override
public void newRevision(Object revisionEntity) {
}
}
The CustomTrackingRevisionListener
adds the fully-qualified class name to the modifiedEntityTypes
attribute of the CustomTrackingRevisionEntity
.
Example 662. The RevisionEntity
using the custom EntityTrackingRevisionListener
@Entity(name = "CustomTrackingRevisionEntity")
@Table(name = "TRACKING_REV_INFO")
@RevisionEntity(CustomTrackingRevisionListener.class)
public static class CustomTrackingRevisionEntity {
@Id
@GeneratedValue
@RevisionNumber
private int customId;
@RevisionTimestamp
private long customTimestamp;
@OneToMany(
mappedBy="revision",
cascade={
CascadeType.PERSIST,
CascadeType.REMOVE
}
)
private Set<EntityType> modifiedEntityTypes = new HashSet<>();
public Set<EntityType> getModifiedEntityTypes() {
return modifiedEntityTypes;
}
public void addModifiedEntityType(String entityClassName) {
modifiedEntityTypes.add(new EntityType(this, entityClassName));
}
}
The CustomTrackingRevisionEntity
contains a @OneToMany
list of ModifiedTypeRevisionEntity
Example 663. The EntityType
encapsulates the entity type name before a class name modification
@Entity(name = "EntityType")
public static class EntityType {
@Id
@GeneratedValue
private Integer id;
@ManyToOne
private CustomTrackingRevisionEntity revision;
private String entityClassName;
private EntityType() {
}
public EntityType(CustomTrackingRevisionEntity revision, String entityClassName) {
this.revision = revision;
this.entityClassName = entityClassName;
}
//Getters and setters are omitted for brevity
}
Now, when fetching the CustomTrackingRevisionEntity
, you can get access to the previous entity class name.
Example 664. Getting the EntityType
through the CustomTrackingRevisionEntity
AuditReader auditReader = AuditReaderFactory.get(entityManager);
List<Number> revisions = auditReader.getRevisions(
ApplicationCustomer.class,
1L
);
CustomTrackingRevisionEntity revEntity = auditReader.findRevision(
CustomTrackingRevisionEntity.class,
revisions.get(0)
);
Set<EntityType> modifiedEntityTypes = revEntity.getModifiedEntityTypes();
assertEquals(1, modifiedEntityTypes.size());
EntityType entityType = modifiedEntityTypes.iterator().next();
assertEquals(
Customer.class.getName(),
entityType.getEntityClassName()
);
21.7. Tracking entity changes at the property level
By default, the only information stored by Envers are revisions of modified entities.
This approach lets users create audit queries based on historical values of entity properties.
Sometimes it is useful to store additional metadata for each revision, when you are interested also in the type of changes, not only about the resulting values.
The feature described in Tracking entity names modified during revisions makes it possible to tell which entities were modified in a given revision.
The feature described here takes it one step further.
Modification Flags enable Envers to track which properties of audited entities were modified in a given revision.
Tracking entity changes at the property level can be enabled by:
-
setting
org.hibernate.envers.global_with_modified_flag
configuration property totrue
.
This global switch will cause adding modification flags to be stored for all audited properties of all audited entities. -
using
@Audited( withModifiedFlag = true )
on a property or on an entity.
The trade-off coming with this functionality is an increased size of audit tables and a very little, almost negligible, performance drop during audit writes.
This is due to the fact that every tracked property has to have an accompanying boolean column in the schema that stores information about the property modifications.
Of course, it is Enver’s job to fill these columns accordingly — no additional work by the developer is required.
Because of costs mentioned, it is recommended to enable the feature selectively, when needed with use of the granular configuration means described above.
Example 665. Mapping for tracking entity changes at the property level
@Audited(withModifiedFlag = true)
@Entity(name = "Customer")
public static class Customer {
@Id
private Long id;
private String firstName;
private String lastName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_on")
@CreationTimestamp
private Date createdOn;
//Getters and setters are omitted for brevity
}
create table Customer_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint,
created_on timestamp,
createdOn_MOD boolean,
firstName varchar(255),
firstName_MOD boolean,
lastName varchar(255),
lastName_MOD boolean,
primary key (id, REV)
)
As you can see, every property features a _MOD
column (e.g. createdOn_MOD
) in the audit log.
Example 666. Tracking entity changes at the property level example
Customer customer = entityManager.find(Customer.class, 1L);
customer.setLastName("Doe Jr.");
update
Customer
set
created_on = ?,
firstName = ?,
lastName = ?
where
id = ?
-- binding parameter [1] as [TIMESTAMP] - [2017-07-31 15:58:20.342]
-- binding parameter [2] as [VARCHAR] - [John]
-- binding parameter [3] as [VARCHAR] - [Doe Jr.]
-- binding parameter [4] as [BIGINT] - [1]
insert
into
REVINFO
(REV, REVTSTMP)
values
(null, ?)
-- binding parameter [1] as [BIGINT] - [1501505900439]
insert
into
Customer_AUD
(REVTYPE, created_on, createdOn_MOD, firstName, firstName_MOD, lastName, lastName_MOD, id, REV)
values
(?, ?, ?, ?, ?, ?, ?, ?, ?)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [TIMESTAMP] - [2017-07-31 15:58:20.342]
-- binding parameter [3] as [BOOLEAN] - [false]
-- binding parameter [4] as [VARCHAR] - [John]
-- binding parameter [5] as [BOOLEAN] - [false]
-- binding parameter [6] as [VARCHAR] - [Doe Jr.]
-- binding parameter [7] as [BOOLEAN] - [true]
-- binding parameter [8] as [BIGINT] - [1]
-- binding parameter [9] as [INTEGER] - [2]
To see how «Modified Flags» can be utilized, check out the very simple query API that uses them: Querying for entity revisions that modified a given property.
21.8. Selecting strategy for tracking property level changes
By default, Envers uses the legacy
modified column naming strategy.
This strategy is designed to add columns based on the following rule-set:
-
If property is annotated with
@Audited
and the modifiedColumnName attribute is specified, the column will directly be based on the supplied name. -
If property is not annotated with
@Audited
or if no modifiedColumnName attribute is given, the column will be named after the java class property, appended with the configured suffix, the default being_MOD
.
While this strategy has no performance drawbacks, it does present concerns for users who prefer consistency without verbosity.
Lets take the following entity mapping as an example.
@Audited(withModifiedFlags = true)
@Entity
public class Customer {
@Id
private Integer id;
@Column(name = "customer_name")
private String name;
}
This mapping will actually lead to some inconsistent naming between columns, see below for how the model’s name will be stored in customer_name
but the modified column that tracks whether this column changes between revisions is named name_MOD
.
CREATE TABLE Customer_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint not null,
customer_name varchar(255),
name_MOD boolean,
primary key(id, REV)
)
An additional strategy called improved
, aims to address these inconsistent column naming concerns.
This strategy uses the following rule-set:
-
Property is a Basic type (Single Column valued property)
-
Use the modifiedColumnName directly if one is supplied on the property mapping
-
Otherwise use the resolved ORM column name appended with the modified flag suffix configured value
-
-
Property is an Association (to-one mapping) with a Foreign Key using a single column
-
Use the modifiedColumnName directly if one is supplied on the property mapping
-
Otherwise use the resolved ORM column name appended with the modified flag suffix configured value
-
-
Property is an Association (to-one mapping) with a Foreign Key using multiple columns
-
Use the modifiedColumnName directly if one is supplied on the property mapping
-
Otherwise use the property name appended with the modified flag suffix configured value
-
-
Property is an Embeddable
-
Use the modifiedColumnName directly if one is supplied on the property mapping
-
Otherwise use the property name appended with the modified flag suffix configured value
-
While using this strategy, the same Customer
mapping will generate the following table schema:
CREATE TABLE Customer_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint not null,
customer_name varchar(255),
customer_name_MOD boolean,
primary key(id, REV)
)
When already using Envers in conjunction with the modified columns flag feature, it is advised not to enable the new strategy immediately as schema changes would be required.
You will need to either migrate your existing schema manually to adhere to the rules above or use the explicit modifiedColumnName attribute on the @Audited
annotation for existing columns that use the feature.
To configure a custom strategy implementation or use the improved strategy, the configuration option org.hibernate.envers.modified_column_naming_strategy
will need to be set.
This option can be the fully qualified class name of a ModifiedColumnNameStrategy
implementation or legacy
or improved
for either of the two provided implementations.
21.9. Queries
You can think of historic data as having two dimensions:
- horizontal
-
The state of the database at a given revision. Thus, you can query for entities as they were at revision N.
- vertical
-
The revisions, at which entities changed. Hence, you can query for revisions, in which a given entity changed.
The queries in Envers are similar to Hibernate Criteria queries, so if you are familiar with them, using Envers queries will be much easier.
The main limitation of the current queries implementation is that you cannot traverse relations.
You can only specify constraints on the ids of the related entities, and only on the «owning» side of the relation.
This, however, will be changed in future releases.
The queries on the audited data will be in many cases much slower than corresponding queries on «live» data, Queries are improved both in terms of speed and possibilities when using the validity audit strategy, |
21.10. Querying for entities of a class at a given revision
The entry point for this type of queries is:
Example 667. Getting the Customer
entity at a given revision
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(0))
.getSingleResult();
assertEquals("Doe", customer.getLastName());
21.11. Querying for entities using filtering criteria
You can then specify constraints, which should be met by the entities returned, by adding restrictions,
which can be obtained using the AuditEntity
factory class.
For example, to select only entities where the firstName
property is equal to «John»:
Example 668. Getting the Customer
audit log with a given firstName
attribute value
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.property("firstName").eq("John"))
.getResultList();
assertEquals(2, customers.size());
assertEquals("Doe", customers.get(0).getLastName());
assertEquals("Doe Jr.", customers.get(1).getLastName());
And, to select only entities whose relationships are related to a given entity,
you can use either the target entity or its identifier.
Example 669. Getting the Customer
entities whose address
attribute matches the given entity reference
Address address = entityManager.getReference(Address.class, 1L);
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.property("address").eq(address))
.getResultList();
assertEquals(2, customers.size());
select
c.id as id1_3_,
c.REV as REV2_3_,
c.REVTYPE as REVTYPE3_3_,
c.REVEND as REVEND4_3_,
c.created_on as created_5_3_,
c.firstName as firstNam6_3_,
c.lastName as lastName7_3_,
c.address_id as address_8_3_
from
Customer_AUD c
where
c.address_id = ?
order by
c.REV asc
-- binding parameter [1] as [BIGINT] - [1]
The same SQL is generated even if we provide the identifier instead of the target entity reference.
Example 670. Getting the Customer
entities whose address
identifier matches the given entity identifier
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.relatedId("address").eq(1L))
.getResultList();
assertEquals(2, customers.size());
Apart from strict equality matching, you can also use an IN
clause to provide multiple entity identifiers:
Example 671. Getting the Customer
entities whose address
identifier matches one of the given entity identifiers
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.relatedId("address").in(new Object[] { 1L, 2L }))
.getResultList();
assertEquals(2, customers.size());
select
c.id as id1_3_,
c.REV as REV2_3_,
c.REVTYPE as REVTYPE3_3_,
c.REVEND as REVEND4_3_,
c.created_on as created_5_3_,
c.firstName as firstNam6_3_,
c.lastName as lastName7_3_,
c.address_id as address_8_3_
from
Customer_AUD c
where
c.address_id in (
? , ?
)
order by
c.REV asc
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [BIGINT] - [2]
You can limit the number of results, order them, and set aggregations and projections (except grouping) in the usual way.
When your query is complete, you can obtain the results by calling the getSingleResult()
or getResultList()
methods.
A full query, can look for example like this:
Example 672. Getting the Customer
entities using filtering and pagination
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.addOrder(AuditEntity.property("lastName").desc())
.add(AuditEntity.relatedId("address").eq(1L))
.setFirstResult(1)
.setMaxResults(2)
.getResultList();
assertEquals(1, customers.size());
select
c.id as id1_3_,
c.REV as REV2_3_,
c.REVTYPE as REVTYPE3_3_,
c.REVEND as REVEND4_3_,
c.created_on as created_5_3_,
c.firstName as firstNam6_3_,
c.lastName as lastName7_3_,
c.address_id as address_8_3_
from
Customer_AUD c
where
c.address_id = ?
order by
c.lastName desc
limit ?
offset ?
21.12. Querying for revisions, at which entities of a given class changed
The entry point for this type of queries is:
AuditQuery query = AuditReaderFactory.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true);
You can add constraints to this query in the same way as to the previous one.
There are some additional possibilities:
-
using
AuditEntity.revisionNumber()
you can specify constraints, projections and order on the revision number, in which the audited entity was modified. -
similarly, using
AuditEntity.revisionProperty( propertyName )
you can specify constraints, projections and order on a property of the revision entity,
corresponding to the revision in which the audited entity was modified. -
AuditEntity.revisionType()
gives you access as above to the type of the revision (ADD
,MOD
,DEL
).
Using these methods, you can order the query results by revision number, set projection or constraint the revision number to be greater or less than a specified value, etc.
For example, the following query will select the smallest revision number, at which entity of class MyEntity
with id entityId
has changed, after revision number 2:
Number revision = (Number) AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.addProjection(AuditEntity.revisionNumber().min())
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.revisionNumber().gt(2))
.getSingleResult();
The second additional feature you can use in queries for revisions is the ability to maximize/minimize a property.
For example, if you want to select the smallest possible revision at which the value of the createdOn
attribute was larger then a given value,
you can run the following query:
Number revision = (Number) AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.addProjection(AuditEntity.revisionNumber().min())
.add(AuditEntity.id().eq(1L))
.add(
AuditEntity.property("createdOn")
.minimize()
.add(AuditEntity.property("createdOn")
.ge(
Timestamp.from(
LocalDateTime.now()
.minusDays(1)
.toInstant(ZoneOffset.UTC)
)
)
)
)
.getSingleResult();
The minimize()
and maximize()
methods return a criterion, to which you can add constraints,
which must be met by the entities with the maximized/minimized properties.
You probably also noticed that there are two boolean parameters, passed when creating the query.
selectEntitiesOnly
-
The first parameter is only valid when you don’t set an explicit projection.
If true, the result of the query will be a list of entities (which changed at revisions satisfying the specified constraints).
If false, the result will be a list of three element arrays:
-
the first element will be the changed entity instance.
-
the second will be an entity containing revision data (if no custom entity is used, this will be an instance of
DefaultRevisionEntity
). -
the third will be the type of the revision (one of the values of the
RevisionType
enumeration:ADD
,MOD
,DEL
).
-
selectDeletedEntities
-
The second parameter specifies if revisions,
in which the entity was deleted should be included in the results.If yes, such entities will have the revision type
DEL
and all attributes, except theid
, will be set tonull
.
Another useful feature is AggregatedAuditExpression#computeAggregationInInstanceContext()
. This can be used to create
an aggregate query based on the entity instance primary key.
For example, if you wanted to locate all customers but only wanted to retrieve the instances with the
maximum revision number, you would use the following query:
List<Customer> results = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, false)
.add(AuditEntity.revisionNumber().maximize().computeAggregationInInstanceContext())
.getResultList();
In other words, the result set would contain a list of Customer
instances, one per primary key. Each instance would
hold the audited property data at the maximum revision number for each Customer
primary key.
21.13. Querying for entity revisions that modified a given property
For the two types of queries described above it’s possible to use special Audit
criteria called hasChanged()
and hasNotChanged()
that make use of the functionality described in Tracking entity changes at the property level.
Let’s have a look at various queries that can benefit from these two criteria.
First, you must make sure that your entity can track modification flags:
Example 673. Valid only when audit logging tracks entity attribute modification flags
@Audited(withModifiedFlag = true)
The following query will return all revisions of the Customer
entity with the given id
,
for which the lastName
property has changed.
Example 674. Getting all Customer
revisions for which the lastName
attribute has changed
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.property("lastName").hasChanged())
.getResultList();
select
c.id as id1_3_0_,
c.REV as REV2_3_0_,
defaultrev1_.REV as REV1_4_1_,
c.REVTYPE as REVTYPE3_3_0_,
c.REVEND as REVEND4_3_0_,
c.created_on as created_5_3_0_,
c.createdOn_MOD as createdO6_3_0_,
c.firstName as firstNam7_3_0_,
c.firstName_MOD as firstNam8_3_0_,
c.lastName as lastName9_3_0_,
c.lastName_MOD as lastNam10_3_0_,
c.address_id as address11_3_0_,
c.address_MOD as address12_3_0_,
defaultrev1_.REVTSTMP as REVTSTMP2_4_1_
from
Customer_AUD c cross
join
REVINFO defaultrev1_
where
c.id = ?
and c.lastName_MOD = ?
and c.REV=defaultrev1_.REV
order by
c.REV asc
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [BOOLEAN] - [true]
Using this query we won’t get all other revisions in which lastName
wasn’t touched.
From the SQL query you can see that the lastName_MOD
column is being used in the WHERE clause,
hence the aforementioned requirement for tracking modification flags.
Of course, nothing prevents users from combining hasChanged
condition with some additional criteria.
Example 675. Getting all Customer
revisions for which the lastName
attribute has changed and the firstName
attribute has not changed
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.property("lastName").hasChanged())
.add(AuditEntity.property("firstName").hasNotChanged())
.getResultList();
select
c.id as id1_3_0_,
c.REV as REV2_3_0_,
defaultrev1_.REV as REV1_4_1_,
c.REVTYPE as REVTYPE3_3_0_,
c.REVEND as REVEND4_3_0_,
c.created_on as created_5_3_0_,
c.createdOn_MOD as createdO6_3_0_,
c.firstName as firstNam7_3_0_,
c.firstName_MOD as firstNam8_3_0_,
c.lastName as lastName9_3_0_,
c.lastName_MOD as lastNam10_3_0_,
c.address_id as address11_3_0_,
c.address_MOD as address12_3_0_,
defaultrev1_.REVTSTMP as REVTSTMP2_4_1_
from
Customer_AUD c cross
join
REVINFO defaultrev1_
where
c.id=?
and c.lastName_MOD=?
and c.firstName_MOD=?
and c.REV=defaultrev1_.REV
order by
c.REV asc
-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [BOOLEAN] - [true]
-- binding parameter [3] as [BOOLEAN] - [false]
To get the Customer
entities changed at a given revisionNumber
with lastName
modified and firstName
untouched,
we have to use the forEntitiesModifiedAtRevision
query:
Example 676. Getting the Customer
entity for a given revision if the lastName
attribute has changed and the firstName
attribute has not changed
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesModifiedAtRevision(Customer.class, 2)
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.property("lastName").hasChanged())
.add(AuditEntity.property("firstName").hasNotChanged())
.getSingleResult();
select
c.id as id1_3_,
c.REV as REV2_3_,
c.REVTYPE as REVTYPE3_3_,
c.REVEND as REVEND4_3_,
c.created_on as created_5_3_,
c.createdOn_MOD as createdO6_3_,
c.firstName as firstNam7_3_,
c.firstName_MOD as firstNam8_3_,
c.lastName as lastName9_3_,
c.lastName_MOD as lastNam10_3_,
c.address_id as address11_3_,
c.address_MOD as address12_3_
from
Customer_AUD c
where
c.REV=?
and c.id=?
and c.lastName_MOD=?
and c.firstName_MOD=?
-- binding parameter [1] as [INTEGER] - [2]
-- binding parameter [2] as [BIGINT] - [1]
-- binding parameter [3] as [BOOLEAN] - [true]
-- binding parameter [4] as [BOOLEAN] - [false]
21.14. Querying for revisions of entity including property names that were modified
This feature described here is still considered experimental. |
Sometimes it may be useful to query entity revisions and also determine all the properties of that revision which
were modified without having to issue multiple queries using hasChanged()
and hasNotChanged()
criteria.
You can now obtain this information easily by using the following query:
Example 677. Querying entity revisions including property names modified.
List results = AuditReaderFactory.get( entityManager )
.createQuery()
.forRevisionsOfEntityWithChanges( Customer.class, false )
.add( AuditEntity.id().eq( 1L ) )
.getResultList();
for ( Object entry : results ) {
final Object[] array = (Object[]) entry;
final Set<String> propertiesChanged = (Set<String>) array[3];
for ( String propertyName : propertiesChanged ) {
/* Do something useful with the modified property `propertyName` */
}
}
21.15. Querying for entity types modified in a given revision
The methods described below can be used only when the default mechanism of tracking changed entity types is enabled (see Tracking entity names modified during revisions). |
This basic query allows retrieving entity names and corresponding Java classes changed in a specified revision:
Example 678. Retrieving entity names and corresponding Java classes changed in a specified revision
assertEquals(
"org.hibernate.orm.test.envers.EntityTypeChangeAuditTest$Customer",
AuditReaderFactory
.get(entityManager)
.getCrossTypeRevisionChangesReader()
.findEntityTypes(1)
.iterator().next()
.getFirst()
);
assertEquals(
"org.hibernate.orm.test.envers.EntityTypeChangeAuditTest$ApplicationCustomer",
AuditReaderFactory
.get(entityManager)
.getCrossTypeRevisionChangesReader()
.findEntityTypes(2)
.iterator().next()
.getFirst()
);
Other queries (also accessible from org.hibernate.envers.CrossTypeRevisionChangesReader
):
List<Object> findEntities(Number)
-
Returns snapshots of all audited entities changed (added, updated and removed) in a given revision.
ExecutesN + 1
SQL queries, whereN
is a number of different entity classes modified within specified revision. List<Object> findEntities(Number, RevisionType)
-
Returns snapshots of all audited entities changed (added, updated or removed) in a given revision filtered by modification type.
ExecutesN + 1
SQL queries, whereN
is a number of different entity classes modified within specified revision. Map<RevisionType, List<Object>> findEntitiesGroupByRevisionType(Number)
-
Returns a map containing lists of entity snapshots grouped by modification operation (e.g. addition, update and removal).
Executes3N + 1
SQL queries, whereN
is a number of different entity classes modified within specified revision.
21.16. Querying for entities using entity relation joins
Relation join queries are considered experimental and may change in future releases. |
Audit queries support the ability to apply constraints, projections, and sort operations based on entity relations. In order
to traverse entity relations through an audit query, you must use the relation traversal API with a join type.
Relation joins can be applied to |
The basis for creating an entity relation join query is as follows:
Example 679. INNER JOIN entity audit query
AuditQuery innerJoinAuditQuery = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER);
Example 680. LEFT JOIN entity audit query
AuditQuery innerJoinAuditQuery = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.LEFT);
Like any other query, constraints may be added to restrict the results.
For example, to find all Customer
entities at a given revision whose addresses are in România
,
you can use the following query:
Example 681. Filtering the join relation with a WHERE clause predicate
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER)
.add(AuditEntity.property("country").eq("România"))
.getResultList();
select
c.id as id1_3_,
c.REV as REV2_3_,
c.REVTYPE as REVTYPE3_3_,
c.REVEND as REVEND4_3_,
c.created_on as created_5_3_,
c.firstName as firstNam6_3_,
c.lastName as lastName7_3_,
c.address_id as address_8_3_
from
Customer_AUD c
inner join
Address_AUD a
on (
c.address_id=a.id
or (
c.address_id is null
)
and (
a.id is null
)
)
where
c.REV<=?
and c.REVTYPE<>?
and (
c.REVEND>?
or c.REVEND is null
)
and a.REV<=?
and a.country=?
and (
a.REVEND>?
or a.REVEND is null
)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [INTEGER] - [1]
-- binding parameter [5] as [VARCHAR] - [România]
-- binding parameter [6] as [INTEGER] - [1]
It is also possible to traverse beyond the first relation in an entity graph.
For example, to find all Customer
entities at a given revision
with the country attribute of the address property being România
:
Example 682. Filtering a nested join relation with a WHERE clause predicate
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER)
.traverseRelation("country", JoinType.INNER)
.add(AuditEntity.property("name").eq("România"))
.getResultList();
assertEquals(1, customers.size());
select
cu.id as id1_5_,
cu.REV as REV2_5_,
cu.REVTYPE as REVTYPE3_5_,
cu.REVEND as REVEND4_5_,
cu.created_on as created_5_5_,
cu.firstName as firstNam6_5_,
cu.lastName as lastName7_5_,
cu.address_id as address_8_5_
from
Customer_AUD cu
inner join
Address_AUD a
on (
cu.address_id=a.id
or (
cu.address_id is null
)
and (
a.id is null
)
)
inner join
Country_AUD co
on (
a.country_id=co.id
or (
a.country_id is null
)
and (
co.id is null
)
)
where
cu.REV<=?
and cu.REVTYPE<>?
and (
cu.REVEND>?
or cu.REVEND is null
)
and a.REV<=?
and (
a.REVEND>?
or a.REVEND is null
)
and co.REV<=?
and co.name=?
and (
co.REVEND>?
or co.REVEND is null
)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [INTEGER] - [1]
-- binding parameter [5] as [INTEGER] - [1]
-- binding parameter [6] as [INTEGER] - [1]
-- binding parameter [7] as [VARCHAR] - [România]
-- binding parameter [8] as [INTEGER] - [1]
Constraints may also be added to the properties of nested joined relations, such as testing for null
.
For example, the following query illustrates how to find all Customer
entities at a given revision
having the address
in Cluj-Napoca
or the address
does not have any country entity reference:
Example 683. Filtering a join relation using multiple predicates
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.LEFT, "a")
.add(
AuditEntity.or(
AuditEntity.property("a", "city").eq("Cluj-Napoca"),
AuditEntity.relatedId("country").eq(null)
)
)
.getResultList();
select
c.id as id1_5_,
c.REV as REV2_5_,
c.REVTYPE as REVTYPE3_5_,
c.REVEND as REVEND4_5_,
c.created_on as created_5_5_,
c.firstName as firstNam6_5_,
c.lastName as lastName7_5_,
c.address_id as address_8_5_
from
Customer_AUD c
left outer join
Address_AUD a
on (
c.address_id=a.id
or (
c.address_id is null
)
and (
a.id is null
)
)
where
c.REV<=?
and c.REVTYPE<>?
and (
c.REVEND>?
or c.REVEND is null
)
and (
a.REV is null
or a.REV<=?
and (
a.REVEND>?
or a.REVEND is null
)
)
and (
a.city=?
or a.country_id is null
)
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [INTEGER] - [1]
-- binding parameter [5] as [INTEGER] - [1]
-- binding parameter [6] as [VARCHAR] - [Cluj-Napoca]
Queries can use the |
Disjunction criterion may also be applied to relation join queries.
For example, the following query will find all Customer
entities at a given revision
where the country name is România
or that the Customer
lives in Cluj-Napoca
:
Example 684. Filtering a nested join relation using multiple predicates
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER, "a")
.traverseRelation("country", JoinType.INNER, "cn")
.up()
.up()
.add(
AuditEntity.disjunction()
.add(AuditEntity.property("a", "city").eq("Cluj-Napoca"))
.add(AuditEntity.property("cn", "name").eq("România"))
)
.addOrder(AuditEntity.property("createdOn").asc())
.getResultList();
select
cu.id as id1_5_,
cu.REV as REV2_5_,
cu.REVTYPE as REVTYPE3_5_,
cu.REVEND as REVEND4_5_,
cu.created_on as created_5_5_,
cu.firstName as firstNam6_5_,
cu.lastName as lastName7_5_,
cu.address_id as address_8_5_
from
Customer_AUD cu
inner join
Address_AUD a
on (
cu.address_id=a.id
or (
cu.address_id is null
)
and (
a.id is null
)
)
inner join
Country_AUD co
on (
a.country_id=co.id
or (
a.country_id is null
)
and (
co.id is null
)
)
where
cu.REV<=?
and cu.REVTYPE<>?
and (
cu.REVEND>?
or cu.REVEND is null
)
and (
a.city=?
or co.name=?
)
and a.REV<=?
and (
a.REVEND>?
or a.REVEND is null
)
and co.REV<=?
and (
co.REVEND>?
or co.REVEND is null
)
order by
cu.created_on asc
-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [VARCHAR] - [Cluj-Napoca]
-- binding parameter [5] as [VARCHAR] - [România]
-- binding parameter [6] as [INTEGER] - [1]
-- binding parameter [7] as [INTEGER] - [1]
-- binding parameter [8] as [INTEGER] - [1]
-- binding parameter [9] as [INTEGER] - [1]
Lastly, this example illustrates how related entity properties can be compared in a single constraint.
Assuming the Customer
and the Address
were previously changed as follows:
Example 685. Changing the Address
to match the Country
name
Customer customer = entityManager.createQuery(
"select c " +
"from Customer c " +
"join fetch c.address a " +
"join fetch a.country " +
"where c.id = :id", Customer.class)
.setParameter("id", 1L)
.getSingleResult();
customer.setLastName("Doe Sr.");
customer.getAddress().setCity(
customer.getAddress().getCountry().getName()
);
The following query shows how to find the Customer
entities
where the city
property of the address
attribute equals the name
of the associated country
attribute.
Example 686. Filtering a nested join relation using multiple predicates
List<Number> revisions = AuditReaderFactory.get(entityManager).getRevisions(
Customer.class,
1L
);
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(revisions.size() - 1))
.traverseRelation("address", JoinType.INNER, "a")
.traverseRelation("country", JoinType.INNER, "cn")
.up()
.up()
.add(AuditEntity.property("a", "city").eqProperty("cn", "name"))
.getResultList();
select
cu.id as id1_5_,
cu.REV as REV2_5_,
cu.REVTYPE as REVTYPE3_5_,
cu.REVEND as REVEND4_5_,
cu.created_on as created_5_5_,
cu.firstName as firstNam6_5_,
cu.lastName as lastName7_5_,
cu.address_id as address_8_5_
from
Customer_AUD cu
inner join
Address_AUD a
on (
cu.address_id=a.id
or (
cu.address_id is null
)
and (
a.id is null
)
)
inner join
Country_AUD cr
on (
a.country_id=cr.id
or (
a.country_id is null
)
and (
cr.id is null
)
)
where
cu.REV<=?
and cu.REVTYPE<>?
and a.city=cr.name
and (
cu.REVEND>?
or cu.REVEND is null
)
and a.REV<=?
and (
a.REVEND>?
or a.REVEND is null
)
and cr.REV<=?
and (
cr.REVEND>?
or cr.REVEND is null
)
-- binding parameter [1] as [INTEGER] - [2]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [2]
-- binding parameter [4] as [INTEGER] - [2]
-- binding parameter [5] as [INTEGER] - [2]
-- binding parameter [6] as [INTEGER] - [2]
-- binding parameter [7] as [INTEGER] - [2]
21.17. Querying for revision information without loading entities
Sometimes, it may be useful to load information about revisions to find out who performed specific revisions or
to know what entity names were modified but the change log about the related audited entities isn’t needed.
This API allows an efficient way to get the revision information entity log without instantiating the actual
entities themselves.
Here is a simple example:
AuditQuery query = getAuditReader().createQuery()
.forRevisionsOfEntity( DefaultRevisionEntity.class, true )
.add( AuditEntity.revisionNumber().between( 1, 25 ) );
This query will return all revision information entities for revisions between 1 and 25 including those which are
related to deletions. If deletions are not of interest, you would pass false
as the second argument.
Note that this query uses the DefaultRevisionEntity
class type. The class provided will vary depending on the
configuration properties used to configure Envers or if you supply your own revision entity. Typically users who
will use this API will likely be providing a custom revision entity implementation to obtain custom information
being maintained per revision.
21.18. Conditional auditing
Envers persists audit data in reaction to various Hibernate events (e.g. post update
, post insert
, and so on),
using a series of event listeners from the org.hibernate.envers.event.spi
package.
By default, if the Envers jar is in the classpath, the event listeners are auto-registered with Hibernate.
Conditional auditing can be implemented by overriding some of the Envers event listeners.
To use customized Envers event listeners, the following steps are needed:
-
Turn off automatic Envers event listeners registration by setting the
hibernate.envers.autoRegisterListeners
Hibernate property tofalse
. -
Create subclasses for appropriate event listeners.
For example, if you want to conditionally audit entity insertions, extend theorg.hibernate.envers.event.spi.EnversPostInsertEventListenerImpl
class.
Place the conditional-auditing logic in the subclasses, call the super method if auditing should be performed. -
Create your own implementation of
org.hibernate.integrator.spi.Integrator
, similar toorg.hibernate.envers.boot.internal.EnversIntegrator
.
Use your event listener classes instead of the default ones. -
For the integrator to be automatically used when Hibernate starts up, you will need to add a
META-INF/services/org.hibernate.integrator.spi.Integrator
file to your jar.
The file should contain the fully qualified name of the class implementing the interface.
The use of |
21.19. Understanding the Envers Schema
For each audited entity (that is, for each entity containing at least one audited field), an audit table is created.
By default, the audit table’s name is created by adding an «_AUD» suffix to the original table name,
but this can be overridden by specifying a different suffix/prefix in the configuration properties or per-entity using the @org.hibernate.envers.AuditTable
annotation.
The audit table contains the following columns:
- id
-
id
of the original entity (this can be more then one column in the case of composite primary keys). - revision number
-
an integer, which matches to the revision number in the revision entity table.
- revision type
-
The
org.hibernate.envers.RevisionType
enumeration ordinal stating if the change represents an INSERT, UPDATE or DELETE. - audited fields
-
properties from the original entity being audited.
The primary key of the audit table is the combination of the original id of the entity and the revision number,
so there can be at most one historic entry for a given entity instance at a given revision.
The current entity data is stored in the original table and in the audit table.
This is a duplication of data, however, as this solution makes the query system much more powerful, and as memory is cheap, hopefully, this won’t be a major drawback for the users.
A row in the audit table with entity id ID
, revision N
, and data D
means: entity with id ID
has data D
from revision N
upwards.
Hence, if we want to find an entity at revision M
, we have to search for a row in the audit table, which has the revision number smaller or equal to M
, but as large as possible.
If no such row is found, or a row with a «deleted» marker is found, it means that the entity didn’t exist at that revision.
The «revision type» field can currently have three values: 0
, 1
and 2
, which means ADD
, MOD
, and DEL
, respectively.
A row with a revision of type DEL
will only contain the id of the entity and no data (all fields NULL
), as it only serves as a marker saying «this entity was deleted at that revision».
Additionally, there is a revision entity table which contains the information about the global revision.
By default, the generated table is named REVINFO
and contains just two columns: ID
and TIMESTAMP
.
A row is inserted into this table on each new revision, that is, on each commit of a transaction, which changes audited data.
The name of this table can be configured, the name of its columns as well as adding additional columns can be achieved as discussed in Revision Log.
While global revisions are a good way to provide correct auditing of relations, some people have pointed out that this may be a bottleneck in systems where data is very often modified. One viable solution is to introduce an option to have an entity «locally revisioned», that is revisions would be created for it independently. Another possibility is to introduce a notion of «revisioning groups», which would group entities sharing the same revision numbering. Your opinions on the subject are very welcome on the forum. |
21.20. Generating Envers schema with Hibernate hbm2ddl tool
If you would like to generate the database schema file with Hibernate,
you simply need to use the hbm2ddl tool.
This task will generate the definitions of all entities, both of those which are audited by Envers and those which are not.
See the Schema generation chapter for more info.
For the following entities, Hibernate is going to generate the following database schema:
Example 687. Filtering a nested join relation using multiple predicates
@Audited
@Entity(name = "Customer")
public static class Customer {
@Id
private Long id;
private String firstName;
private String lastName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_on")
@CreationTimestamp
private Date createdOn;
@ManyToOne(fetch = FetchType.LAZY)
private Address address;
//Getters and setters omitted for brevity
}
@Audited
@Entity(name = "Address")
public static class Address {
@Id
private Long id;
@ManyToOne(fetch = FetchType.LAZY)
private Country country;
private String city;
private String street;
private String streetNumber;
//Getters and setters omitted for brevity
}
@Audited
@Entity(name = "Country")
public static class Country {
@Id
private Long id;
private String name;
//Getters and setters omitted for brevity
}
create table Address (
id bigint not null,
city varchar(255),
street varchar(255),
streetNumber varchar(255),
country_id bigint,
primary key (id)
)
create table Address_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint,
REVEND integer,
city varchar(255),
street varchar(255),
streetNumber varchar(255),
country_id bigint,
primary key (id, REV)
)
create table Country (
id bigint not null,
name varchar(255),
primary key (id)
)
create table Country_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint,
REVEND integer,
name varchar(255),
primary key (id, REV)
)
create table Customer (
id bigint not null,
created_on timestamp,
firstName varchar(255),
lastName varchar(255),
address_id bigint,
primary key (id)
)
create table Customer_AUD (
id bigint not null,
REV integer not null,
REVTYPE tinyint,
REVEND integer,
created_on timestamp,
firstName varchar(255),
lastName varchar(255),
address_id bigint,
primary key (id, REV)
)
create table REVINFO (
REV integer generated by default as identity,
REVTSTMP bigint,
primary key (REV)
)
alter table Address
add constraint FKpr4rl83u5fv832kdihl6w3kii
foreign key (country_id)
references Country
alter table Address_AUD
add constraint FKgwp5sek4pjb4awy66sp184hrv
foreign key (REV)
references REVINFO
alter table Address_AUD
add constraint FK52pqkpismfxg2b9tmwtncnk0d
foreign key (REVEND)
references REVINFO
alter table Country_AUD
add constraint FKrix4g8hm9ui6sut5sy86ujggr
foreign key (REV)
references REVINFO
alter table Country_AUD
add constraint FKpjeqmdccv22y1lbtswjb84ghi
foreign key (REVEND)
references REVINFO
alter table Customer
add constraint FKfok4ytcqy7lovuiilldbebpd9
foreign key (address_id)
references Address
alter table Customer_AUD
add constraint FK5ecvi1a0ykunrriib7j28vpdj
foreign key (REV)
references REVINFO
alter table Customer_AUD
add constraint FKqd4fy7ww1yy95wi4wtaonre3f
foreign key (REVEND)
references REVINFO
21.21. Mapping exceptions
21.21.1. What isn’t and will not be supported
Bags are not supported because they can contain non-unique elements.
Persisting a bag of `String`s violates the relational database principle that each table is a set of tuples.
In case of bags, however (which require a join table), if there is a duplicate element, the two tuples corresponding to the elements will be the same.
Although Hibernate allows this, Envers (or more precisely the database connector) will throw an exception when trying to persist two identical elements because of a unique constraint violation.
There are at least two ways out if you need bag semantics:
-
use an indexed collection, with the
@jakarta.persistence.OrderColumn
annotation. -
provide a unique id for your elements with the
@CollectionId
annotation.
21.21.2. What isn’t and will be supported
-
Bag style collections with a
@CollectionId
identifier column (see HHH-3950).
21.22. @OneToMany
with @JoinColumn
When a collection is mapped using these two annotations, Hibernate doesn’t generate a join table.
Envers, however, has to do this so that when you read the revisions in which the related entity has changed, you don’t get false results.
To be able to name the additional join table, there is a special annotation: @AuditJoinTable
, which has similar semantics to Jakarta Persistence @JoinTable
.
One special case is to have relations mapped with @OneToMany
with @JoinColumn
on the one side, and @ManyToOne
and @JoinColumn( insertable = false, updatable = false
) on the many side.
Such relations are, in fact, bidirectional, but the owning side is the collection.
To properly audit such relations with Envers, you can use the @AuditMappedBy
annotation.
It enables you to specify the reverse property (using the mappedBy
element).
In case of indexed collections, the index column must also be mapped in the referenced entity (using @Column( insertable = false, updatable = false )
, and specified using positionMappedBy
.
This annotation will affect only the way Envers works.
Please note that the annotation is experimental and may change in the future.
21.23. Advanced: Audit table partitioning
21.24. Benefits of audit table partitioning
Because audit tables tend to grow indefinitely, they can quickly become really large.
When the audit tables have grown to a certain limit (varying per RDBMS and/or operating system) it makes sense to start using table partitioning.
SQL table partitioning offers a lot of advantages including, but certainly not limited to:
-
Improved query performance by selectively moving rows to various partitions (or even purging old rows).
-
Faster data loads, index creation, etc.
21.25. Suitable columns for audit table partitioning
Generally, SQL tables must be partitioned on a column that exists within the table.
As a rule, it makes sense to use either the end revision or the end revision timestamp column for partitioning of audit tables.
End revision information is not available for the default Therefore the following Envers configuration options are required:
Optionally, you can also override the default values using following properties:
For more information, see Configuration Properties. |
The reason why the end revision information should be used for audit table partitioning is based on the assumption that audit tables should be partitioned on an ‘increasing level of relevancy’, like so:
-
A couple of partitions with audit data that is not very (or no longer) relevant.
This can be stored on slow media, and perhaps even be purged eventually. -
Some partitions for audit data that is potentially relevant.
-
One partition for audit data that is most likely to be relevant.
This should be stored on the fastest media, both for reading and writing.
21.26. Audit table partitioning example
In order to determine a suitable column for the ‘increasing level of relevancy’,
consider a simplified example of a salary registration for an unnamed agency.
Currently, the salary table contains the following rows for a certain person X:
Year | Salary (USD) |
---|---|
2006 |
3300 |
2007 |
3500 |
2008 |
4000 |
2009 |
4500 |
The salary for the current fiscal year (2010) is unknown.
The agency requires that all changes in registered salaries for a fiscal year are recorded (i.e., an audit trail).
The rationale behind this is that decisions made at a certain date are based on the registered salary at that time.
And at any time it must be possible to reproduce the reason why a certain decision was made at a certain date.
The following audit information is available, sorted in order of occurrence:
Year | Revision type | Revision timestamp | Salary (USD) | End revision timestamp |
---|---|---|---|---|
2006 |
ADD |
2007-04-01 |
3300 |
null |
2007 |
ADD |
2008-04-01 |
35 |
2008-04-02 |
2007 |
MOD |
2008-04-02 |
3500 |
null |
2008 |
ADD |
2009-04-01 |
3700 |
2009-07-01 |
2008 |
MOD |
2009-07-01 |
4100 |
2010-02-01 |
2008 |
MOD |
2010-02-01 |
4000 |
null |
2009 |
ADD |
2010-04-01 |
4500 |
null |
21.27. Determining a suitable partitioning column
To partition this data, the level of relevancy must be defined. Consider the following:
-
For the fiscal year 2006, there is only one revision.
It has the oldest revision timestamp of all audit rows,
but should still be regarded as relevant because it’s the latest modification for this fiscal year in the salary table (its end revision timestamp is null).Also, note that it would be very unfortunate if in 2011 there would be an update of the salary for the fiscal year 2006 (which is possible until at least 10 years after the fiscal year),
and the audit information would have been moved to a slow disk (based on the age of the revision timestamp).
Remember that, in this case, Envers will have to update the end revision timestamp of the most recent audit row. -
There are two revisions in the salary of the fiscal year 2007 which both have nearly the same revision timestamp and a different end revision timestamp.
On first sight, it is evident that the first revision was a mistake and probably not relevant.
The only relevant revision for 2007 is the one with end revision timestamp value of null.
Based on the above, it is evident that only the end revision timestamp is suitable for audit table partitioning.
The revision timestamp is not suitable.
21.28. Determining a suitable partitioning scheme
A possible partitioning scheme for the salary table would be as follows:
- end revision timestamp year = 2008
-
This partition contains audit data that is not very (or no longer) relevant.
- end revision timestamp year = 2009
-
This partition contains audit data that is potentially relevant.
- end revision timestamp year >= 2010 or null
-
This partition contains the most relevant audit data.
This partitioning scheme also covers the potential problem of the update of the end revision timestamp,
which occurs if a row in the audited table is modified.
Even though Envers will update the end revision timestamp of the audit row to the system date at the instant of modification,
the audit row will remain in the same partition (the ‘extension bucket’).
And sometime in 2011, the last partition (or ‘extension bucket’) is split into two new partitions:
-
end revision timestamp year = 2010: This partition contains audit data that is potentially relevant (in 2011).
-
end revision timestamp year >= 2011 or null: This partition contains the most interesting audit data and is the new ‘extension bucket’.
22. Managed Beans
Hibernate supports consuming many of its extension points as «managed beans». A bean being
managed simply means that its creation and lifecycle are managed by a container of some sort.
The main contract for managed beans is org.hibernate.resource.beans.spi.ManagedBeanRegistry
Often these beans are managed by an external service, such as CDI. The contract
org.hibernate.resource.beans.container.spi.BeanContainer
is used to integrate the
external container. ManagedBeanRegistry
integrates support for a BeanContainer
if one is specified.
By default, Hibernate creates references to the beans and links their lifecycle to
the SessionFactory. It supports a number of ways to influence how this process works.
22.1. Manageable Beans
Jakarta Persistence defines support for resolving AttributeConverter
and
«entity listener» classes as managed beans.
Additionally, Hibernate supports resolving the following integrations as managed beans:
-
org.hibernate.type.descriptor.jdbc.JdbcType
-
org.hibernate.type.descriptor.java.BasicJavaType
-
org.hibernate.type.descriptor.java.MutabilityPlan
-
org.hibernate.usertype.UserType
-
org.hibernate.usertype.UserCollectionType
-
org.hibernate.metamodel.EmbeddableInstantiator
-
org.hibernate.envers.RevisionListener
-
org.hibernate.id.IdentifierGenerator
At the moment, when using either delayed or extended CDI access, resolving these Hibernate integrations as managed beans is disabled. |
22.2. CDI BeanContainer
Hibernate provides built-in support for using a CDI BeanManager
as the BeanContainer
.
Jakarta Persistence indicates that the setting jakarta.persistence.bean.manager
be used to pass along a
CDI BeanManager
to use, so Hibernate follows that approach.
22.2.1. CDI BeanManager — default
By default, Hibernate follows the Jakarta Persistence requirements for using
CDI BeanManager
. Most importantly, this means accessing beans from the BeanManager
immediately during bootstrap.
In many cases this can cause circularity problems as CDI is often a consumer of
persistence as well. In such cases, delayed
or extended access should be used
22.2.2. CDI BeanManager — delayed
Rather than accessing the CDI managed beans immediately, Hibernate can be configured
to delay accessing the beans until first needed using hibernate.delay_cdi_access
.
Note however that this has some limitations{fn-cdi-availability}
22.2.3. CDI BeanManager — extended
Sometimes the actual BeanManager
instance is not known until after Hibernate
has been bootstrapped.
For such cases, Hibernate provides the org.hibernate.resource.beans.container.spi.ExtendedBeanManager
contract, which is basically a promise or future for a BeanManager
reference.
An instance of ExtendedBeanManager
passed as jakarta.persistence.bean.manager
triggers this behavior.
The ExtendedBeanManager
implementation accepts the LifecycleListener
passed to its
#registerLifecycleListener
method. It will call LifecycleListener#beanManagerInitialized
and LifecycleListener#beforeBeanManagerDestroyed
as lifecycle callbacks for the real
BeanManager
.
Hibernate uses the LifecycleListener#beanManagerInitialized
callback to get access to the
real BeanManager
.
When used in WildFly, this is all automatically set up by the server |
22.3. Custom BeanContainer
Other containers (Spring, e.g.) can also be used and integrated by implementing BeanContainer
and
declaring it using hibernate.resource.beans.container
.
23. Database Portability Considerations
23.1. Portability Basics
One of the selling points of Hibernate (and really Object/Relational Mapping as a whole) is the notion of database portability.
This could mean an internal IT user migrating from one database vendor to another, or it could mean a framework or deployable application consuming Hibernate to simultaneously target multiple database products by their users.
Regardless of the exact scenario, the basic idea is that you want Hibernate to help you run against any number of databases without changes to your code, and ideally without any changes to the mapping metadata.
23.2. Dialect
The first line of portability for Hibernate is the dialect, which is a specialization of the org.hibernate.dialect.Dialect
contract.
A dialect encapsulates all the differences in how Hibernate must communicate with a particular database to accomplish some task like getting a sequence value or structuring a SELECT query.
Hibernate bundles a wide range of dialects for many of the most popular databases.
If you find that your particular database is not among them, it is not terribly difficult to write your own.
23.3. Dialect resolution
Originally, Hibernate would always require that users specify which dialect to use. In the case of users looking to simultaneously target multiple databases with their build that was problematic.
Generally, this required their users to configure the Hibernate dialect or defining their own method of setting that value.
Starting with version 3.2, Hibernate introduced the notion of automatically detecting the dialect to use based on the java.sql.DatabaseMetaData
obtained from a java.sql.Connection
to that database.
This was much better, except that this resolution was limited to databases Hibernate know about ahead of time and was in no way configurable or overrideable.
Starting with version 3.3, Hibernate has a far more powerful way to automatically determine which dialect to be used by relying on a series of delegates which implement the org.hibernate.dialect.resolver.DialectResolver
which defines only a single method:
public Dialect resolveDialect(DatabaseMetaData metaData) throws JDBCConnectionException
The basic contract here is that if the resolver ‘understands’ the given database metadata then it returns the corresponding Dialect; if not it returns null and the process continues to the next resolver.
The signature also identifies org.hibernate.exception.JDBCConnectionException
as possibly being thrown.
A JDBCConnectionException
here is interpreted to imply a non-transient (aka non-recoverable) connection problem and is used to indicate an immediate stop to resolution attempts.
All other exceptions result in a warning and continuing on to the next resolver.
The cool part about these resolvers is that users can also register their own custom resolvers which will be processed ahead of the built-in Hibernate ones.
This might be useful in a number of different situations:
-
it allows easy integration for auto-detection of dialects beyond those shipped with Hibernate itself.
-
it allows you to specify to use a custom dialect when a particular database is recognized.
To register one or more resolvers, simply specify them (separated by commas, tabs or spaces) using the ‘hibernate.dialect_resolvers’ configuration setting (see the DIALECT_RESOLVERS
constant on org.hibernate.cfg.Environment
).
23.4. Identifier generation
When considering portability between databases, another important decision is selecting the identifier generation strategy you want to use.
Originally, Hibernate provided the native generator for this purpose, which was intended to select between a sequence, identity, or table strategy depending on the capability of the underlying database.
However, an insidious implication of this approach comes about when targeting some databases which support identity generation and some which do not.
identity generation relies on the SQL definition of an IDENTITY (or auto-increment) column to manage the identifier value.
It is what is known as a post-insert generation strategy because the insert must actually happen before we can know the identifier value.
Because Hibernate relies on this identifier value to uniquely reference entities within a persistence context,
it must then issue the insert immediately when the user requests that the entity be associated with the session (e.g. like via save()
or persist()
), regardless of current transactional semantics.
Hibernate was changed slightly, once the implications of this were better understood, so now the insert could be delayed in cases where this is feasible. The underlying issue is that the actual semantics of the application itself changes in these cases. |
Starting with version 3.2.3, Hibernate comes with a set of enhanced identifier generators targeting portability in a much different way.
There are specifically 2 bundled enhanced generators:
|
The idea behind these generators is to port the actual semantics of the identifier value generation to the different databases.
For example, the org.hibernate.id.enhanced.SequenceStyleGenerator
mimics the behavior of a sequence on databases which do not support sequences by using a table.
23.5. Database functions
HQL now provides a large set of functions which are portable between databases.
You can find them listed in the chapter describing the query language.
There’s even a way for a program to contribute its own function definitions.
Of course, SQL functions occurring in handwritten SQL fragments or queries usually aren’t very portable. |
23.6. Type mappings
TODO
23.6.1. BLOB/CLOB mappings
TODO
23.6.2. Boolean mappings
23.6.3. Jakarta Persistence portability
-
HQL/JPQL differences
-
naming strategies
-
basic types
-
simple id types
-
generated id types
-
composite ids and many-to-one
-
«embedded composite identifiers»
24. Statistics
Hibernate can gather all sorts of statistics which can help you get a better insight into what Hibernate does behind the scenes.
By default, the statistics are not collected because this incurs an additional processing and memory overhead. To instruct Hibernate to start collecting statistics, you need to set the hibernate.generate_statistics
configuration property to true
:
<property
name="hibernate.generate_statistics"
value="true"
/>
24.1. org.hibernate.stat.Statistics methods
The Hibernate statistics are made available via the
Statistics
interface which exposes the following methods:
24.1.1. General statistics methods
isStatisticsEnabled
-
Are statistics enabled?
setStatisticsEnabled(boolean b)
-
Enable statistics based on the provided parameter.
clear
-
Reset all statistics.
logSummary
-
Print a summary of the current statistics into the application log.
getStartTime
-
The milliseconds (JVM standard
currentTimeMillis()
) since the initial creation of this Statistics instance or the last timeclear()
was called.
24.1.2. Aggregated statistics methods
getQueries
-
Get executed query strings. The maximum number of queries tracked by the Hibernate statistics is given by the
hibernate.statistics.query_max_size
property. getEntityStatistics(String entityName)
-
Find entity statistics for the given name.
getCollectionStatistics(String role)
-
Get collection statistics per role (collection name).
getNaturalIdStatistics(String entityName)
-
Get the Hibernate-specific natural id resolution statistics for the given entity.
getQueryStatistics(String queryString)
-
Get the statistics for the given query string (JPQL/HQL or native SQL).
getDomainDataRegionStatistics(String regionName)
-
Get the second-level cache statistics per domain data (entity, collection, natural-id) region.
getQueryRegionStatistics(String regionName)
-
Get the second-level cache statistics per query region.
getCacheRegionStatistics(String regionName)
-
Get statistics for either a domain-data or query-result region
(this method checks both, preferring domain data region if one exists).
24.1.3. SessionFactory statistics methods
getEntityNames
-
Get the names of all entities configured with the current
SessionFactory
. getCollectionRoleNames
-
Get the names of all collection roles configured with the current
SessionFactory
.
24.1.4. Session statistics methods
getSessionCloseCount
-
Global number of sessions that got closed.
getSessionOpenCount
-
Global number of sessions that got opened.
getFlushCount
-
Get the global number of flush operations executed (either manual or automatic).
24.1.5. JDBC statistics methods
getPrepareStatementCount
-
The number of JDBC prepared statements that were acquired by Hibernate.
getCloseStatementCount
-
The number of JDBC prepared statements that were released by Hibernate.
getConnectCount
-
Get the global number of connections acquired by the Hibernate sessions (the actual number of connections used may be much smaller depending whether you use a connection pool or not).
24.1.6. Transaction statistics methods
getSuccessfulTransactionCount
-
The number of transactions that completed successfully.
getTransactionCount
-
The number of transactions we know to have completed.
24.1.7. Concurrency Control statistics methods
getOptimisticFailureCount
-
The number of Hibernate
StaleObjectStateException
s or Jakarta PersistenceOptimisticEntityLockException
s that occurred.
24.1.8. Entity statistics methods
getEntityDeleteCount
-
Get the global number of entity deletes.
getEntityInsertCount
-
Get the global number of entity inserts.
getEntityLoadCount
-
Get the global number of entity loads.
getEntityFetchCount
-
Get the global number of entity fetches.
getEntityUpdateCount
-
Get the global number of entity updates.
24.1.9. Collection statistics methods
getCollectionLoadCount
-
Global number of collections that were loaded.
getCollectionFetchCount
-
Global number of collections that were fetched.
getCollectionUpdateCount
-
Global number of collections that were updated.
getCollectionRemoveCount
-
Global number of collections that were removed.
getCollectionRecreateCount
-
Global number of collections that were recreated.
24.1.10. Query statistics methods
getQueryExecutionCount
-
Get the global number of executed queries.
getQueryExecutionMaxTime
-
Get the time in milliseconds of the slowest query.
getQueryExecutionMaxTimeQueryString
-
Get the query string for the slowest query.
getQueryPlanCacheHitCount
-
Get the global number of query plans successfully retrieved from cache.
getQueryPlanCacheMissCount
-
Get the global number of query plans lookups not found in cache.
24.1.11. Natural id statistics methods
getNaturalIdQueryExecutionCount
-
Get the global number of natural id queries executed against the database.
getNaturalIdQueryExecutionMaxTime
-
Get the global maximum query time for natural id queries executed against the database.
getNaturalIdQueryExecutionMaxTimeRegion
-
Get the region for the maximum natural id query time.
getNaturalIdQueryExecutionMaxTimeEntity
-
Get the entity for the maximum natural id query time.
24.1.12. Second-level cache statistics methods
getSecondLevelCacheRegionNames
-
Get all second-level domain data cache region names.
getSecondLevelCacheHitCount
-
Global number of cacheable entities/collections successfully retrieved from the cache.
getSecondLevelCacheMissCount
-
Global number of cacheable entities/collections not found in the cache and loaded from the database.
getSecondLevelCachePutCount
-
Global number of cacheable entities/collections put in the cache.
Second-level cache natural id statistics methods
getNaturalIdCacheHitCount
-
Get the global number of cached natural id lookups successfully retrieved from cache.
getNaturalIdCacheMissCount
-
Get the global number of cached natural id lookups not found in cache.
getNaturalIdCachePutCount
-
Get the global number of cacheable natural id lookups put in cache.
Second-level cache query statistics methods
getQueryCacheHitCount
-
Get the global number of cached queries successfully retrieved from cache.
getQueryCacheMissCount
-
Get the global number of cached queries not found in cache.
getQueryCachePutCount
-
Get the global number of cacheable queries put in cache.
Second-level cache timestamp statistics methods
getUpdateTimestampsCacheHitCount
-
Get the global number of timestamps successfully retrieved from cache.
getUpdateTimestampsCacheMissCount
-
Get the global number of timestamp requests that were not found in the cache.
getUpdateTimestampsCachePutCount
-
Get the global number of timestamps put in cache.
24.2. Query statistics max size
Traditionally, Hibernate stored all executed queries when statistics were enabled. However, this was a very bad default since, if your application runs millions of different queries,
you’d risk running out of memory.
Therefore, to restrict the number of queries the Hibernate statistics can hold, the hibernate.statistics.query_max_size
property was added.
By default, the maximum number of queries retained is 5000, but you can increase this value via the hibernate.statistics.query_max_size
property.
So, if your application makes heavy use of the Jakarta Persistence Criteria API or if you simply have a very large number of queries, you might want to
raise the maximum number of queries that are being stored by the Statistics
instance.
If the maximum number of queries has been reached, Hibernate uses a Least recently used (LRU) policy
to make room for new query entries.
24.3. Query plan cache statistics
Every entity query, be it JPQL/HQL or Criteria API, is compiled to an AST (Abstract Syntax Tree),
and this process is resource-intensive.
To speed up the entity query executions, Hibernate offers a query plan cache so that compiled plans can be reused.
To monitor the query plan cache you have the following statistics.
24.3.1. Query plan cache global statistics
The Statistics
instance provides two global counters which can give you an overall picture of the query plan cache effectiveness.
-
getQueryPlanCacheHitCount
-
getQueryPlanCacheMissCount
If the hit count is high and the miss count is low, then the query plan cache is effective, and the vast majority of entity queries
are served from the query plan cache, rather than being compiled over and over again.
24.3.2. Query plan cache query-level statistics
The QueryStatistics
instance, which you can get via the getQueryStatistics(String queryString)
method of the Statistics
object, stores the following query plan cache metrics:
getPlanCacheHitCount
-
The number of query plans successfully fetched from the cache.
getQueryPlanCacheMissCount
-
The number of query plans not fetched from the cache.
getPlanCompilationTotalMicroseconds
-
The overall time spent to compile the plan for this particular query.
Hibernate provides build-time services available as plugins for
-
Gradle
-
Maven
-
Ant
These services include
-
Bytecode enhancement
-
Static Metamodel generation
-
Schema management
25.1. Bytecode Enhancement
Hibernate performs bytecode enhancement through its org.hibernate.bytecode.enhance.spi.Enhancer
contract. These build time tools provide a way to incorporate configuration and execution of
the enhancer into a build.
See Bytecode Enhancement for discussion of the capabilities of an enhanced model.
At the moment, only annotated classes are supported for enhancement. |
25.1.1. Runtime Bytecode Enhancement
Hibernate can also perform run-time bytecode enhancement when used in Jakarta EE compliant
containers through jakarta.persistence.spi.ClassTransformer
. See the documentation of
your container for any additional details. Run-time enhancement is controlled through
3 true/false settings (all of which default to false):
hibernate.enhancer.enableDirtyTracking
-
Whether to enhance the model for dirty-tracking. This setting is deprecated for removal without a replacement.
hibernate.enhancer.enableLazyInitialization
-
Whether to enhance the model for lazy loading at the attribute level. This allows
even basic types to be fetched lazily. It also allows definition of fetch groups (LazyGroup
). This setting is deprecated for removal without a replacement. hibernate.enhancer.enableAssociationManagement
-
Whether to automatically synchronize a bidirectional association when only one side is changed.
25.2. Static Metamodel Generator
Jakarta Persistence defines a typesafe Criteria API which allows Criteria
queries to be constructed in a
strongly-typed manner, utilizing so-called static metamodel classes. For developers, it is important that
the task of the metamodel generation can be automated. Hibernate Static Metamodel Generator is an annotation
processor based on JSR_269 with the task of creating Jakarta Persistence
static metamodel classes.
See Criteria for discussion of Jakarta Persistence criteria queries.
The Hibernate Static Metamodel Generator is defined by the published org.hibernate.orm:metamodel-generator
artifact. As it is defined as an
annotation processor,
it is usable anytime javac
is used. See the tool-specific discussions (Gradle, Maven
and Ant) for details on integrating the generator into those environments.
- NOTE
-
The fully qualified name of the processor class is
org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor
.
The Run |
The structure of the metamodel classes is described in the Jakarta Persistence
specification, but for completeness the definition is repeated in the following
paragraphs. For every class in a persistence-unit, the generator will produce
a static metamodel class based on the following rules:
-
For each managed class
X
in packagep
, a metamodel classX_
is created in packagep
. -
The name of the metamodel class is derived from the name of the managed class by appending «_» to the managed class name.
-
The metamodel class
X_
must be annotated with thejakarta.persistence.StaticMetamodel
annotation. The generation
can also be configured to add thejavax.annotation.processing.Generated
annotation. -
If class
X
extends another classS
, whereS
is the most derived managed class extended byX
, then
classX_
must extend classS_
, whereS_
is the metamodel class created forS
. -
For every persistent singular attribute
y
declared by classX
, where the type ofy
isY
,
the metamodel class must contain a declaration as follows:public static volatile SingularAttribute<X, Y> y;
-
For every persistent plural attribute
z
declared by classX
, where the element type ofz
isZ
, the metamodel
class must contain a declaration as follows:-
if the collection type of
z
isjava.util.Collection
, thenpublic static volatile CollectionAttribute<X, Z> z;
-
if the collection type of
z
isjava.util.Set
, thenpublic static volatile SetAttribute<X, Z> z;
-
if the collection type of
z
isjava.util.List
, thenpublic static volatile ListAttribute<X, Z> z;
-
if the collection type of
z
isjava.util.Map
, thenpublic static volatile MapAttribute<X, K, Z> z;
where
K
is the type of the key of the map in classX
-
-
Import statements must be included for
jakarta.persistence.metamodel
types as
needed, as well as all domain model classes (i.e.,X
,S
,Y
,Z
, andK
).
As an example, consider the following domain model —
Given this model, the generator will produce classes named Customer_
, Order_
and Item_
. As an example:
At boot-time, Hibernate will find these classes and populate them. They can then be used in
Criteria queries for type-safe path references. For example:
25.3. Schema Management
Coming soon
25.4. Gradle Plugin
For integrating with Gradle, Hibernate provides the
org.hibernate.orm plugin which
supports bytecode enhancement and static metamodel generation but not schema tooling.
To apply the plugin, use Gradle’s plugins {}
block:
plugins {
id "org.hibernate.orm" version "<version-to-use>"
}
Applying the plugin creates a hibernate
extension (HibernateOrmSpec
) to configure the plugin.
By default, when the plugin is applied, support for both bytecode enhancement and static metamodel
generation is enabled.
hibernate {
// for illustration, let's disable both
disableEnhancement
disableJpaMetamodel
}
25.4.1. Bytecode Enhancement
Enhancement is configured through the enhancement
extension:
hibernate {
enhancement {
// for illustration, enable them all
lazyInitialization true
dirtyTracking true
associationManagement true
}
}
The extension is of type EnhancementSpec
which exposes the following properties:
- enableLazyInitialization
-
Whether to incorporate lazy loading support into the enhanced bytecode. Defaults to
true
. This setting is deprecated for removal without a replacement. - enableDirtyTracking
-
Whether to incorporate dirty tracking into the enhanced bytecode. Defaults to
true
. This setting is deprecated for removal without a replacement. - enableAssociationManagement
-
Whether to add bidirectional association management into the enhanced bytecode
Which all default to false (disabled).
It also exposes the following method forms:
-
lazyInitialization(boolean)
-
dirtyTracking(boolean)
-
associationManagement(boolean)
25.4.2. Static Metamodel Generation
One approach to integrate Static Metamodel generation into a Gradle build is to
use Gradle’s support for annotation processors —
dependencies {
annotationProcessor "org.hibernate.orm:hibernate-jpamodelgen:${hibernateVersion}"
}
When the build does not need bytecode enhancement support, this is a perfectly valid solution.
The plugin supports simpler configuration of the generator using the registered
jpaMetamodel
extension:
hibernate {
jpaMetamodel {
applyGeneratedAnnotation false
suppress 'raw'
generationOutputDirectory "${buildDir}/generated/sources/modelgen"
compileOutputDirectory "${buildDir}/classes/java/modelgen"
}
}
The extension is of type JpaMetamodelGenerationSpec
, which exposes the following configuration properties:
- applyGeneratedAnnotation
-
Should the
javax.annotation.processing.Generated
annotation be added to the
generated classes. Defaults totrue
. - suppressions
-
Suppressions to add to the generated classes. Defaults to
['raw', 'deprecation']
- generationOutputDirectory
-
Directory where the generated metamodel classes should be created. Defaults
to${buildDir}/generated/sources/jpaMetamodel
It also exposes the following method forms:
-
applyGeneratedAnnotation(boolean)
-
suppress(String)
-
generationOutputDirectory(Object)
-
compileOutputDirectory(Object)
25.5. Maven Plugin
Hibernate provides a Maven plugin capable of providing
build-time enhancement of the domain model as they are compiled as part of a Maven
build. See the section on the Gradle Plugin for details
on the configuration settings. By default, all enhancements are disabled.
Example 691. Apply the Maven plugin
<build>
<plugins>
[...]
<plugin>
<groupId>org.hibernate.orm.tooling</groupId>
<artifactId>hibernate-enhance-maven-plugin</artifactId>
<version>$currentHibernateVersion</version>
<executions>
<execution>
<configuration>
<failOnError>true</failOnError>
<enableLazyInitialization>true</enableLazyInitialization>
<enableDirtyTracking>true</enableDirtyTracking>
<enableAssociationManagement>true</enableAssociationManagement>
</configuration>
<goals>
<goal>enhance</goal>
</goals>
</execution>
</executions>
</plugin>
[...]
</plugins>
</build>
25.6. Ant Plugin
Hibernate provides Ant support …
25.6.1. Static Metamodel Generation in Ant
As mentioned in Static Metamodel Generator, the generator is implemented as an
annotation processor and can be used anywhere javac is used — such as
Ant’s javac task.
Example 692. Javac task configuration
<javac srcdir="${src.dir}"
destdir="${target.dir}"
failonerror="false"
fork="true"
classpath="${classpath}">
<compilerarg value="-processorpath" />
<compilerarg value="/path/to/metamodel-generator.jar"/>
<compilerarg value="-proc:only"/>
</javac>
25.6.2. Schema Management
Coming soon
26. Performance Tuning and Best Practices
Every enterprise system is unique. However, having a very efficient data access layer is a common requirement for many enterprise applications.
Hibernate comes with a great variety of features that can help you tune the data access layer.
26.1. Schema management
Although Hibernate provides the update
option for the hibernate.hbm2ddl.auto
configuration property,
this feature is not suitable for a production environment.
An automated schema migration tool (e.g. Flyway, Liquibase) allows you to use any database-specific DDL feature (e.g. Rules, Triggers, Partitioned Tables).
Every migration should have an associated script, which is stored on the Version Control System, along with the application source code.
When the application is deployed on a production-like QA environment, and the deployment worked as expected, then pushing the deployment to a production environment should be straightforward since the latest schema migration was already tested.
You should always use an automatic schema migration tool and have all the migration scripts stored in the Version Control System. |
26.2. Logging
Whenever you’re using a framework that generates SQL statements on your behalf, you have to ensure that the generated statements are the ones that you intended in the first place.
There are several alternatives to logging statements.
You can log statements by configuring the underlying logging framework.
For Log4j, you can use the following appenders:
### log just the SQL
log4j.logger.org.hibernate.SQL=debug
### log JDBC bind parameters and extracted values ###
log4j.logger.org.hibernate.type=trace
log4j.logger.org.hibernate.orm.jdbc.bind=trace
log4j.logger.org.hibernate.orm.jdbc.extract=trace
However, there are some other alternatives like using datasource-proxy or p6spy.
The advantage of using a JDBC Driver
or DataSource
proxy is that you can go beyond simple SQL logging:
-
statement execution time
-
JDBC batching logging
-
database connection monitoring
Another advantage of using a DataSource
proxy is that you can assert the number of executed statements at test time.
This way, you can have the integration tests fail when a N+1 query issue is automatically detected.
26.3. JDBC batching
JDBC allows us to batch multiple SQL statements and to send them to the database server into a single request.
This saves database roundtrips, and so it reduces response time significantly.
Not only INSERT
and UPDATE
statements, but even DELETE
statements can be batched as well.
For INSERT
and UPDATE
statements, make sure that you have all the right configuration properties in place, like ordering inserts and updates and activating batching for versioned data.
Check out this article for more details on this topic.
For DELETE
statements, there is no option to order parent and child statements, so cascading can interfere with the JDBC batching process.
Unlike any other framework which doesn’t automate SQL statement generation, Hibernate makes it very easy to activate JDBC-level batching as indicated in the Batching chapter.
26.4. Mapping
Choosing the right mappings is very important for a high-performance data access layer.
From the identifier generators to associations, there are many options to choose from, yet not all choices are equal from a performance perspective.
26.4.1. Identifiers
When it comes to identifiers, you can either choose a natural id or a synthetic key.
For natural identifiers, the assigned identifier generator is the right choice.
For synthetic keys, the application developer can either choose a randomly generated fixed-size sequence (e.g. UUID) or a natural identifier.
Natural identifiers are very practical, being more compact than their UUID counterparts, so there are multiple generators to choose from:
-
IDENTITY
-
SEQUENCE
-
TABLE
Although the TABLE
generator addresses the portability concern, in reality, it performs poorly because it requires emulating a database sequence using a separate transaction and row-level locks.
For this reason, the choice is usually between IDENTITY
and SEQUENCE
.
If the underlying database supports sequences, you should always use them for your Hibernate entity identifiers. Only if the relational database does not support sequences (e.g. MySQL 5.7), you should use the |
If you’re using the SEQUENCE
generator, then you should be using the enhanced identifier generators that were enabled by default in Hibernate 5.
The pooled and the pooled-lo optimizers are very useful to reduce the number of database roundtrips when writing multiple entities per database transaction.
26.4.2. Associations
Jakarta Persistence offers four entity association types:
-
@ManyToOne
-
@OneToOne
-
@OneToMany
-
@ManyToMany
And an @ElementCollection
for collections of embeddables.
Because object associations can be bidirectional, there are many possible combinations of associations.
However, not every possible association type is efficient from a database perspective.
The closer the association mapping is to the underlying database relationship, the better it will perform. On the other hand, the more exotic the association mapping, the better the chance of being inefficient. |
Therefore, the @ManyToOne
and the @OneToOne
child-side association are best to represent a FOREIGN KEY
relationship.
The parent-side @OneToOne
association requires bytecode enhancement
so that the association can be loaded lazily. Otherwise, the parent-side association is always fetched even if the association is marked with FetchType.LAZY
.
For this reason, it’s best to map @OneToOne
association using @MapsId
so that the PRIMARY KEY
is shared between the child and the parent entities.
When using @MapsId
, the parent-side association becomes redundant since the child-entity can be easily fetched using the parent entity identifier.
For collections, the association can be either:
-
unidirectional
-
bidirectional
For unidirectional collections, Set
s are the best choice because they generate the most efficient SQL statements.
Unidirectional List
s are less efficient than a @ManyToOne
association.
Bidirectional associations are usually a better choice because the @ManyToOne
side controls the association.
Embeddable collections (@ElementCollection
) are unidirectional associations, hence Set
s are the most efficient, followed by ordered List
s, whereas bags (unordered List
s) are the least efficient.
The @ManyToMany
annotation is rarely a good choice because it treats both sides as unidirectional associations.
For this reason, it’s much better to map the link table as depicted in the Bidirectional many-to-many with link entity lifecycle section.
Each FOREIGN KEY
column will be mapped as a @ManyToOne
association.
On each parent-side, a bidirectional @OneToMany
association is going to map to the aforementioned @ManyToOne
relationship in the link entity.
Just because you have support for collections, it does not mean that you have to turn any one-to-many database relationship into a collection. Sometimes, a |
26.5. Inheritance
Jakarta Persistence offers SINGLE_TABLE
, JOINED
, and TABLE_PER_CLASS
to deal with inheritance mapping, and each of these strategies has advantages and disadvantages.
-
SINGLE_TABLE
performs the best in terms of executed SQL statements. However, you cannot useNOT NULL
constraints on the column-level. You can still use triggers and rules to enforce such constraints, but it’s not as straightforward. -
JOINED
addresses the data integrity concerns because every subclass is associated with a different table.
Polymorphic queries or@OneToMany
base class associations don’t perform very well with this strategy.
However, polymorphic@ManyToOne
associations are fine, and they can provide a lot of value. -
TABLE_PER_CLASS
should be avoided since it does not render efficient SQL statements.
26.6. Fetching
Fetching too much data is the number one performance issue for the vast majority of Jakarta Persistence applications. |
Hibernate supports both entity queries (JPQL/HQL and Criteria API) and native SQL statements.
Entity queries are useful only if you need to modify the fetched entities, therefore benefiting from the automatic dirty checking mechanism.
For read-only transactions, you should fetch DTO projections because they allow you to select just as many columns as you need to fulfill a certain business use case.
This has many benefits like reducing the load on the currently running Persistence Context because DTO projections don’t need to be managed.
26.6.1. Fetching associations
Related to associations, there are two major fetch strategies:
-
EAGER
-
LAZY
EAGER
fetching is almost always a bad choice.
Prior to Jakarta Persistence, Hibernate used to have all associations as The |
So, EAGER
fetching is to be avoided. For this reason, it’s better if all associations are marked as LAZY
by default.
However, LAZY
associations must be initialized prior to being accessed. Otherwise, a LazyInitializationException
is thrown.
There are good and bad ways to treat the LazyInitializationException
.
The best way to deal with LazyInitializationException
is to fetch all the required associations prior to closing the Persistence Context.
The JOIN FETCH
directive is good for @ManyToOne
and OneToOne
associations, and for at most one collection (e.g. @OneToMany
or @ManyToMany
).
If you need to fetch multiple collections, to avoid a Cartesian Product, you should use secondary queries which are triggered either by navigating the LAZY
association or by calling Hibernate#initialize(Object proxy)
method.
26.7. Caching
Hibernate has two caching layers:
-
the first-level cache (Persistence Context) which provides application-level repeatable reads.
-
the second-level cache which, unlike application-level caches, doesn’t store entity aggregates but normalized dehydrated entity entries.
The first-level cache is not a caching solution «per se», being more useful for ensuring READ COMMITTED
isolation level.
While the first-level cache is short-lived, being cleared when the underlying EntityManager
is closed, the second-level cache is tied to an EntityManagerFactory
.
Some second-level caching providers offer support for clusters. Therefore, a node needs only to store a subset of the whole cached data.
Although the second-level cache can reduce transaction response time since entities are retrieved from the cache rather than from the database,
there are other options to achieve the same goal,
and you should consider these alternatives prior to jumping to a second-level cache layer:
-
tuning the underlying database cache so that the working set fits into memory, therefore reducing Disk I/O traffic.
-
optimizing database statements through JDBC batching, statement caching, indexing can reduce the average response time, therefore increasing throughput as well.
-
database replication is also a very valuable option to increase read-only transaction throughput.
After properly tuning the database, to further reduce the average response time and increase the system throughput, application-level caching becomes inevitable.
Typically, a key-value application-level cache like Memcached or Redis is a common choice to store data aggregates.
If you can duplicate all data in the key-value store, you have the option of taking down the database system for maintenance without completely losing availability since read-only traffic can still be served from the cache.
One of the main challenges of using an application-level cache is ensuring data consistency across entity aggregates.
That’s where the second-level cache comes to the rescue.
Being tightly integrated with Hibernate, the second-level cache can provide better data consistency since entries are cached in a normalized fashion, just like in a relational database.
Changing a parent entity only requires a single entry cache update, as opposed to cache entry invalidation cascading in key-value stores.
The second-level cache provides four cache concurrency strategies:
-
READ_ONLY
-
NONSTRICT_READ_WRITE
-
READ_WRITE
-
TRANSACTIONAL
READ_WRITE
is a very good default concurrency strategy since it provides strong consistency guarantees without compromising throughput.
The TRANSACTIONAL
concurrency strategy uses JTA. Hence, it’s more suitable when entities are frequently modified.
Both READ_WRITE
and TRANSACTIONAL
use write-through caching, while NONSTRICT_READ_WRITE
is a read-through caching strategy.
For this reason, NONSTRICT_READ_WRITE
is not very suitable if entities are changed frequently.
When using clustering, the second-level cache entries are spread across multiple nodes.
When using Infinispan distributed cache, only READ_WRITE
and NONSTRICT_READ_WRITE
are available for read-write caches.
Bear in mind that NONSTRICT_READ_WRITE
offers a weaker consistency guarantee since stale updates are possible.
27. Credits
The full list of contributors to Hibernate ORM can be found on the
GitHub repository.
The following contributors were involved in this documentation:
-
Gail Badner
-
Christian Bauer
-
Christian Beikov
-
Marco Belladelli
-
Emmanuel Bernard
-
Andrea Boriero
-
Chris Cranford
-
Steve Ebersole
-
Hardy Ferentschik
-
Sanne Grinovero
-
Louis Jacomet
-
Gavin King
-
Karel Maesen
-
Brett Meyer
-
Vlad Mihalcea
-
Gunnar Morling
-
Yoann Rodière
-
Max Rydahl Andersen
-
Jan Schatteman
-
Fábio Ueno
-
Radim Vansa
-
Nathan Xu
Appendix A: Configuration Settings
Configuration settings can be broadly broken down into 3 categories —
- Jakarta Persistence
-
Settings which are standardized by the Jakarta Persistence specification for configuring any persistence provider. These
settings are defined by thejakarta.persistence.
namespace - Hibernate
-
Hibernate-specific settings which control various Hibernate behaviors which are extensions to or outside the scope
of the Jakarta Persistence specification. These settings are defined by thehibernate.
namespace - Legacy JPA
-
Settings which were standardized by Java Persistence, the legacy version of the Jakarta Persistence specification
(prior to version 3.1). These settings are defined by thejavax.persistence.
namespace
For the time being, Hibernate continues to support the legacy Java Persistence settings in addition to For (legacy) Hibernate settings which have a direct Jakarta Persistence corollary, the Jakarta Persistence |
A.1. Jakarta Persistence Compliance Settings
hibernate.jpa.compliance
-
Specifies a default value for all
JpaCompliance
flags. Each individual flag may still be overridden by explicitly specifying its specific configuration property.
hibernate.jpa.compliance.caching
-
By default, Hibernate uses second-level cache invalidation for entities with secondary tables in order to avoid the possibility of inconsistent cached data in the case where different transactions simultaneously update different table rows corresponding to the same entity instance.
The Jakarta Persistence TCK, requires that entities with secondary tables be immediately cached in the second-level cache rather than invalidated and re-cached on a subsequent read.
hibernate.jpa.compliance.closed
hibernate.jpa.compliance.global_id_generators
-
Determines whether the scope of any identifier generator name specified via
TableGenerator.name()
orSequenceGenerator.name()
is considered global to the persistence unit, or local to the entity in which identifier generator is defined.
hibernate.jpa.compliance.list
-
Controls whether Hibernate should treat what it would usually consider a «bag», that is, a list with no index column, whose element order is not persistent, as a true
list
with an index column and a persistent element order.
hibernate.jpa.compliance.load_by_id
hibernate.jpa.compliance.orderby
-
JPA specifies that items occurring in
OrderBy
lists must be references to entity attributes, whereas Hibernate, by default, allows more complex expressions.
hibernate.jpa.compliance.proxy
-
The JPA specification insists that an
EntityNotFoundException
must be thrown whenever an uninitialized entity proxy with no corresponding row in the database is accessed. For most programs, this results in many completely unnecessary round trips to the database.Traditionally, Hibernate does not initialize an entity proxy when its identifier attribute is accessed, since the identifier value is already known and held in the proxy instance. This behavior saves the round trip to the database.
hibernate.jpa.compliance.query
-
Controls whether Hibernate’s handling of
Query
(JPQL, Criteria and native) should strictly follow the requirements defined in the Jakarta Persistence specification, both in terms of JPQL validation and behavior ofQuery
method implementations.
hibernate.jpa.compliance.transaction
-
When enabled, specifies that the Hibernate
Transaction
should behave according to the semantics defined by the JPA specification for anEntityTransaction
.
A.2. Persistence Unit Settings
jakarta.persistence.provider
-
Specifies a class implementing
PersistenceProvider
. Naturally, this should always beHibernatePersistenceProvider
, which is the best damn persistence provider ever. There’s no need to explicitly specify this setting when there are no inferior persistence providers floating about.See JPA 2 sections 9.4.3 and 8.2.1.4
jakarta.persistence.transactionType
-
Specifies the type of transactions supported by the entity managers. The default depends on whether the program is considered to be executing in a Java SE or EE environment:
-
For Java SE, the default is
RESOURCE_LOCAL
. -
For Java EE, the default is
JTA
.
See JPA 2 sections 9.4.3 and 8.2.1.2
-
hibernate.archive.autodetection
-
Identifies a comma-separated list of values indicating the types of things we should auto-detect during scanning. Allowable values include:
-
"class"
specifies that.class
files are discovered as managed classes -
"hbm"
specifies thathbm.xml
files are discovered as mapping files
-
hibernate.archive.interpreter
-
Specifies an
ArchiveDescriptorFactory
to use in the scanning process, either:-
an instance of
ArchiveDescriptorFactory
, -
a
Class
representing a class that implementsArchiveDescriptorFactory
, or -
the name of a class that implements
ArchiveDescriptorFactory
.
See information on
Scanner
about expected constructor forms. -
hibernate.archive.scanner
-
Specifies an implementation of
Scanner
, either:-
an instance of
Scanner
, -
a
Class
representing a class that implementsScanner
-
the name of a class that implements
Scanner
.
-
hibernate.jpa_callbacks.enabled
-
Allows JPA callbacks (via
PreUpdate
and friends) to be completely disabled. Mostly useful to save some memory when they are not used.JPA callbacks are enabled by default. Set this property to
false
to disable them.Experimental and will likely be removed as soon as the memory overhead is resolved.
hibernate.persistenceUnitName
-
Specifies the name of the persistence unit.
hibernate.session_factory_name
-
Setting used to name the Hibernate
SessionFactory
.Naming the SessionFactory allows for it to be properly serialized across JVMs as long as the same name is used on each JVM.
If
SESSION_FACTORY_NAME_IS_JNDI
is set totrue
, this is also the name under which the SessionFactory is bound into JNDI on startup and from which it can be obtained from JNDI.
hibernate.session_factory_name_is_jndi
-
Does the value defined by
SESSION_FACTORY_NAME
represent a JNDI namespace into which theSessionFactory
should be bound and made accessible?Defaults to
true
for backwards compatibility.Set this to
false
if naming a SessionFactory is needed for serialization purposes, but no writable JNDI context exists in the runtime environment or if the user simply does not want JNDI to be used.
hibernate.session_factory_observer
-
Specifies a class which implements
SessionFactoryObserver
and has a constructor with no parameters.
javax.persistence.transactionType
-
The type of transactions supported by the entity managers.
See JPA 2 sections 9.4.3 and 8.2.1.2
A.3. JDBC Settings
jakarta.persistence.jdbc.driver
-
Specifies the name of a JDBC driver to use to connect to the database.
See section 8.2.1.9
jakarta.persistence.jdbc.password
-
Specifies the password to use when connecting via JDBC.
See JPA 2 section 8.2.1.9
jakarta.persistence.jdbc.url
-
Specifies the JDBC connection URL to use to connect to the database.
See section 8.2.1.9
hibernate.connection
-
A prefix for properties specifying arbitrary JDBC connection properties. These properties are simply passed along to the provider when creating a connection.
For example, declaring
hibernate.connection.foo=bar
tells Hibernate to appendfoo=bar
to the JDBC connection URL.
hibernate.connection.handling_mode
-
Specifies how Hibernate should manage JDBC connections in terms of acquisition and release, either:
-
an instance of the enumeration
PhysicalConnectionHandlingMode
, or -
the name of one of its instances.
The default is
DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION
. -
hibernate.connection.isolation
-
Specified the JDBC transaction isolation level.
hibernate.connection.pool_size
-
Specifies the maximum number of inactive connections for the built-in connection pool.
hibernate.connection.provider_class
-
Specifies a
ConnectionProvider
to use for obtaining JDBC connections, either:-
an instance of
ConnectionProvider
, -
a
Class
representing a class that implementsConnectionProvider
, or -
the name of a class that implements
ConnectionProvider
.
The term
"class"
appears in the setting name due to legacy reasons; however it can accept instances. -
hibernate.connection.provider_disables_autocommit
-
Indicates that Connections obtained from the configured
ConnectionProvider
have auto-commit already disabled when they are acquired.It is inappropriate to set this value to
true
when the Connections returned by the provider do not, in fact, have auto-commit disabled. Doing so may lead to Hibernate executing SQL operations outside the scope of any transaction.
hibernate.dialect
-
-
an instance of
Dialect
, -
a
Class
representing a class that extendsDialect
, or -
the name of a class that extends
Dialect
.
By default, Hibernate will attempt to automatically determine the dialect from the JDBC URL and JDBC metadata, so this setting is not usually necessary.
-
hibernate.dialect.native_param_markers
-
Controls whether to use JDBC markers (
?
) or dialect native markers for parameters within preparable SQL statements.
hibernate.format_sql
-
Enables formatting of SQL logged to the console.
hibernate.highlight_sql
-
Enables highlighting of SQL logged to the console using ANSI escape codes.
hibernate.jdbc.fetch_size
-
Gives the JDBC driver a hint as to the number of rows that should be fetched from the database when more rows are needed. If
0
, the JDBC driver’s default settings will be used.
hibernate.jdbc.lob.non_contextual_creation
-
When enabled, specifies that Hibernate should not use contextual LOB creation.
hibernate.jdbc.log.warnings
-
When enabled, specifies that JDBC statement warnings should be logged.
hibernate.jdbc.time_zone
-
Specifies the time zone to use in the JDBC driver, which is supposed to match the database timezone.
The time zone may be given as:
-
an instance of
TimeZone
, -
an instance of
ZoneId
, or -
a time zone ID string to be passed to
ZoneId.of(String)
.
-
hibernate.jdbc.use_get_generated_keys
-
Specifies that generated primary keys may be retrieved using the JDBC 3
Statement.getGeneratedKeys()
operation.Usually, performance will be improved if this behavior is enabled, assuming the JDBC driver supports
getGeneratedKeys()
.
hibernate.log_slow_query
-
Specifies a duration in milliseconds defining the minimum query execution time that characterizes a «slow» query. Any SQL query which takes longer than this amount of time to execute will be logged.
A value of
0
, the default, disables logging of «slow» queries.
hibernate.session_factory.statement_inspector
-
-
an instance of
StatementInspector
, -
a
Class
representing an class that implementsStatementInspector
, or -
the name of a class that implements
StatementInspector
.
-
hibernate.show_sql
-
Enables logging of generated SQL to the console.
A.4. C3P0 Connection Pool Settings
hibernate.c3p0
-
A setting prefix used to indicate settings that target the hibernate-c3p0 integration
hibernate.c3p0.acquire_increment
-
Number of connections acquired when pool is exhausted
hibernate.c3p0.idle_test_period
-
Idle time before a C3P0 pooled connection is validated
hibernate.c3p0.max_size
-
Maximum size of C3P0 connection pool
hibernate.c3p0.max_statements
-
Maximum size of C3P0 statement cache
hibernate.c3p0.min_size
-
Minimum size of C3P0 connection pool
hibernate.c3p0.timeout
-
Maximum idle time for C3P0 connection pool
A.5. Proxool Connection Pool Settings
hibernate.proxool
-
A setting prefix used to indicate settings that target the hibernate-proxool integration
hibernate.proxool.existing_pool
-
Proxool property to configure the Proxool Provider from an already existing pool (
true
/false
)
hibernate.proxool.properties
-
Proxool property to configure the Proxool provider using a properties file (
/path/to/proxool.properties
)
hibernate.proxool.xml
-
Proxool property to configure the Proxool provider using an XML (
/path/to/file.xml
)
A.6. Domain Mapping Settings
hibernate.auto_quote_keyword
-
Specifies whether to automatically quote any names that are deemed keywords on the underlying database.
hibernate.create_empty_composites.enabled
-
Enable instantiation of composite/embedded objects when all attribute values are
null
. The default (and historical) behavior is that anull
reference will be used to represent the composite value when all of its attributes arenull
.
hibernate.default_catalog
-
A default database catalog name to use for unqualified database object (table, sequence, …) names
hibernate.default_schema
-
A default database schema (owner) name to use for unqualified database object (table, sequence, …) names
hibernate.discriminator.ignore_explicit_for_joined
-
Controls whether Hibernate should ignore explicit discriminator metadata with joined inheritance.
Hibernate does not need a discriminator with joined inheritance. Historically it simply ignored discriminator metadata. When enabled (
true
), any discriminator metadata (DiscriminatorColumn
, e.g.) is ignored allowing for backwards compatibility.
hibernate.discriminator.implicit_for_joined
-
Controls whether Hibernate should infer a discriminator for entity hierarchies defined with joined inheritance.
Hibernate does not need a discriminator with joined inheritance. Therefore, its legacy behavior is to not infer a discriminator. However, some JPA providers do require discriminators with joined inheritance, so in the interest of portability this option has been added to Hibernate. When enabled (
true
), Hibernate will treat the absence of discriminator metadata as an indication to use the JPA defined defaults for discriminators.
hibernate.globally_quoted_identifiers
-
When enabled, all database identifiers are quoted.
Corollary to the JPA
<delimited-identifiers/>
element within theorm.xml
<persistence-unit-defaults/>
element, but offered as a global flag.
hibernate.globally_quoted_identifiers_skip_column_definitions
-
When global quoting is enabled, JPA states that column-definitions are subject to quoting. However, this can lead to problems with definitions such as
@Column(…, columnDefinition="INTEGER DEFAULT 20")
.
hibernate.id.db_structure_naming_strategy
-
An implicit naming strategy for database structures (tables, sequences) related to identifier generators.
The recognized short names being:
-
«single»
-
«legacy»
-
«standard»
-
hibernate.id.generator.stored_last_used
-
Determines if the identifier value stored in the database table backing a table generator is the last value returned by the identifier generator, or the next value to be returned.
hibernate.id.optimizer.pooled.preferred
-
When a generator specifies an increment-size and an optimizer was not explicitly specified, which of the «pooled» optimizers should be preferred? Can specify an optimizer short name or the name of a class which implements
Optimizer
.
hibernate.id.sequence.increment_size_mismatch_strategy
-
This setting defines the
SequenceMismatchStrategy
used when Hibernate detects a mismatch between a sequence configuration in an entity mapping and its database sequence object counterpart.
hibernate.mapping.default_list_semantics
-
Accepts any of:
-
an instance of
CollectionClassification
-
the (case insensitive) name of a
CollectionClassification
(list e.g.) -
a
Class
representing eitherList
orCollection
-
hibernate.mapping.precedence
-
Specifies the order in which metadata sources should be processed, is a delimited list of values defined by
MetadataSourceType
.
hibernate.physical_naming_strategy
hibernate.timezone.default_storage
-
Specifies the default strategy for storage of the timezone information for the zoned datetime types
OffsetDateTime
andZonedDateTime
. The possible options for this setting are enumerated byTimeZoneStorageType
.
hibernate.transform_hbm_xml.enabled
-
Enables processing
hbm.xml
mappings by transforming them tomapping.xml
and using that processor.
hibernate.transform_hbm_xml.unsupported_feature_handling
-
How features in a
hbm.xml
file which are not supported for transformation should be handled. Valid values are defined byUnsupportedFeatureHandling
hibernate.type.json_format_mapper
-
Specifies a
FormatMapper
used for JSON serialization and deserialization, either:-
an instance of
FormatMapper
, -
a
Class
representing a class that implementsFormatMapper
, -
the name of a class that implements
FormatMapper
, or -
one of the shorthand constants
jackson
orjsonb
.
By default, the first of the possible providers that is available at runtime is used, according to the listing order.
-
hibernate.type.preferred_boolean_jdbc_type
-
Specifies the preferred JDBC type for storing boolean values.
Can also specify the name of the
SqlTypes
constant field, for example,hibernate.type.preferred_boolean_jdbc_type=BIT
.
hibernate.type.preferred_duration_jdbc_type
-
The preferred JDBC type to use for storing
Duration
values.Can also specify the name of the
SqlTypes
constant field, for example,hibernate.type.preferred_duration_jdbc_type=INTERVAL_SECOND
.
hibernate.type.preferred_instant_jdbc_type
-
Specifies the preferred JDBC type for storing
Instant
values.Can also specify the name of the
SqlTypes
constant field, for example,hibernate.type.preferred_instant_jdbc_type=TIMESTAMP
.
hibernate.type.preferred_uuid_jdbc_type
-
The preferred JDBC type to use for storing
UUID
values.Can also specify the name of the
SqlTypes
constant field, for example,hibernate.type.preferred_uuid_jdbc_type=CHAR
.
hibernate.type.wrapper_array_handling
-
Configurable control over how to handle
Byte[]
andCharacter[]
types encountered in the application domain model. Allowable semantics are defined byWrapperArrayHandling
. Accepted values include:-
WrapperArrayHandling
instance -
case-insensitive name of a
WrapperArrayHandling
instance (e.g.allow
)
-
hibernate.type.xml_format_mapper
-
Specifies a
FormatMapper
used for XML serialization and deserialization, either:-
an instance of
FormatMapper
, -
a
Class
representing a class that implementsFormatMapper
, -
the name of a class that implements
FormatMapper
, or -
one of the shorthand constants
jackson
orjaxb
.
By default, the first of the possible providers that is available at runtime is used, according to the listing order.
-
hibernate.use_entity_where_clause_for_collections
-
The
@Where
annotation specifies a restriction on the table rows which are visible as entity class instances or collection elements.This setting controls whether the restriction applied to an entity should be applied to association fetches (for one-to-one, many-to-one, one-to-many, and many-to-many associations) which target the entity.
hibernate.use_nationalized_character_data
-
By default, Hibernate maps character data represented by
String
s andClob
s to the JDBC typesTypes.VARCHAR
andTypes.CLOB
. This setting, when enabled, turns on the use of explicit nationalized character support for mappings involving character data, specifying that the JDBC typesTypes.NVARCHAR
andTypes.NCLOB
should be used instead.This setting is relevant for use with databases with explicit nationalization support, and it is not needed for databases whose native
varchar
andclob
types support Unicode data. (If you’re not sure how your database handles Unicode, check out the implementation ofDialect.getNationalizationSupport()
for its SQL dialect.)Enabling this setting has two effects:
-
when interacting with JDBC, Hibernate uses operations like
PreparedStatement.setNString(int, String)
PreparedStatement.setNClob(int, java.sql.NClob)
to pass character data, and -
when generating DDL, the schema export tool uses
nchar
,nvarchar
, ornclob
as the generated column type when no column type is explicitly specified usingColumn.columnDefinition()
.
-
hibernate.validate_xml
-
Whether XML should be validated against their schema as Hibernate reads them.
hibernate.xml_mapping_enabled
-
Whether XML mappings should be processed.
A.7. Bytecode Manipulation Settings
hibernate.bytecode.provider
-
Selects a bytecode enhancement library.
At present only bytebuddy is supported, bytebuddy being the default since version 5.3.
hibernate.enhancer.enableAssociationManagement
-
Enable association management feature in runtime bytecode enhancement
A.8. Second-level Cache Settings
hibernate.cache.auto_evict_collection_cache
-
Enables the automatic eviction of a bidirectional association’s collection cache when an element in the
ManyToOne
collection is added, updated, or removed without properly managing the change on theOneToMany
side.
hibernate.cache.default_cache_concurrency_strategy
-
Specifies the
CacheConcurrencyStrategy
to use by default when an entity is marked@Cacheable
, but no concurrency strategy is explicitly specified via theCache
annotation.
hibernate.cache.region_prefix
-
The
CacheProvider
region name prefix
hibernate.cache.use_minimal_puts
-
Optimize interaction with the second-level cache to minimize writes, at the cost of an additional read before each write. This setting is useful if writes to the cache are much more expensive than reads from the cache, for example, if the cache is a distributed cache.
It’s not usually necessary to set this explicitly because, by default, it’s set to a sensible value by the second-level cache implementation.
hibernate.cache.use_query_cache
-
Enable the query results cache
hibernate.cache.use_reference_entries
-
Enable direct storage of entity references into the second level cache when applicable. This is appropriate only for immutable entities.
By default, entities are always stored in a «disassembled» form, that is, as a tuple of attribute values.
hibernate.cache.use_second_level_cache
-
When enabled, specifies that the second-level cache may be used.
By default, if the configured
RegionFactory
is not theNoCachingRegionFactory
, then the second-level cache is enabled. Otherwise, the second-level cache is disabled.
hibernate.cache.use_structured_entries
-
Enables the use of structured second-level cache entries. This makes the cache entries human-readable, but carries a performance cost.
hibernate.classcache
-
Entity cache configuration properties follow the pattern
hibernate.classcache.packagename.ClassName usage[, region]
whereusage
is the cache strategy used andregion
the cache region name
hibernate.collectioncache
-
Collection cache configuration properties follow the pattern
hibernate.collectioncache.packagename.ClassName.role usage[, region]
whereusage
is the cache strategy used andregion
the cache region name
hibernate.javax.cache.cache_manager
-
Allows providing
hibernate-jcache
with a custom JCacheCacheManager
.
hibernate.javax.cache.missing_cache_strategy
-
Define the behavior of the region factory when a cache is missing, i.e. when the cache was not created by the cache manager as it started. See
MissingCacheStrategy
for the various possible values. Default value isMissingCacheStrategy.FAIL
.
hibernate.javax.cache.provider
-
Allows providing
hibernate-jcache
with a custom JCacheCachingProvider
.
A.9. Audit/History Settings
org.hibernate.envers.allow_identifier_reuse
-
Guarantees proper validity audit strategy behavior when application reuses identifiers of deleted entities. Exactly one row with
null
end date exists for each identifier.
org.hibernate.envers.audit_strategy_validity_end_rev_field_name
-
Column name that will hold the end revision number in audit entities. Defaults to REVEND.
org.hibernate.envers.audit_strategy_validity_revend_timestamp_field_name
-
Column name of the timestamp of the end revision until which the data was valid. Defaults to REVEND_TSTMP.
org.hibernate.envers.audit_strategy_validity_revend_timestamp_legacy_placement
-
Whether to use legacy validity audit strategy revision end timestamp behavior where the field is not included as part of the joined entity inheritance subclass audit tables. Defaults to
true
.
org.hibernate.envers.audit_strategy_validity_revend_timestamp_numeric
-
Determines whether the timestamp of the end revision is stored as a numeric data type. Defaults to false.
org.hibernate.envers.audit_strategy_validity_store_revend_timestamp
-
Store the timestamp of the end revision, until which the data was valid, in addition to the end revision itself. Defaults to
false
.
org.hibernate.envers.audit_table_prefix
-
Audit table prefix. Empty by default.
org.hibernate.envers.audit_table_suffix
-
Audit table suffix. Defaults to _AUD.
org.hibernate.envers.cascade_delete_revision
-
Deletion of a revision entity will cause a foreign key constraint database error when at least one audit record exists for that revision. By enabling this feature, deletion of the revision entity will also force all audit records associated to that revision to be deleted via cascade. Defaults to false.
org.hibernate.envers.default_catalog
-
Default name of the catalog containing audit tables.
org.hibernate.envers.default_schema
-
Default name of the schema containing audit tables.
org.hibernate.envers.do_not_audit_optimistic_locking_field
-
Treats optimistic locking properties as unversioned. Defaults to
true
.
org.hibernate.envers.embeddable_set_ordinal_field_name
-
Name of column used for storing ordinal of the change in sets of embeddable elements. Defaults to SETORDINAL.
org.hibernate.envers.find_by_revision_exact_match
-
Forces
AuditReader#find
implementations that accept a revision-number argument to perform an exact match against the supplied revision number rather than potentially returning hits that are less-than or equal-to the supplied revision number. This option is meant to maintain backward compatibility while attempting to correct a bug in behavior without impacting existing users who may use the current behavior. Defaults to false.
org.hibernate.envers.global_relation_not_found_legacy_flag
-
Globally defines whether legacy relation not-found behavior should be used or not. Defaults to
true
. By specifyingtrue
, anyEntityNotFoundException
will be thrown unless the containing class or property explicitly specifies that use case to be ignored. Conversely, when specifying the valuefalse
, the inverse applies and requires explicitly specifying the use case as error so that the exception is thrown.
org.hibernate.envers.global_with_modified_flag
-
Globally activates modified properties flag feature. Defaults to
false
.
org.hibernate.envers.modified_column_naming_strategy
org.hibernate.envers.modified_flag_suffix
-
Suffix of modified flag columns. Defaults to _MOD.
org.hibernate.envers.original_id_prop_name
-
Original id property name name. Defaults to originalId.
org.hibernate.envers.revision_field_name
-
Revision field name. Defaults to REV.
org.hibernate.envers.revision_listener
-
Fully qualified class name of user defined revision listener.
org.hibernate.envers.revision_on_collection_change
-
Triggers revision generation when not-owned relation field changes. Defaults to
true
.
org.hibernate.envers.revision_sequence_nocache
-
Whether to apply a nocache configuration for the revision sequence. This is mostly interesting for testing.
org.hibernate.envers.revision_type_field_name
-
Revision type field name. Defaults to REVTYPE.
org.hibernate.envers.store_data_at_delete
-
Indicates whether entity data should be stored during removal. Defaults to
false
.
org.hibernate.envers.track_entities_changed_in_revision
-
Track entity names that have been changed during each revision. Defaults to
false
.
org.hibernate.envers.use_revision_entity_with_native_id
-
Use revision entity with native identifier generator. Defaults to
true
for backward compatibility.
A.10. Runtime Environment Settings
hibernate.classLoaders
-
Specifies a
collection
of theClassLoader
instances Hibernate should use for classloading and resource loading.
A.11. Miscellaneous Settings
jakarta.persistence.lock.scope
-
Set a default value for the hint
SpecHints.HINT_SPEC_LOCK_SCOPE
, used when the hint is not explicitly specified.See JPA 2 sections 8.2.1.9 and 3.4.4.3
jakarta.persistence.lock.timeout
-
Set a default value for the hint
SpecHints.HINT_SPEC_LOCK_TIMEOUT
, used when the hint is not explicitly specified.See JPA 2 sections 8.2.1.9 and 3.4.4.3
hibernate.allow_refresh_detached_entity
-
Values are
true
, which allows refreshing a detached instance andfalse
, which does not. When refreshing is disallowed, anIllegalArgumentException
is thrown.The default behavior is to allow refreshing a detached instance unless Hibernate is bootstrapped via JPA.
hibernate.current_session_context_class
-
Specifies a
CurrentSessionContext
for scoping the current session, either:-
jta
,thread
, ormanaged
, or -
the name of a class implementing
org.hibernate.context.spi.CurrentSessionContext
. If this property is not set, but JTA support is enabled, thenJTASessionContext
is used by default.
-
hibernate.discard_pc_on_close
hibernate.event.listener
-
Event listener configuration properties follow the pattern
hibernate.event.listener.eventType packageName.ClassName1, packageName.ClassName2
hibernate.event.merge.entity_copy_observer
-
Setting that specifies how Hibernate will respond when multiple representations of the same persistent entity («entity copy») are detected while merging.
The possible values are:
-
disallow (the default): throws
IllegalStateException
if an entity copy is detected -
allow: performs the merge operation on each entity copy that is detected
-
log: (provided for testing only) performs the merge operation on each entity copy that is detected and logs information about the entity copies. This setting requires DEBUG logging be enabled for
EntityCopyAllowedLoggedObserver
.
Alternatively, the application may customize the behavior by providing an implementation of
EntityCopyObserver
and setting the property «hibernate.event.merge.entity_copy_observer» to the class name.When this property is set to
allow
orlog
, Hibernate will merge each entity copy detected while cascading the merge operation. In the process of merging each entity copy, Hibernate will cascade the merge operation from each entity copy to its associations withCascadeType.MERGE
orCascadeType.ALL
. The entity state resulting from merging an entity copy will be overwritten when another entity copy is merged. -
hibernate.identifier_generator_strategy_provider
hibernate.loader.delay_entity_loader_creations
-
When
true
, the default, the loaders are only created on first access; this ensures that all access patterns which are not useful to the application are never instantiated, possibly saving a substantial amount of memory for applications having many entities. The only exception is the loader forLockMode.NONE
, which will always be eagerly initialized; this is necessary to detect mapping errors.false
indicates that all loaders should be created up front; this will consume more memory but ensures all necessary memory is allocated right away.
hibernate.use_identifier_rollback
-
When enabled, specifies that the generated identifier of an entity is unset when the entity is deleted.
A.12. Query Settings
hibernate.criteria.copy_tree
-
If disabled, it’s assumed that the client does not mutate the criteria query after calling
createQuery()
. Thus, in the interest of performance, no copy is created.The default behavior depends on how Hibernate is bootstrapped:
-
When bootstrapping Hibernate through the native bootstrap APIs, this setting is disabled, that is, no copy of the criteria query object is made.
-
When bootstrapping Hibernate through the JPA SPI, this setting is enabled so that criteria query objects are copied, as required by the JPA specification.
-
hibernate.order_by.default_null_ordering
-
Specifies the default precedence of null values in the HQL
ORDER BY
clause, eithernone
,first
, orlast
.The default is
none
.
hibernate.query.hql.translator
-
Specifies a
HqlTranslator
to use for HQL query translation.
hibernate.query.immutable_entity_update_query_handling_mode
-
-
"warning"
specifies that a warning log message is issued when an immutable entity is to be updated via a bulk update statement, and -
"exception"
specifies that aHibernateException
should be thrown.
By default, a warning is logged.
-
hibernate.query.in_clause_parameter_padding
-
Determines how parameters occurring in a SQL
IN
predicate are expanded. By default, theIN
predicate expands to include sufficient bind parameters to accommodate the specified arguments.However, for database systems supporting execution plan caching, there’s a better chance of hitting the cache if the number of possible
IN
clause parameter list lengths is smaller.When this setting is enabled, we expand the number of bind parameters to an integer power of two: 4, 8, 16, 32, 64. Thus, if 5, 6, or 7 arguments are bound to a parameter, a SQL statement with 8 bind parameters in the
IN
clause will be used, and null will be bound to the left-over parameters.
hibernate.query.insert_strategy
-
Defines the «global» strategy to use for handling HQL and Criteria insert queries. Specifies a
SqmMultiTableInsertStrategy
.
hibernate.query.mutation_strategy
-
Defines the «global» strategy to use for handling HQL and Criteria mutation queries. Specifies a
SqmMultiTableMutationStrategy
..
hibernate.query.plan_cache_enabled
-
When enabled, specifies that query plans should be cached.
hibernate.query.proc.callable_named_params_enabled
hibernate.query.startup_check
-
When enabled, specifies that named queries be checked during startup.
By default, named queries are checked at startup.
Mainly intended for use in test environments.
A.13. Schema Tooling Settings
jakarta.persistence.create-database-schemas
-
The JPA variant of
HBM2DDL_CREATE_NAMESPACES
used to specify whether database schemas used in the mapping model should be created on export in addition to creating the tables, sequences, etc.The default is
false
, meaning to not create schemas
jakarta.persistence.schema-generation.create-script-source
-
Specifies the CREATE script file as either a
Reader
configured for reading the DDL script file or a string designating a fileURL
for the DDL script.Hibernate historically also accepted
HBM2DDL_IMPORT_FILES
for a similar purpose. This setting is now preferred.
jakarta.persistence.schema-generation.create-source
-
Specifies whether schema generation commands for schema creation are to be determined based on object/relational mapping metadata, DDL scripts, or a combination of the two. See
SourceType
for the list of legal values.If no value is specified, a default is inferred as follows:
-
if source scripts are specified via «jakarta.persistence.schema-generation.create-script-source», then
"script"
is assumed, or -
otherwise,
"metadata"
is assumed.
-
jakarta.persistence.schema-generation.drop-script-source
-
Specifies the DROP script file as either a
Reader
configured for reading the DDL script file or a string designating a fileURL
for the DDL script.
jakarta.persistence.schema-generation.drop-source
-
Specifies whether schema generation commands for schema dropping are to be determined based on object/relational mapping metadata, DDL scripts, or a combination of the two. See
SourceType
for the list of legal values.If no value is specified, a default is inferred as follows:
-
if source scripts are specified via «jakarta.persistence.schema-generation.drop-script-source», then «script» is assumed, or
-
otherwise, «metadata» is assumed.
-
jakarta.persistence.schema-generation.scripts.action
-
Specifies what type of schema tooling action should be written to script files.
Valid options are enumerated by
Action
.If no value is specified, the default is
"none"
.
jakarta.persistence.schema-generation.scripts.create-target
-
For cases where «jakarta.persistence.schema-generation.scripts.action» indicates that schema creation commands should be written to a script file, this setting specifies either a
Writer
configured for output of the DDL script or a string specifying the file URL for the DDL script.
jakarta.persistence.schema-generation.scripts.drop-target
-
For cases where «jakarta.persistence.schema-generation.scripts.action» indicates that schema drop commands should be written to a script file, this setting specifies either a
Writer
configured for output of the DDL script or a string specifying the file URL for the DDL script.
jakarta.persistence.sql-load-script-source
-
JPA-standard variant of
HBM2DDL_IMPORT_FILES
for specifying a database initialization script to be run as part of schema-exportSpecifies a
Reader
configured for reading of the SQL load script or a string designating theURL
for the SQL load script.
hibernate.dialect.storage_engine
-
Specifies the default storage engine for a relational databases that supports multiple storage engines. This property must be set either as an
Environment
variable or JVM System Property, since theDialect
is instantiated before Hibernate property resolution.
hibernate.hbm2ddl.charset_name
-
The name of the charset used by the schema generation resource.
By default, the JVM default charset is used.
hibernate.hbm2ddl.create_namespaces
-
Specifies whether to automatically create also the database schema/catalog. The default is false.
hibernate.hbm2ddl.default_constraint_mode
hibernate.hbm2ddl.delimiter
-
Identifies the delimiter to use to separate schema management statements in script outputs.
hibernate.hbm2ddl.halt_on_error
-
When enabled, specifies that the schema migration tool should halt on any error, terminating the bootstrap process.
hibernate.hbm2ddl.import_files
-
Specifies a comma-separated list of file names of scripts containing SQL DML statements that should be executed after schema export completes. The order of the scripts is significant, with the first script in the list being executed first.
The scripts are only executed if the schema is created by Hibernate, that is, if «hibernate.hbm2ddl.auto» is set to
create
orcreate-drop
.The default value is
/import.sql
.
hibernate.hbm2ddl.schema-generation.script.append
-
For cases where the «jakarta.persistence.schema-generation.scripts.action» value indicates that schema commands should be written to DDL script file, specifies if schema commands should be appended to the end of the file rather than written at the beginning of the file.
Values are:
true
for appending schema commands to the end of the file,false
for writing schema commands at the beginning.
hibernate.hbm2ddl.schema_filter_provider
-
Used to specify the
SchemaFilterProvider
to be used by create, drop, migrate and validate operations on the database schema. ASchemaFilterProvider
provides filters that can be used to limit the scope of these operations to specific namespaces, tables and sequences. All objects are included by default.
hibernate.hql.bulk_id_strategy.global_temporary.create_tables
-
Allows creation of global temporary tables at application startup to be disabled. By default, table creation is enabled.
hibernate.hql.bulk_id_strategy.global_temporary.drop_tables
-
Allows dropping of global temporary tables at application shutdown to be disabled. By default, table dropping is enabled.
hibernate.hql.bulk_id_strategy.local_temporary.drop_tables
-
Allows dropping of local temporary tables at transaction commit to be enabled. By default, table dropping is disabled, and the database will drop the temporary tables automatically.
hibernate.hql.bulk_id_strategy.persistent.create_tables
-
Allows creation of persistent temporary tables at application startup to be disabled. By default, table creation is enabled.
hibernate.hql.bulk_id_strategy.persistent.drop_tables
-
Allows dropping of persistent temporary tables at application shutdown to be disabled. By default, table dropping is enabled.
hibernate.schema_update.unique_constraint_strategy
-
Unique columns and unique keys both use unique constraints in most dialects. The schema exporter must create these constraints, but database support for finding existing constraints is extremely inconsistent. Worse, unique constraints without explicit names are assigned names with randomly generated characters.
Therefore, select from these strategies:
-
DROP_RECREATE_QUIETLY: Attempt to drop, then (re-)create each unique constraint, ignoring any exceptions thrown. This is the default.
-
RECREATE_QUIETLY: Attempt to (re-)create unique constraints, ignoring exceptions thrown if the constraint already existed.
-
SKIP: Do not attempt to create unique constraints on a schema update.
-
hibernate.synonyms
-
If enabled, allows schema update and validation to support synonyms. Due to the possibility that this would return duplicate tables (especially in Oracle), this is disabled by default.
A.14. Hibernate Spatial Settings
hibernate.integration.spatial.enabled
-
The name of the configuration setting used to control whether the spatial integration is enabled. Default is true
hibernate.spatial.connection_finder
-
The canonical class name of the Oracle ConnectionFinder implementation that will be used by the Oracle spatial dialects
hibernate.spatial.db2.srid
-
SRID to use for the DB2 Spatial Dialects.
A.15. Statistics Settings
hibernate.generate_statistics
-
When enabled, specifies that statistics should be collected.
hibernate.statistics.query_max_size
-
This setting controls the number of
QueryStatistics
entries that will be stored by the HibernateStatistics
object.The default value is 5000.
hibernate.stats.factory
-
When statistics are enabled, names the
StatisticsFactory
to use. Recognizes a class name as well as an instance ofStatisticsFactory
.Allows customization of how the Hibernate Statistics are collected.
A.16. Jakarta Validation Integeration Settings
jakarta.persistence.validation.factory
-
Used to pass along any discovered
ValidatorFactory
.
jakarta.persistence.validation.group.pre-persist
-
Used to coordinate with bean validators.
See JPA 2 section 8.2.1.9
jakarta.persistence.validation.group.pre-remove
-
Used to coordinate with bean validators.
See JPA 2 section 8.2.1.9
jakarta.persistence.validation.group.pre-update
-
Used to coordinate with bean validators.
See JPA 2 section 8.2.1.9
jakarta.persistence.validation.mode
-
Indicates which form of automatic validation is in effect as per the rules defined in JPA 2 section 3.6.1.1.
See JPA 2 sections 9.4.3 and 8.2.1.8
hibernate.check_nullability
-
Enable nullability checking, raises an exception if an attribute marked as not null is null at runtime.
Defaults to disabled if Bean Validation is present in the classpath and annotations are used, or enabled otherwise.
Appendix B: Legacy BasicType resolution
Versions prior to 6.0 statically combined the JavaType
, JdbcType
, BasicValueConverter
and
MutabilityPlan
aspects within the org.hibernate.type.BasicType
contract. Hibernate’s legacy strategy for resolving
a basic type is based on finding the implementation of org.hibernate.type.BasicType
to use.
This appendix will describe the legacy approach for influencing the mapping of basic types.
Generally speaking, this resolution uses an internal registry of BasicType
implementations
registered under one-or-more «registration keys». The tables in Hibernate-provided BasicTypeReferences describe
the initial set of BasicType
references registered by Hibernate. BasicTypeRegistry
describes this BasicTypeRegistry
.
Users can also override mappings in the BasicTypeRegistry
or extend them to map new types, as described
in Custom BasicTypes.
B.1. Hibernate-provided BasicTypeReferences
StandardBasicTypes constant | JDBC type | Java type | BasicTypeRegistry key(s) |
---|---|---|---|
STRING |
VARCHAR |
java.lang.String |
string, java.lang.String |
MATERIALIZED_CLOB |
CLOB |
java.lang.String |
materialized_clob |
MATERIALIZED_CLOB_CHAR_ARRAY |
CHAR |
char[] |
materialized_clob_char_array |
MATERIALIZED_CLOB_CHARACTER_ARRAY |
CLOB |
java.lang.Character[] |
materialized_clob_character_array |
TEXT |
LONGVARCHAR |
java.lang.String |
text |
CHARACTER |
CHAR |
char, java.lang.Character |
character, char, java.lang.Character |
BOOLEAN |
BOOLEAN |
boolean, java.lang.Boolean |
boolean, java.lang.Boolean |
NUMERIC_BOOLEAN |
TINYINT, 0 is false, 1 is true |
boolean, java.lang.Boolean |
numeric_boolean |
YES_NO |
CHAR, ‘N’/’n’ is false, ‘Y’/’y’ is true. The uppercase value is written to the database. |
boolean, java.lang.Boolean |
yes_no |
TRUE_FALSE |
CHAR, ‘F’/’f’ is false, ‘T’/’t’ is true. The uppercase value is written to the database. |
boolean, java.lang.Boolean |
true_false |
BYTE |
TINYINT |
byte, java.lang.Byte |
byte, java.lang.Byte |
SHORT |
SMALLINT |
short, java.lang.Short |
short, java.lang.Short |
INTEGER |
INTEGER |
int, java.lang.Integer |
integer, int, java.lang.Integer |
LONG |
BIGINT |
long, java.lang.Long |
long, java.lang.Long |
FLOAT |
FLOAT |
float, java.lang.Float |
float, java.lang.Float |
DOUBLE |
DOUBLE |
double, java.lang.Double |
double, java.lang.Double |
BIG_INTEGER |
NUMERIC |
java.math.BigInteger |
big_integer, java.math.BigInteger |
BIG_DECIMAL |
NUMERIC |
java.math.BigDecimal |
big_decimal, java.math.bigDecimal |
TIMESTAMP |
TIMESTAMP |
java.util.Date |
timestamp, java.sql.Timestamp, java.util.Date |
TIME |
TIME |
java.util.Date |
time, java.sql.Time |
DATE |
DATE |
java.util.Date |
date, java.sql.Date |
CALENDAR |
TIMESTAMP |
java.util.Calendar |
calendar, java.util.Calendar, java.util.GregorianCalendar |
CALENDAR_DATE |
DATE |
java.util.Calendar |
calendar_date |
CALENDAR_TIME |
TIME |
java.util.Calendar |
calendar_time |
CURRENCY |
VARCHAR |
java.util.Currency |
currency, java.util.Currency |
LOCALE |
VARCHAR |
java.util.Locale |
locale, java.util.Locale |
TIMEZONE |
VARCHAR, using the TimeZone ID |
java.util.TimeZone |
timezone, java.util.TimeZone |
URL |
VARCHAR |
java.net.URL |
url, java.net.URL |
CLASS |
VARCHAR (class FQN) |
java.lang.Class |
class, java.lang.Class |
BLOB |
BLOB |
java.sql.Blob |
blob, java.sql.Blob |
CLOB |
CLOB |
java.sql.Clob |
clob, java.sql.Clob |
BINARY |
VARBINARY |
byte[] |
binary, byte[] |
MATERIALIZED_BLOB |
BLOB |
byte[] |
materialized_blob |
IMAGE |
LONGVARBINARY |
byte[] |
image |
BINARY_WRAPPER |
VARBINARY |
java.lang.Byte[] |
binary_wrapper, wrapper-binary, Byte[], java.lang.Byte[] |
MATERIALIZED_BLOB_WRAPPER |
BLOB |
java.lang.Byte[] |
materialized_blob_wrapper |
CHAR_ARRAY |
VARCHAR |
char[] |
characters, char[] |
CHARACTER_ARRAY |
VARCHAR |
java.lang.Character[] |
wrapper-characters, Character[], java.lang.Character[] |
UUID |
UUID or BINARY |
java.util.UUID |
uuid, java.util.UUID, pg-uuid |
UUID_BINARY |
BINARY |
java.util.UUID |
uuid-binary, java.util.UUID |
UUID_CHAR |
CHAR, can also read VARCHAR |
java.util.UUID |
uuid-char |
SERIALIZABLE |
VARBINARY |
implementors of java.lang.Serializable |
Unlike the other value types, multiple instances of this type are registered. It is registered once under java.io.Serializable, and registered under the specific java.io.Serializable implementation class names. |
NSTRING |
NVARCHAR |
java.lang.String |
nstring |
NTEXT |
LONGNVARCHAR |
java.lang.String |
ntext |
NCLOB |
NCLOB |
java.sql.NClob |
nclob, java.sql.NClob |
MATERIALIZED_NCLOB |
NCLOB |
java.lang.String |
materialized_nclob |
MATERIALIZED_NCLOB_CHAR_ARRAY |
NCHAR |
char[] |
materialized_nclob_char_array |
CHARACTER_NCHAR |
NCHAR |
java.lang.Character |
ncharacter |
MATERIALIZED_NCLOB_CHARACTER_ARRAY |
NCLOB |
java.lang.Character[] |
materialized_nclob_character_array |
ROW_VERSION |
VARBINARY |
byte[] |
row_version |
OBJECT_TYPE |
VARCHAR |
implementors of java.lang.Serializable |
object, java.lang.Object |
Hibernate type (org.hibernate.type package) | JDBC type | Java type | BasicTypeRegistry key(s) |
---|---|---|---|
DURATION |
NUMERIC |
java.time.Duration |
Duration, java.time.Duration |
INSTANT |
TIMESTAMP_UTC |
java.time.Instant |
Instant, java.time.Instant |
LOCAL_DATE_TIME |
TIMESTAMP |
java.time.LocalDateTime |
LocalDateTime, java.time.LocalDateTime |
LOCAL_DATE |
DATE |
java.time.LocalDate |
LocalDate, java.time.LocalDate |
LOCAL_TIME |
TIME |
java.time.LocalTime |
LocalTime, java.time.LocalTime |
OFFSET_DATE_TIME |
TIMESTAMP_WITH_TIMEZONE |
java.time.OffsetDateTime |
OffsetDateTime, java.time.OffsetDateTime |
OFFSET_DATE_TIME_WITH_TIMEZONE |
TIMESTAMP_WITH_TIMEZONE |
java.time.OffsetDateTime |
OffsetDateTime, java.time.OffsetDateTime |
OFFSET_DATE_TIME_WITHOUT_TIMEZONE |
TIMESTAMP |
java.time.OffsetDateTime |
OffsetDateTime, java.time.OffsetDateTime |
OFFSET_TIME |
TIME |
java.time.OffsetTime |
OffsetTime, java.time.OffsetTime |
ZONED_DATE_TIME |
TIMESTAMP_WITH_TIMEZONE |
java.time.ZonedDateTime |
ZonedDateTime, java.time.ZonedDateTime |
ZONED_DATE_TIME_WITH_TIMEZONE |
TIMESTAMP_WITH_TIMEZONE |
java.time.ZonedDateTime |
ZonedDateTimeWithTimezone |
ZONED_DATE_TIME_WITHOUT_TIMEZONE |
TIMESTAMP |
java.time.ZonedDateTime |
ZonedDateTimeWithoutTimezone |
ZONE_OFFSET |
VARCHAR |
java.time.ZoneOffset |
ZoneOffset, java.time.ZoneOffset |
B.2. BasicTypeRegistry
We said before that a Hibernate type is not a Java type, nor an SQL type, but that it understands both and performs the marshalling between them.
But looking at the basic type mappings from the previous examples,
how did Hibernate know to use its org.hibernate.type.StandardBasicTypes.STRING
for mapping for java.lang.String
attributes,
or its org.hibernate.type.StandardBasicTypes.INTEGER
for mapping java.lang.Integer
attributes?
The answer lies in a service inside Hibernate called the org.hibernate.type.BasicTypeRegistry
, which maintains a
map of org.hibernate.type.BasicType
and org.hibernate.type.BasicTypeReference
instances keyed by a name.
We will see later, in the Explicit BasicTypes section, that we can explicitly tell Hibernate which BasicType to use for a particular attribute.
But first, let’s explore how implicit resolution works and how applications can adjust the implicit resolution.
A thorough discussion of |
As an example, take a String attribute such as we saw before with Product#sku.
Since there is no explicit type mapping, Hibernate looks to the BasicTypeRegistry
to find the registered
mapping for java.lang.String
.
As a baseline within BasicTypeRegistry
, Hibernate follows the recommended mappings of JDBC for Java types.
JDBC recommends mapping Strings to VARCHAR, which is the exact mapping that StringType
handles.
So that is the baseline mapping within BasicTypeRegistry
for Strings.
Applications can also extend (add new BasicType
registrations) or override (replace an existing BasicType
registration) using one of the
MetadataBuilder#applyBasicType
methods or the MetadataBuilder#applyTypes
method during bootstrap.
For more details, see Custom BasicTypes section.
B.3. Explicit BasicTypes
Sometimes you want a particular attribute to be handled differently.
Occasionally Hibernate will implicitly pick a BasicType
that you do not want (and for some reason you do not want to adjust the BasicTypeRegistry
).
In these cases, you must explicitly tell Hibernate the BasicType
to use, via the org.hibernate.annotations.Type
annotation.
Example 693. Using @org.hibernate.annotations.Type
@Entity(name = "Product")
public class Product {
@Id
private Integer id;
private String sku;
@Type(
value = UserTypeLegacyBridge.class,
parameters = @Parameter(name = UserTypeLegacyBridge.TYPE_NAME_PARAM_KEY, value = "nstring")
)
private String name;
@Type(
value = UserTypeLegacyBridge.class,
parameters = @Parameter(name = UserTypeLegacyBridge.TYPE_NAME_PARAM_KEY, value = "materialized_nclob")
)
private String description;
}
This tells Hibernate to store the Strings as nationalized data.
This is just for illustration purposes; for better ways to indicate nationalized character data see Handling nationalized character data section.
Additionally, the description is to be handled as a LOB. Again, for better ways to indicate LOBs see Handling LOB data section.
The org.hibernate.annotations.Type#value
attribute can refers to a org.hibernate.type.UserType
class
which can be configured further by specifying org.hibernate.annotations.Type#parameters
.
The special user type org.hibernate.usertype.UserTypeLegacyBridge
provides a way to bridge the gap between the named
type use before Hibernate 6.0 and the new strongly typed nature of org.hibernate.annotations.Type
.
B.4. Custom BasicTypes
Hibernate makes it relatively easy for developers to create their own basic type mappings type.
For example, you might want to persist properties of type java.util.BigInteger
to VARCHAR
columns, or support completely new types.
There are two approaches to developing a custom type:
-
implementing a
BasicType
and registering it -
implementing a
UserType
which doesn’t require type registration
As a means of illustrating the different approaches, let’s consider a use case where we need to support a java.util.BitSet
mapping that’s stored as a VARCHAR.
B.4.1. Implementing a BasicType
The first approach is to directly implement the BasicType
interface.
Because the |
First, we need to extend the AbstractSingleColumnStandardBasicType
like this:
Example 694. Custom BasicType
implementation
public class BitSetType
extends AbstractSingleColumnStandardBasicType<BitSet> {
public static final BitSetType INSTANCE = new BitSetType();
public BitSetType() {
super( VarcharJdbcType.INSTANCE, BitSetJavaType.INSTANCE );
}
@Override
public String getName() {
return "bitset";
}
}
The AbstractSingleColumnStandardBasicType
requires an jdbcType
and a javaType
.
The jdbcType
is VarcharJdbcType.INSTANCE
because the database column is a VARCHAR.
On the Java side, we need to use a BitSetJavaType
instance which can be implemented like this:
Example 695. Custom JavaType
implementation
public class BitSetJavaType extends AbstractClassJavaType<BitSet> {
public static final BitSetJavaType INSTANCE = new BitSetJavaType();
public BitSetJavaType() {
super(BitSet.class);
}
@Override
public MutabilityPlan<BitSet> getMutabilityPlan() {
return BitSetMutabilityPlan.INSTANCE;
}
@Override
public JdbcType getRecommendedJdbcType(JdbcTypeIndicators indicators) {
return indicators.getTypeConfiguration()
.getJdbcTypeRegistry()
.getDescriptor(Types.VARCHAR);
}
@Override
public String toString(BitSet value) {
return BitSetHelper.bitSetToString(value);
}
@Override
public BitSet fromString(CharSequence string) {
return BitSetHelper.stringToBitSet(string.toString());
}
@SuppressWarnings("unchecked")
public <X> X unwrap(BitSet value, Class<X> type, WrapperOptions options) {
if (value == null) {
return null;
}
if (BitSet.class.isAssignableFrom(type)) {
return (X) value;
}
if (String.class.isAssignableFrom(type)) {
return (X) toString(value);
}
if (type.isArray()) {
if (type.getComponentType() == byte.class) {
return (X) value.toByteArray();
}
}
throw unknownUnwrap(type);
}
public <X> BitSet wrap(X value, WrapperOptions options) {
if (value == null) {
return null;
}
if (value instanceof CharSequence) {
return fromString((CharSequence) value);
}
if (value instanceof BitSet) {
return (BitSet) value;
}
throw unknownWrap(value.getClass());
}
}
The unwrap()
method is used when passing a BitSet
as a PreparedStatement
bind parameter, while the wrap()
method is used to transform the JDBC column value object (e.g. String
in our case) to the actual mapping object type (e.g. BitSet
in this example).
The BasicType
must be registered, and this can be done at bootstrapping time:
Example 696. Register a Custom BasicType
implementation
configuration.registerTypeContributor( (typeContributions, serviceRegistry) -> {
typeContributions.contributeType( BitSetType.INSTANCE );
} );
or using the MetadataBuilder
ServiceRegistry standardRegistry =
new StandardServiceRegistryBuilder().build();
MetadataSources sources = new MetadataSources( standardRegistry );
MetadataBuilder metadataBuilder = sources.getMetadataBuilder();
metadataBuilder.applyBasicType( BitSetType.INSTANCE );
With the new BitSetType
being registered as bitset
, the entity mapping looks like this:
Example 697. Custom BasicType
mapping
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
@Type(
value = UserTypeLegacyBridge.class,
parameters = @Parameter(name = UserTypeLegacyBridge.TYPE_NAME_PARAM_KEY, value = "bitset")
)
private BitSet bitSet;
public Integer getId() {
return id;
}
//Getters and setters are omitted for brevity
}
To validate this new BasicType
implementation, we can test it as follows:
Example 698. Persisting the custom BasicType
BitSet bitSet = BitSet.valueOf( new long[] {1, 2, 3} );
doInHibernate( this::sessionFactory, session -> {
Product product = new Product( );
product.setId( 1 );
product.setBitSet( bitSet );
session.persist( product );
} );
doInHibernate( this::sessionFactory, session -> {
Product product = session.get( Product.class, 1 );
assertEquals(bitSet, product.getBitSet());
} );
When executing this unit test, Hibernate generates the following SQL statements:
Example 699. Persisting the custom BasicType
DEBUG SQL:92 -
insert
into
Product
(bitSet, id)
values
(?, ?)
TRACE BasicBinder:65 - binding parameter [1] as [VARCHAR] - [{0, 65, 128, 129}]
TRACE BasicBinder:65 - binding parameter [2] as [INTEGER] - [1]
DEBUG SQL:92 -
select
bitsettype0_.id as id1_0_0_,
bitsettype0_.bitSet as bitSet2_0_0_
from
Product bitsettype0_
where
bitsettype0_.id=?
TRACE BasicBinder:65 - binding parameter [1] as [INTEGER] - [1]
TRACE BasicExtractor:61 - extracted value ([bitSet2_0_0_] : [VARCHAR]) - [{0, 65, 128, 129}]
As you can see, the BitSetType
takes care of the Java-to-SQL and SQL-to-Java type conversion.
B.4.2. Implementing a UserType
The second approach is to implement the UserType
interface.
Example 700. Custom UserType
implementation
public class BitSetUserType implements UserType<BitSet> {
private static final Logger log = Logger.getLogger(BitSetUserType.class);
@Override
public int getSqlType() {
return Types.VARCHAR;
}
@Override
public Class<BitSet> returnedClass() {
return BitSet.class;
}
@Override
public boolean equals(BitSet x, BitSet y) {
return Objects.equals(x, y);
}
@Override
public int hashCode(BitSet x) {
return Objects.hashCode(x);
}
@Override
public BitSet nullSafeGet(ResultSet rs, int position,
SharedSessionContractImplementor session, Object owner)
throws SQLException {
String columnValue = rs.getString(position);
if (rs.wasNull()) {
columnValue = null;
}
log.debugv("Result set column {0} value is {1}", position, columnValue);
return BitSetHelper.stringToBitSet(columnValue);
}
@Override
public void nullSafeSet(PreparedStatement st, BitSet value, int index,
SharedSessionContractImplementor session)
throws SQLException {
if (value == null) {
log.debugv("Binding null to parameter {0} ",index);
st.setNull(index, Types.VARCHAR);
}
else {
String stringValue = BitSetHelper.bitSetToString(value);
log.debugv("Binding {0} to parameter {1} ", stringValue, index);
st.setString(index, stringValue);
}
}
@Override
public BitSet deepCopy(BitSet bitSet) {
return bitSet == null ? null : (BitSet) bitSet.clone();
}
@Override
public boolean isMutable() {
return true;
}
@Override
public Serializable disassemble(BitSet value) {
return deepCopy(value);
}
@Override
public BitSet assemble(Serializable cached, Object owner) {
return deepCopy((BitSet) cached);
}
}
The entity mapping looks as follows:
Example 701. Custom UserType
mapping
@Entity(name = "Product")
public static class Product {
@Id
private Integer id;
@Type(BitSetUserType.class)
@Column(name = "bitset_col")
private BitSet bitSet;
//Constructors, getters, and setters are omitted for brevity
}
In this example, the UserType
is registered under the bitset
name, and this is done like this:
Example 702. Register a Custom UserType
implementation
configuration.registerTypeContributor( (typeContributions, serviceRegistry) -> {
typeContributions.contributeType( BitSetUserType.INSTANCE, "bitset");
} );
or using the MetadataBuilder
ServiceRegistry standardRegistry =
new StandardServiceRegistryBuilder().build();
MetadataSources sources = new MetadataSources(standardRegistry);
MetadataBuilder metadataBuilder = sources.getMetadataBuilder();
metadataBuilder.applyBasicType(new BitSetUserType(), "bitset");
When running the previous test case against the BitSetUserType
entity mapping, Hibernate executed the following SQL statements:
Example 703. Persisting the custom BasicType
DEBUG SQL:92 -
insert
into
Product
(bitSet, id)
values
(?, ?)
DEBUG BitSetUserType:71 - Binding 1,10,11 to parameter 1
TRACE BasicBinder:65 - binding parameter [2] as [INTEGER] - [1]
DEBUG SQL:92 -
select
bitsetuser0_.id as id1_0_0_,
bitsetuser0_.bitSet as bitSet2_0_0_
from
Product bitsetuser0_
where
bitsetuser0_.id=?
TRACE BasicBinder:65 - binding parameter [1] as [INTEGER] - [1]
DEBUG BitSetUserType:56 - Result set column bitSet2_0_0_ value is 1,10,11
Appendix C: Legacy Hibernate Native Queries
C.1. Legacy named SQL queries
Named SQL queries can also be defined during mapping and called in exactly the same way as a named HQL query.
In this case, you do not need to call addEntity()
anymore.
Example 704. Named sql query using the <sql-query>
mapping element
<sql-query name = "persons">
<return alias="person" class="eg.Person"/>
SELECT person.NAME AS {person.name},
person.AGE AS {person.age},
person.SEX AS {person.sex}
FROM PERSON person
WHERE person.NAME LIKE :namePattern
</sql-query>
Example 705. Execution of a named query
List people = session
.getNamedQuery( "persons" )
.setParameter( "namePattern", namePattern )
.setMaxResults( 50 )
.list();
The <return-join>
element is use to join associations and the <load-collection>
element is used to define queries which initialize collections.
Example 706. Named sql query with association
<sql-query name = "personsWith">
<return alias="person" class="eg.Person"/>
<return-join alias="address" property="person.mailingAddress"/>
SELECT person.NAME AS {person.name},
person.AGE AS {person.age},
person.SEX AS {person.sex},
address.STREET AS {address.street},
address.CITY AS {address.city},
address.STATE AS {address.state},
address.ZIP AS {address.zip}
FROM PERSON person
JOIN ADDRESS address
ON person.ID = address.PERSON_ID AND address.TYPE='MAILING'
WHERE person.NAME LIKE :namePattern
</sql-query>
A named SQL query may return a scalar value.
You must declare the column alias and Hibernate type using the <return-scalar>
element:
Example 707. Named query returning a scalar
<sql-query name = "mySqlQuery">
<return-scalar column = "name" type="string"/>
<return-scalar column = "age" type="long"/>
SELECT p.NAME AS name,
p.AGE AS age,
FROM PERSON p WHERE p.NAME LIKE 'Hiber%'
</sql-query>
You can externalize the resultset mapping information in a <resultset>
element which will allow you to either reuse them across several named queries or through the setResultSetMapping()
API.
Example 708. <resultset> mapping used to externalize mapping information
<resultset name = "personAddress">
<return alias="person" class="eg.Person"/>
<return-join alias="address" property="person.mailingAddress"/>
</resultset>
<sql-query name = "personsWith" resultset-ref="personAddress">
SELECT person.NAME AS {person.name},
person.AGE AS {person.age},
person.SEX AS {person.sex},
address.STREET AS {address.street},
address.CITY AS {address.city},
address.STATE AS {address.state},
address.ZIP AS {address.zip}
FROM PERSON person
JOIN ADDRESS address
ON person.ID = address.PERSON_ID AND address.TYPE='MAILING'
WHERE person.NAME LIKE :namePattern
</sql-query>
You can, alternatively, use the resultset mapping information in your hbm files directly in Java code.
Example 709. Programmatically specifying the result mapping information
List cats = session
.createSQLQuery( "select {cat.*}, {kitten.*} from cats cat, cats kitten where kitten.mother = cat.id" )
.setResultSetMapping( "catAndKitten" )
.list();
C.2. Legacy return-property to explicitly specify column/alias names
You can explicitly tell Hibernate what column aliases to use with <return-property>
, instead of using the {}
syntax to let Hibernate inject its own aliases.
For example:
<sql-query name = "mySqlQuery">
<return alias = "person" class = "eg.Person">
<return-property name = "name" column = "myName"/>
<return-property name = "age" column = "myAge"/>
<return-property name = "sex" column = "mySex"/>
</return>
SELECT person.NAME AS myName,
person.AGE AS myAge,
person.SEX AS mySex,
FROM PERSON person WHERE person.NAME LIKE :name
</sql-query>
<return-property>
also works with multiple columns.
This solves a limitation with the {}
syntax which cannot allow fine grained control of multi-column properties.
<sql-query name = "organizationCurrentEmployments">
<return alias = "emp" class = "Employment">
<return-property name = "salary">
<return-column name = "VALUE"/>
<return-column name = "CURRENCY"/>
</return-property>
<return-property name = "endDate" column = "myEndDate"/>
</return>
SELECT EMPLOYEE AS {emp.employee}, EMPLOYER AS {emp.employer},
STARTDATE AS {emp.startDate}, ENDDATE AS {emp.endDate},
REGIONCODE as {emp.regionCode}, EID AS {emp.id}, VALUE, CURRENCY
FROM EMPLOYMENT
WHERE EMPLOYER = :id AND ENDDATE IS NULL
ORDER BY STARTDATE ASC
</sql-query>
In this example <return-property>
was used in combination with the {}
syntax for injection.
This allows users to choose how they want to refer column and properties.
If your mapping has a discriminator you must use <return-discriminator>
to specify the discriminator column.
C.3. Legacy stored procedures for querying
Hibernate provides support for queries via stored procedures and functions.
Most of the following documentation is equivalent for both.
The stored procedure/function must return a resultset as the first out-parameter to be able to work with Hibernate.
An example of such a stored function in Oracle 9 and higher is as follows:
CREATE OR REPLACE FUNCTION selectAllEmployments
RETURN SYS_REFCURSOR
AS
st_cursor SYS_REFCURSOR;
BEGIN
OPEN st_cursor FOR
SELECT EMPLOYEE, EMPLOYER,
STARTDATE, ENDDATE,
REGIONCODE, EID, VALUE, CURRENCY
FROM EMPLOYMENT;
RETURN st_cursor;
END;
To use this query in Hibernate you need to map it via a named query.
<sql-query name = "selectAllEmployees_SP" callable = "true">
<return alias="emp" class="Employment">
<return-property name = "employee" column = "EMPLOYEE"/>
<return-property name = "employer" column = "EMPLOYER"/>
<return-property name = "startDate" column = "STARTDATE"/>
<return-property name = "endDate" column = "ENDDATE"/>
<return-property name = "regionCode" column = "REGIONCODE"/>
<return-property name = "id" column = "EID"/>
<return-property name = "salary">
<return-column name = "VALUE"/>
<return-column name = "CURRENCY"/>
</return-property>
</return>
{ ? = call selectAllEmployments() }
</sql-query>
Stored procedures currently only return scalars and entities.
<return-join>
and <load-collection>
are not supported.
C.4. Legacy rules/limitations for using stored procedures
You cannot use stored procedures with Hibernate unless you follow some procedure/function rules.
If they do not follow those rules they are not usable with Hibernate.
If you still want to use these procedures you have to execute them via session.doWork()
.
The rules are different for each database since database vendors have different stored procedure semantics/syntax.
Stored procedure queries cannot be paged with setFirstResult()/setMaxResults()
.
The recommended call form is standard SQL92: { ? = call functionName(<parameters>) }
or { ? = call procedureName(<parameters>}
.
Native call syntax is not supported.
For Oracle the following rules apply:
-
A function must return a result set.
-
The first parameter of a procedure must be an
OUT
that returns a result set.
This is done by using aSYS_REFCURSOR
type in Oracle 9 or 10.
In Oracle you need to define aREF CURSOR
type.
See Oracle literature for further information.
For Sybase or MS SQL server the following rules apply:
-
The procedure must return a result set.
Note that since these servers can return multiple result sets and update counts, Hibernate will iterate the results and take the first result that is a result set as its return value.
Everything else will be discarded. -
If you can enable
SET NOCOUNT ON
in your procedure it will probably be more efficient, but this is not a requirement.
C.5. Legacy custom SQL for create, update and delete
Hibernate can use custom SQL for create, update, and delete operations.
The SQL can be overridden at the statement level or individual column level.
This section describes statement overrides.
For columns, see Column transformers: read and write expressions.
The following example shows how to define custom SQL operations using annotations.
Example 710. Custom CRUD XML
<class name = "Person">
<id name = "id">
<generator class = "increment"/>
</id>
<property name = "name" not-null = "true"/>
<sql-insert>INSERT INTO PERSON (NAME, ID) VALUES ( UPPER(?), ? )</sql-insert>
<sql-update>UPDATE PERSON SET NAME=UPPER(?) WHERE ID=?</sql-update>
<sql-delete>DELETE FROM PERSON WHERE ID=?</sql-delete>
</class>
If you expect to call a stored procedure, be sure to set the |
To check that the execution happens correctly, Hibernate allows you to define one of those three strategies:
-
none: no check is performed; the store procedure is expected to fail upon issues
-
count: use of rowcount to check that the update is successful
-
param: like COUNT but using an output parameter rather that the standard mechanism
To define the result check style, use the check
parameter which is again available in annotations as well as in xml.
Last but not least, stored procedures are in most cases required to return the number of rows inserted, updated and deleted.
Hibernate always registers the first statement parameter as a numeric output parameter for the CUD operations:
Example 711. Stored procedures and their return value
CREATE OR REPLACE FUNCTION updatePerson (uid IN NUMBER, uname IN VARCHAR2)
RETURN NUMBER IS
BEGIN
update PERSON
set
NAME = uname,
where
ID = uid;
return SQL%ROWCOUNT;
END updatePerson;
C.6. Legacy custom SQL for loading
You can also declare your own SQL (or HQL) queries for entity loading.
As with inserts, updates, and deletes, this can be done at the individual column level as described in
For columns, see Column transformers: read and write expressions or at the statement level.
Here is an example of a statement level override:
<sql-query name = "person">
<return alias = "pers" class = "Person" lock-mode= "upgrade"/>
SELECT NAME AS {pers.name}, ID AS {pers.id}
FROM PERSON
WHERE ID=?
FOR UPDATE
</sql-query>
This is just a named query declaration, as discussed earlier. You can reference this named query in a class mapping:
<class name = "Person">
<id name = "id">
<generator class = "increment"/>
</id>
<property name = "name" not-null = "true"/>
<loader query-ref = "person"/>
</class>
This even works with stored procedures.
You can even define a query for collection loading:
<set name = "employments" inverse = "true">
<key/>
<one-to-many class = "Employment"/>
<loader query-ref = "employments"/>
</set>
<sql-query name = "employments">
<load-collection alias = "emp" role = "Person.employments"/>
SELECT {emp.*}
FROM EMPLOYMENT emp
WHERE EMPLOYER = :id
ORDER BY STARTDATE ASC, EMPLOYEE ASC
</sql-query>
You can also define an entity loader that loads a collection by join fetching:
<sql-query name = "person">
<return alias = "pers" class = "Person"/>
<return-join alias = "emp" property = "pers.employments"/>
SELECT NAME AS {pers.*}, {emp.*}
FROM PERSON pers
LEFT OUTER JOIN EMPLOYMENT emp
ON pers.ID = emp.PERSON_ID
WHERE ID=?
</sql-query>
References
-
[PoEAA] Martin Fowler. Patterns of Enterprise Application Architecture.
Addison-Wesley Professional. 2002. -
[JPwH] Christian Bauer & Gavin King. Java Persistence with Hibernate, Second Edition. Manning Publications Co. 2015.
-
[jdbc] JDBC Specification — Version 4.2
Getting Started Guides per Series
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Содержание
 Предисловие
 1. Доступ к базе данных
  1.1. Подключение
   1.1.1. Конфигурация
   1.1.2. Получение JDBC-соединения
  1.2. Пулинг соединений (Connection pooling)
   1.2.1. Пулинг с помощью с3p0
   1.2.2. Пулинг с помощью Proxool
   1.2.3. Получение соединений от сервера приложений, через JNDI
   1.2.4. Прочее по конфигурации соединений
   1.2.5. Необязательные свойства конфигурации
  1.3. Диалекты
   1.3.1. Указание диалекта для использования
   1.3.2. Разрешение диалекта
  1.4. Автоматическая генерация схемы при помощи Schema Export
   1.4.1. Кастомизация файлов маппинга (Customizing the mapping files)
   1.4.2. Запуск инструмента SchemaExport
Предисловие
Работа как с объектно-ориентированным ПО, так и с реляционными базами данных (далее БД, прим.перев.) может быть весьма обременительной и затратной с точки зрения потраченного времени. Затраты на разработку существенно выше из-за несовпадения парадигм представления данных в объектах и реляционных БД. Hibernate является решением т.н. объектно-реляционного проецирования для Java. Термин объектно-реляционного проецирования отноcится к технике проецирования (маппинга) данных из объектной модели представления к реляционной модели представления (и наоборот). См. en.wikipedia.org/wiki/Object-relational_mapping для более подробного ознакомления.
Hibernate не только заботится о проецировании Java-классов в таблицы БД (а также проецировании базовых типов Java к типам SQL), но и предоставляет механизмы формирования запросов и выборок данных. Он может существенно снизить время на разработку, которая в старом стиле велась путем ручной работы с данными с использованием SQL и JDBC. Главная цель архитектурного дизайна Hibernate – избавление разработчика от ежедневных задач работы с данными БД, путем избавления от нужд написания собственной логики работы с данными через SQL и JDBC. Однако, в отличие от других persistence-решений, Hibernate не скрывает от вас возможность использовать всю мощь SQL, и гарантирует, что ваши вложения в реляционные технологии и знания по-прежнему имеют силу.
Hibernate может быть не лучшим решением для приложений, хранящих всю свою бизнес-логику в хранимых процедурах, оно скорее подходит для объектно-ориентированных моделей и логики в среднем (бизнес) слое приложения, написанном на Java. Однако, Hibernate совершенно точно может помочь вам избавиться или инкапсулировать логику специфического SQL-кода, а также справиться с повседневными задачами трансляции результатов ваших запросов из табличного представления в граф объектов.
1. Доступ к базе данных
1.1. Подключение
Hibernate соединяется с базой от имени вашего приложения. Соединение может осуществляться через различного рода механизмы, а именно:
- Встроенный пул соединений
- javax.sql.DataSource
- Пулы соединений, также можно использовать сторонние открытые решения для пулов:
- c3p0
- proxool
- Собственноручно созданные приложением JDBC-соединения. Это нерекомендуемый подход и единственная причина его использования – работа с устаревшим (legacy) окружением.
Важно
Встроенный пул соединений не предназначен для работы в “боевом” окружении.
Hibernate получает JDBC-соединения по мере необходимости через интерфейс org.hibernate.service.jdbc.connections.spi.ConnectionProvider. Приложения могут также предоставлять свои реализации интерфейса org.hibernate.service.jdbc.connections.spi.ConnectionProvider для определения кастомного подхода к предоставлению соединений Hibernate’у. (Из другого пула соединений, например)
1.1.1. Конфигурация
Вы можете сконфигурировать соединение к базе данных, используя property-файл, через XML-дескриптор развертывания или программно.
Пример 1.1. hibernate.properties для пула соединений c3p0
hibernate.connection.driver_class = org.postgresql.Driver
hibernate.connection.url = jdbc:postgresql://localhost/mydatabase
hibernate.connection.username = myuser
hibernate.connection.password = secret
hibernate.c3p0.min_size=5
hibernate.c3p0.max_size=20
hibernate.c3p0.timeout=1800
hibernate.c3p0.max_statements=50
hibernate.dialect = org.hibernate.dialect.PostgreSQL82Dialect
Пример 1.2. hibernate.cfg.xml для соединения к встраиваемой базе данных HSQL
<?xml version='1.0' encoding='utf-8'?>
<hibernate-configuration
xmlns="http://www.hibernate.org/xsd/hibernate-configuration"
xsi:schemaLocation="http://www.hibernate.org/xsd/hibernate-configuration hibernate-configuration-4.0.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">org.hsqldb.jdbcDriver</property>
<property name="connection.url">jdbc:hsqldb:hsql://localhost</property>
<property name="connection.username">sa</property>
<property name="connection.password"></property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.HSQLDialect</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<mapping resource="org/hibernate/tutorial/domain/Event.hbm.xml"/>
</session-factory>
</hibernate-configuration>
1.1.1.1. Программная конфигурация
Экземпляр объекта org.hibernate.cfg.Configuration представляет полный набор типов маппингов на базу данных. Объект org.hibernate.cfg.Configuration создает иммутабельный объект org.hibernate.SessionFactory, и компилирует маппинги из различных XML-файлов. Вы можете указать файлы для маппинга напрямую, или Hibernate может найти их за вас.
Пример 1.3. Указание файлов для маппинга напрямую
Вы можете получить объект org.hibernate.cfg.Configuration, cоздав его и указав XML-документы для маппинга напрямую. Если файлы для маппинга находятся в classpath, используйте метод addResource().
Configuration cfg = new Configuration()
.addResource("Item.hbm.xml")
.addResource("Bid.hbm.xml");
Пример 1.4. Hibernate находит файлы за вас
Метод addClass() указывает Hibernate искать mapping-файлы через classpath, основываясь на имени класса, при этом избавляя вас от необходимости указывать имена файлов самому. В следующем примере, он ищет org/hibernate/auction/Item.hbm.xml и org/hibernate/auction/Bid.hbm.xml.
Configuration cfg = new Configuration()
.addClass(org.hibernate.auction.Item.class)
.addClass(org.hibernate.auction.Bid.class);
Пример 1.5. Указание свойств конфигурации
Configuration cfg = new Configuration()
.addClass(org.hibernate.auction.Item.class)
.addClass(org.hibernate.auction.Bid.class)
.setProperty("hibernate.dialect", "org.hibernate.dialect.MySQLInnoDBDialect")
.setProperty("hibernate.connection.datasource", "java:comp/env/jdbc/test")
.setProperty("hibernate.order_updates", "true");
Другие способы программной конфигурации Hibernate
- Передача экземпляра java.util.Properties в Configuration.setProperties().
- Установка системного свойства, используя java -Dproperty=value
1.1.2. Получение JDBC-соединения
После того, как вы сконфигурируете Основные jdbc-свойства Hibernate, вы можете использовать метод openSession класса org.hibernate.SessionFactory для открытия сессий. Сессии откроют JDBC-cоединения по требованию, основываясь на предоставленной конфигурации.
Пример 1.6. Открытие сессии
Session session = sessions.openSession();
Основные jdbc-cвойства Hibernate
- hibernate.connection.driver_class
- hibernate.connection.url
- hibernate.connection.username
- hibernate.connection.password
- hibernate.connection.pool_size
1.2. Пулинг соединений (Connection pooling)
Внутренний алгоритм пулинга соединений в Hibernate довольно рудиментарен, и нужен, по большей части, для разработки и тестирования. Используйте сторонние (3rd party) пулы для лучшей производительности и стабильности. Для использования 3rd party пула, замените значение свойства hibernate.connection.pool_size на соответствующие специфике вашего выбранного пула. Это отключит использование встроенного пула Hibernate.
1.2.1. Пулинг с помощью c3p0
C3P0 – опенсорсный пул JDBC-соединений, распространяемый вместе с Hibernate в директории lib/. Hibernate будет использовать свой собственный org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider для пулинга соединений, при настройке свойств hibernate.c3p0.*
Важные конфигурационные свойства для c3p0
- hibernate.c3p0.min_size
- hibernate.c3p0.max_size
- hibernate.c3p0.timeout
- hibernate.c3p0.max_statements
1.2.2. Пулинг с помощью Proxool
Proxool — другой опенсорсный пул, распространяемый вместе с Hibernate в директории lib/. Hibernate будет использовать свой собственный org.hibernate.service.jdbc.connections.internal.ProxoolConnectionProvider для пулинга соединений при соответствующей настройке hibernate.proxool.*. В отличие от c3p0, proxool требует некоторых дополнительных параметров настройки, которые описаны в документации, доступной на proxool.sourceforge.net/configure.html.
Таблица 1.1. Важные конфигурационные свойства для пула соединений Proxool
Свойство | Описание |
---|---|
hibernate.proxool.xml | Сконфигурируйте провайдер Proxool, используя указанный файл XML (.xml добавляется автоматически) |
hibernate.proxool.properties | Сконфигурируйте провайдер Proxool, используя указанный property-файл (.properties добавляется автоматически) |
hibernate.proxool.existing_pool | Конфигурировать ли провайдер Proxool из существующего пула |
hibernate.proxool.pool_alias | Псевдоним пула Proxool. Необходим. |
1.2.3. Получение соединений от сервера приложений, через JNDI
Для использования Hibernate внутри сервера приложений, настройте Hibernate для получения соединений от javax.sql.Datasource, зарегистрированном в JNDI, установив по крайней мере одно из следующих свойств:
Важные свойства для источников данных JNDI
- hibernate.connection.datasource (необходимо)
- hibernate.jndi.url
- hibernate.jndi.class
- hibernate.connection.username
- hibernate.connection.password
JDBC-соединения, полученные из источника данных JNDI, автоматически участвуют в container-managed транзакциях сервера приложений.
1.2.4. Прочее по конфигурации соединений
Вы можете передавать произвольные свойства соединения, добавляя перед ними hibernate.connection. К примеру, для указания свойства charSet используйте имя hibernate.connection.charSet.
Вы можете определить свою стратегию для получения JDBC-соединений, реализовав интерфейс org.hibernate.service.jdbc.connections.spi.ConnectionProvider, и указав вашу пользовательскую реализацию при помощи свойства hibernate.connection.provider_class
1.2.5. Необязательные свойства конфигурации
В дополнение к свойствам, перечисленным выше, Hibernate включает в себя множество других параметров. См. более подробный список на http://docs.jboss.org/hibernate/orm/4.2/devguide/en-US/html_single/.
1.3. Диалекты
Хотя SQL относительно стандартизирован, каждый поставщик СУБД использует свое подмножество поддерживаемых синтаксисов. У этого есть и другой термин, называемый диалектом. Hibernate поддерживает различные вариации диалектов через класс org.hibernate.dialect.Dialect и различные подклассы для каждого vendor-диалекта.
Таблица 1.2. Поддерживаемые диалекты СУБД
1.3.1. Указание диалекта для использования
Разработчик может вручную указать диалект для использования, указав в свойстве hibernate.dialect нужное имя подкласса org.hibernate.dialect.Dialect.
1.3.2. Разрешение диалекта
Заранее предположив, что org.hibernate.service.jdbc.connections.spi.ConnectionProvider был настроен, Hibernate попытается автоматически определить диалект, основываясь на java.sql.DatabaseMetaData получаемым из объекта java.sql.Connection, который в свою очередь достается из org.hibernate.service.jdbc.connections.spi.ConnectionProvider.
Эта функциональность предоставляется экземплярами org.hibernate.service.jdbc.dialect.spi.DialectResolver, зарегистрированными cамим фреймворком. Hibernate идет вместе со стандартным набором распознаваний. Если в вашем приложении требуются дополнительные возможности распознавания диалекта, вполне возможно зарегистрировать кастомную реализацию org.hibernate.service.jdbc.dialect.spi.DialectResolver, как показано ниже
Зарегистрированные реализации org.hibernate.service.jdbc.dialect.spi.DialectResolver добавляются во внутренний список resolverов, так что они имеют приоритет над уже ранее зарегистрированными resolver’ами, а также над стандартными.
1.4. Автоматическая генерация схемы при помощи SchemaExport
SchemaExport – утилита Hibernate, которая генерит DDL-скрипты из ваших файлов маппинга. Сгенерированная схема включает в себя ограничения ссылочной целостности (referential integrity constraints), основные и внешние ключи для сущностей и таблиц коллекций. Она также создает таблицы для последовательностей(sequences) и спроецированных id-генераторов (identity generators).
Важно
Вы должны указать диалект SQL через свойство hibernate.dialect, когда используете эту утилиту, так как DDL сам по себе специфичен для каждого вендора. См подробности в Секции 1.3, “Диалекты”.
Перед тем, как Hibernate сможет сгенерировать вашу схему, вы должны кастомизировать ваши файлы маппинга.
1.4.1. Кастомизация файлов маппинга (Customizing the mapping files)
Hibernate предоставляет ряд элементов и атрибутов для ваших файлов маппинга. Они перечислены в Таблице 1.3, “Элементы и аттрибуты, предоставляемые для кастомизации файлов маппинга”, а логический порядок кастомизации представлен в Процедуре 1.1, “Кастомизация схемы”.
Таблица 1.3. Элементы и атрибуты, предоставляемые для кастомизации файлов маппинга
Имя | Тип значения | Описание |
---|---|---|
length | number | Длина колонки |
precision | number | Десятичная точность колонки |
scale | number | Десятичный масштаб колонки |
not-null | true или false | Может ли колонка содержать null-значения |
unique | true или false | Содержит ли колонка только уникальные значения |
index | string | Имя многоколоночного индекса |
unique-key | string | Имя многоколоночного ограничения на уникальность |
foreign-key | string | Имя ограничения внешнего ключа, генерируемое для ассоциаций. Это относится к <one-to-one>, <many-to-one>, <key>, и <many-to-many> элементам. inverse=«true» пропускаются SchemaExport. |
sql-type | string | Переопределяет тип колонки по-умолчанию. Это относится только к элементу <column>. |
default | string | Значение по-умолчанию для колонки |
check | string | SQL ограничения (SQL check constraint) либо на колонку, либо на таблицу |
Процедура 1.1. Кастомизация схемы
1. Установка длины, точности, и масштаба элементов маппинга.
Множество элементов маппинга определяют необязательные атрибуты, такие как длина, точность, и масштаб.
<property name="zip" length="5"/>
<property name="balance" precision="12" scale="2"/>
2. Установка not-null, UNIQUE, unique-key аттрибутов.
not-null и UNIQUE атрибуты генерируют ограничения на табличные колонки.
Атрибут unique-key группирует колонки в единое ограничение по уникальности. Атрибут переопределяет имя любого сгенерированного ограничения уникальности.
<many-to-one name="bar" column="barId" not-null="true"/>
<element column="serialNumber" type="long" not-null="true" unique="true"/>
<many-to-one name="org" column="orgId" unique-key="OrgEmployeeId"/>
<property name="employeeId" unique-key="OrgEmployee"/>
3. Установка index и foreign-key аттрибутов.
Атрибут index указывает имя индекса для его создания, используя спроецированную колонку или колонки. Вы можете сгруппировать несколько колонок по одному индексу, указав в каждой из них имя одного и того же индекса.
Атрибут внешнего ключа (foreign key) переопределяет имя любого сгенерированного ограничения внешнего ключа.
<many-to-one name="bar" column="barId" foreign-key="FKFooBar"/>
4. Установка дочерних <column>-элементов.
Множество элементов маппинга допускают использование дочерних <column> элементов. Это бывает полезно для маппинга типов, включающих в себя несколько колонок.
<property name="name" type="my.customtypes.Name"/>
<column name="last" not-null="true" index="bar_idx" length="30"/>
<column name="first" not-null="true" index="bar_idx" length="20"/>
<column name="initial"/>
</property>
5. Установка атрибута default.
Атрибут default представляет собой значение по-умолчанию для колонки. Добавьте значение к спроецированному свойству перед сохранением нового экземпляра класса.
<property name="credits" type="integer" insert="false">
<column name="credits" default="10"/>
</property>
<version name="version" type="integer" insert="false">
<column name="version" default="0"/>
</version>
6. Установка атрибута sql-type.
Используйте атрибут sql-type для переопределения маппинга по-умолчанию для типов Java на типы SQL.
<property name="balance" type="float">
<column name="balance" sql-type="decimal(13,3)"/>
</property>
7. Установка атрибута check.
Используйте атрибут check для указания ограничения check.
<property name="foo" type="integer">
<column name="foo" check="foo > 10"/>
</property>
<class name="Foo" table="foos" check="bar < 100.0">
...
<property name="bar" type="float"/>
</class>
8.Добавление <comment> элементов к вашей схеме.
Используйте элемент <comment> для указания комментариев для сгенерированной схемы.
<class name="Customer" table="CurCust">
<comment>Current customers only</comment>
...
</class>
1.4.2. Запуск инструмента SchemaExport
Инструмент SchemaExport записывает DDL-скрипт в стандартный поток вывода, исполняет DDL, или и то, и другое сразу.
Пример 1.7. Синтаксис SchemaExport
java -cp hibernate_classpaths org.hibernate.tool.hbm2ddl.SchemaExport options mapping_files
Таблица 1.4. Опции SchemaExport
Опция | Описание |
---|---|
—quiet | Не выводить скрипт в стандартный поток вывода |
—drop | Только удалять таблицы |
—create | Только создавать таблицы |
—text | Не экспортировать в БД |
—output=my_schema.ddl | Вывести скрипт в указанный файл |
—naming=eg.MyNamingStrategy | выбор NamingStrategy |
—namingdelegator=eg.MyNamingStrategyDelegator | выбор NamingStrategyDelegator |
—config=hibernate.cfg.xml | Чтение конфигурации Hibernate из файла XML |
—properties=hibernate.properties | Чтение свойств БД из указанного файла |
—format | Опрятное форматирование SQL |
—delimiter=; | Разделитель строк |
Важно
Опции —naming и —namingdelegator, не должны использоваться вместе
Пример 1.8. Встраивание SchemaExport в ваше приложение
Configuration cfg = ....;
new SchemaExport(cfg).create(false, true);
Hibernate is the most used Object/Relational persistence and query service and It is licensed under the open-source GNU Lesser General Public License (LGPL). Hibernate not only see the mapping from Java classes to database tables but also provides data query and recovery facilities. Hibernate is free to download.
This Hibernate Tutorial is designed for beginners and experienced professionals, which helps you to use Hibernate to create database-based web applications in simple and easy steps and learn fundamental and advanced concepts of Hibernate including setting up Hibernate, mapping Java classes to database tables, performing basic and advanced database operations, utilizing Hibernate Query Language (HQL), and more.
What is Hibernate Framework?
Hibernate is a Java framework, licensed under the open-source GNU Lesser General Public License (LGPL), and is available for free download. Developed in 2001 by Gavin King, Hibernate was introduced as a groundbreaking alternative to the EJB2-style entity bean approach. By mapping Java objects to database tables, it streamlines data persistence and retrieval without the need for complex SQL queries. With features like automatic transaction management and caching, Hibernate simplifies and optimizes database interactions, making it an indispensable framework for efficient data management in Java applications.
What is JDBC?
JDBC (Java Database Connectivity) provides a set of Java APIs to access the relational databases from the Java program. Java APIs enable programs to execute SQL statements and interact with any SQL database.
JDBC gives a flexible architecture to write a database-independent web application that can execute on different platforms and interact with different DBMS without any change.
ORM Tool
An ORM tool simplifies the data creation, data manipulation and data access and It is a programming technique that maps the object to the data stored in the database.
ORM Tool
The ORM tool internally uses the JDBC API to interact with the database.
What is JPA?
- Java Persistence API (JPA) is a Java specification that provides specific functionality and is a standard for ORM tools.
- javax.persistence package contains the JPA classes and interfaces.
Hibernate Tutorial Index |
---|
Basic |
Core Hibernate |
Hibernate Mapping |
Hibernate Annotations |
Hibernate with Spring Framework |
Hibernate with Database |
Hibernate Log4j |
Inheritance Mapping |
Hibernate Basics
- Introduction to Hibernate Framework
- Hibernate Architecture
- Hibernate Lifecycle
- Difference between JDBC and Hibernate in Java
- JPA vs Hibernate
- Hibernate – Difference Between ORM and JDBC
- Hibernate Example using XML in Eclipse
- Hibernate – Create Hibernate Configuration File with the Help of Plugin
Core Hibernate
- Hibernate – Cache Eviction with Example
- Hibernate – Cache Expiration
- Hibernate – Enable and Implement First and Second Level Cache
- Hibernate – Pagination
- Hibernate – Different Cascade Types
- Hibernate – Caching
- Hibernate – Eager/Lazy Loading
- Hibernate – get() and load() Method
- Hibernate Validator with Example
- Hibernate – Batch Processing
- Hibernate – Interceptors
- Hibernate – Criteria Queries
- Hibernate – Create POJO Classes
- Hibernate – Web Application
- Hibernate – Generator Classes
- Hibernate Example without IDE
Hibernate Mapping
- Hibernate – One-to-One Mapping
- Hibernate – One-to-Many Mapping
- Hibernate – Many-to-One Mapping
- Hibernate – Many-to-Many Mapping
- Hibernate – Component Mapping
- Hibernate – Mapping List
- Hibernate – Collection Mapping
- Hibernate – Bag Mapping
- Hibernate – Difference Between List and Bag Mapping
- Hibernate – SortedSet Mapping
- Hibernate – SortedMap Mapping
- Hibernate – Bidirectional Association
- Hibernate – Lazy Collection
Hibernate Annotations
- Hibernate – Annotations
- Hibernate – @Embeddable and @Embedded Annotation
Hibernate JPA Annotations:
- @Entity
- @Table
- @Column
- @Id
- @GeneratedValue
- @Version
- @OrderBy
- @Transient
- @Lob
Hibernate Association Mapping Annotations:
- @OneToOne
- @ManyToOne
- @OneToMany
- @ManyToMany
- @PrimaryKeyJoinColumn
- @JoinColumn
- @MapsId
Hibernate with Spring Framework
- Spring Hibernate Configuration and Create a Table in Database
- Spring ORM Example using Hibernate
- Spring Boot – Validation using Hibernate Validator
- How to Create a Project using Spring MVC and Hibernate 5?
- Spring Boot – Integrating Hibernate and JPA
Hibernate with Database
- Hibernate – Save Image and Other Types of Values to Database
- Hibernate Native SQL Query with Example
- CRUD Operations using Hibernate
- Automatic Table Creation Using Hibernate
- Hibernate – Native SQL
- Hibernate – SQL Dialects
- Hibernate – Query Language
- Hibernate Example using JPA and MySQL
Hibernate Log4j
- Hibernate – Logging by Log4j using xml File
- Hibernate – Logging By Log4j Using Properties File
Inheritance Mapping
- Hibernate – Inheritance Mapping
- Hibernate – Table Per Hierarchy using XML File
- Hibernate – Table Per Hierarchy using Annotation
- Hibernate – Table Per Concrete Class using XML File
- Hibernate – Table Per Concrete Class Using Annotation
- Hibernate – Table Per Subclass Example using XML File
- Hibernate – Table Per Subclass using Annotation
Hibernate Inheritance Mapping Annotations:
- @Inheritance
- @DiscriminatorColumn
- @DiscriminatorValue
Hibernate Advantages
Here are the advantages of Hibernate:
- Hibernate map Java classes to database tables using XML files.
- It provides APIs for storing and retrieving Java objects directly from the database.
- If there is a change in the database, then we just need to change the XML file properties.
- Abstracts out the unknown SQL types and provides a way to work around standard Java Objects.
- It does not require an application server to operate.
- Manipulates Complex relationships of objects in the database.
- Minimizes database access with smart fetching strategies.
- Simple querying of data.
Hibernate Supported Databases
Hibernate supports almost all the major RDBMS. Following is a list of a few of the database engines that are supported by Hibernate −
- HSQL Database Engine
- DB2/NT
- MySQL
- PostgreSQL
- FrontBase
- Oracle
- Microsoft SQL Server Database
- Sybase SQL Server
- Informix Dynamic Server
Hibernate Tutorial – FAQs
1. What is Hibernate and why it is used?
Hibernate is a Java framework used for simplifying database operations by mapping Java objects to relational database tables.
2. What is the basics of Hibernate?
The basics of Hibernate involve defining mappings between Java classes and database tables, allowing seamless interaction between the two and It abstracts away the complexities of database operations, making it easier to work with databases in Java applications.
3. Is Hibernate easy to learn?
Hibernate can be challenging for beginners, but with practice, it becomes easier to learn. A good understanding of Java and basic database concepts is helpful.
4. What is the difference between JDBC and Hibernate?
The main difference between JDBC and Hibernate is that JDBC is a low-level API that requires manual handling of database connections, writing SQL queries, and managing result sets and Hibernate, on the other hand, is a higher-level ORM framework that automates these tasks, allowing developers to work with Java objects and abstracting away the low-level database operations.
Last Updated :
24 Jul, 2023
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1.1. Часть 1 — Первое приложение Hibernate
- 1.1.1. Установка
- 1.1.2. Первый класс
- 1.1.3. Файл отображений
- 1.1.4. Конфигурирование Hibernate
- 1.1.5. Сборка с Maven
- 1.1.6. Запуск и помошники
- 1.1.7. Загрузка и хранение объектов
-
1.2. Часть 2 — Отображение ассоциаций
- 1.2.1. Отображение для класса Person
- 1.2.2. Однонаправленная ассоциация на основе Set
- 1.2.3. Работа с ассоциациями
- 1.2.4. Коллекия значений
- 1.2.5. Двунаправленные ассоциации
- 1.2.6. Работа двунаправленных связей
-
1.3. Часть 3 — приложение Менеджер событий
- 1.3.1. Написание основного сервлета
- 1.3.2. Обработка и визуализация
- 1.3.3. Развёртывание и тестирование
- 1.4. Резюме
Предназначенная для новых пользователей, эта глава содержит пошаговое введение в Hibernate,
начиная с простого приложения, используя базу данных в памяти (in-memory).
Учебник основан на более раннем учебнике, разработанном Майклом Глоэлем.
Весь код содержится в tutorials/web
источника проекта.
Важно
В этом учебнике предполагается, что пользователь знает как Java, так и SQL.
Если у вас есть ограниченное знание JAVA или SQL, рекомендуется начать
с хорошего ознакомления с этой технологией, прежде чем пытаться изучить Hibernate.
Заметка
Дистрибутив содержит другое приложение-пример в директории tutorial/eg
1.1. Часть 1 — Первое приложение Hibernate
В этом примере мы создадим небольшое приложение базы данных, которое может хранить события,
которые мы хотим посетить, и информацию о хостах(hosts) этих событий.
Заметка
Несмотря на то, что вы можете использовать любую базу данных,
с которой вам удобно пользоваться, мы будем использовать
HSQLDB (базу данных в памяти,
базу данных Java), чтобы избежать описания установки/настройки каких-либо конкретных серверов баз данных.
1.1.1. Установка
Первое, что нам нужно сделать, это настроить среду разработки. Мы будем использовать
«стандартную компоновку», которую пропагандируют многие инструменты сборки,
такие как Maven. У Maven, в частности,
есть хороший ресурс, описывающий этот
макет.
Поскольку этот учебник должен быть веб-приложением, мы будем создавать и использовать каталоги
src/main/java, src/main/resources
и src/main webapp
.
Мы будем использовать Maven в этом учебном пособии, используя возможности
его транзитивных функций управления зависимостями, а также способность многих IDE
автоматически настраивать проект для нас на основе дескриптора maven.
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.hibernate.tutorials</groupId> <artifactId>hibernate-tutorial</artifactId> <version>1.0.0-SNAPSHOT</version> <name>First Hibernate Tutorial</name> <build> <!-- we dont want the version to be part of the generated war file name --> <finalName>${artifactId}</finalName> </build> <dependencies> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-core</artifactId> </dependency> <!-- Because this is a web app, we also have a dependency on the servlet api. --> <dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> </dependency> <!-- Hibernate uses slf4j for logging, for our purposes here use the simple backend --> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-simple</artifactId> </dependency> <dependency> <groupId>javassist</groupId> <artifactId>javassist</artifactId> </dependency> </dependencies> </project>
Совет
Это не требование использовать Maven. Если вы хотите использовать что-то еще
для сборки проекта (например, Ant), макет останется прежним.
Единственное изменение заключается в том, что вам нужно будет вручную добавить
все необходимые зависимости. Если вы используете что-то вроде Ivy,
обеспечивающее транзитивное управление зависимостями, вы все равно будете добавлять зависимости,
упомянутые ниже. В противном случае вам нужно будет указать все зависимости,
как явные, так и транзитивные, добавив их в путь к классу проекта.
Если вы работаете из дистрибутива Hibernate, это будет означать hibernate3.jar,
все артефакты в каталоге lib/required
и все файлы из каталога
lib/bytecode/cglib
или lib/bytecode/javassist
кроме того,
вам понадобятся как servlet-api jar, так и один из бэкэндов регистрации slf4j.
Сохраните этот файл как pom.xml
в корневом каталоге проекта.
1.1.2. Первый класс
package org.hibernate.tutorial.domain;
import java.util.Date;
public class Event { private Long id; private String title; private Date date;
public Event() { }
public Long getId() { return id; }
private void setId(Long id) { this.id = id; }
public Date getDate() { return date; }
public void setDate(Date date) { this.date = date; }
public String getTitle() { return title; }
public void setTitle(String title) { this.title = title; } }
Этот класс использует стандартные соглашения JavaBean об именах методов getter и setter для полей,
а также конфиденциальную видимость полей. Хотя это рекомендуемый дизайн, он не требуется.
Hibernate также может напрямую обращаться к полям,
преимущество методов доступа — это надежность для рефакторинга.
Свойство id содержит уникальное значение идентификатора для определенного события.
Все постоянные классы сущностей (также как и менее важные зависимые классы) нуждаются в таком идентификаторе,
если мы хотим использовать полный набор функций Hibernate. Фактически, большинство приложений,
особенно веб-приложений, должны различать объекты по идентификатору, поэтому вы должны
рассматривать это как особенность, а не как ограничение. Однако мы обычно
не манипулируем идентификацией объекта, поэтому метод setter должен быть закрытым.
Только Hibernate присваивает идентификаторы при сохранении объекта. Hibernate может напрямую обращаться
к общедоступным, приватным и защищенным методам доступа, а также к открытым,
закрытым и защищенным полям. Выбор зависит от вас, и вы можете соответствовать
ему в соответствии с дизайном вашего приложения.
Конструктор без аргументов является обязательным требованием для всех постоянных (persistent) классов;
Hibernate должен создавать объекты для вас, используя Java Reflection. Конструктор может быть закрытым,
однако для генерации прокси-сервера во время выполнения и эффективного извлечения данных
без инструментария байт-кода требуется пакетная (package) или общедоступная (public) видимость.
Смотри этот файл в директории src/main/java/org/hibernate/tutorial/domain
1.1.3. Файл отображений (mapping)
Hibernate должен знать, как загружать и хранить объекты постоянного (persistent) класса.
Здесь вступает в игру файл отображения (mapping) Hibernate. Файл отображения сообщает Hibernate,
какую таблицу в базе данных он должен получить, и какие столбцы в этой таблице
он должен использовать.
Основная структура файла отображения выглядит так:
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="org.hibernate.tutorial.domain"> [...] </hibernate-mapping>
Hibernate DTD сложный. Вы можете использовать его для автоматического завершения элементов
и атрибутов XML-отображения в вашем редакторе или в среде IDE. Открытие DTD-файла
в текстовом редакторе — это самый простой способ получить обзор всех элементов
и атрибутов, а также просмотреть значения по умолчанию, а также некоторые комментарии.
Hibernate не будет загружать DTD-файл из Интернета, но сначала просмотрите его из пути
к классам приложения. Файл DTD включён в hibernate-core.jar (он также включён
в hibernate3.jar, если используется дистрибутивный пакет).
Важно
Мы опустим декларацию DTD в будущих примерах, чтобы сократить код.
Между двумя тегами hibernate-mapping
включают элемент class
.
Все постоянные (persistent) классы сущностей (опять же, впоследствии могут быть зависимые классы,
которые не являются первоклассными сущностями) необходимо отображение с таблицей
в базе данных SQL:
<hibernate-mapping package="org.hibernate.tutorial.domain"> <class name="Event" table="EVENTS">
</class> </hibernate-mapping>
До сих пор мы говорили Hibernate, как сохранять и загружать объект класса
Event
в таблицу EVENTS
. Каждый экземпляр теперь представлен строкой
в этой таблице. Теперь мы можем продолжить, отображая свойство уникального идентификатора
на первичный ключ таблиц. Поскольку мы не хотим заботиться об обработке этого
идентификатора, мы настраиваем стратегию генерации идентификатора Hibernate для суррогатного
столбца первичного ключа:
<hibernate-mapping package="org.hibernate.tutorial.domain"> <class name="Event" table="EVENTS"> <id name="id" column="EVENT_ID"> <generator class="native" /> </id> </class> </hibernate-mapping>
Элемент id
является объявлением свойства идентификатора. Атрибут отображения
name="id"
объявляет имя свойства JavaBean и сообщает Hibernate использовать методы
getId()
и setId()
для доступа к свойству. Атрибут column
указывает Hibernate, в каком столбце таблицы EVENTS
хранится значение первичного ключа.
Вложенный элемент generator
определяет стратегию генерации идентификатора (также как генерируются
значения идентификатора?). В этом случае мы выбираем native
,
который предлагает уровень переносимости в зависимости от настроенного диалекта базы данных.
Hibernate поддерживает идентификаторы, создаваемые базой данных, глобально уникальные,
а также назначенные приложением. Генерация значения идентификатора также является одной
из многих точек расширения Hibernate, и вы можете подключиться к своей собственной стратегии.
Наконец, нам нужно сообщить Hibernate об остальных свойствах класса объектов. По умолчанию
свойства класса не считаются постоянными (persistent):
<hibernate-mapping package="org.hibernate.tutorial.domain"> <class name="Event" table="EVENTS"> <id name="id" column="EVENT_ID"> <generator class="native" /> </id> <property name="date" type="timestamp" column="EVENT_DATE" /> <property name="title" /> </class> </hibernate-mapping>
Подобно элементу id
, атрибут name
элемента свойства сообщает Hibernate,
какие методы getter и setter использовать. В этом случае Hibernate будет искать методы
getDate(), setDate(), getTitle()
и setTitle()
.
Заметка
Почему отображение свойства date
включает атрибут column
,
но title
не указан? Без атрибута column
Hibernate
по умолчанию использует имя свойства как имя столбца. Это работает для title
,
однако date
является зарезервированным ключевым словом в большинстве баз данных,
поэтому вам нужно будет отобразать ее с другим именем.
В title
также отсутствует атрибут type
. Типы, объявленные
и используемые в файлах отображений, не являются типами данных Java;
они также не являются типами баз данных SQL. Эти типы называются
типами отображения Hibernate (Hibernate mapping types), которые могут переводить
типы данных Java в SQL и наоборот. Опять же, Hibernate попытается определить
правильный тип преобразования и отображения, если атрибут type
отсутствует в отображении.
В некоторых случаях это автоматическое обнаружение с использованием Reflection на Java-классе
может не иметь значения по умолчанию, которое вы ожидаете.
Это относится к свойству date
. Hibernate не может знать, должно ли свойство
java.util.Date
отображаться на SQL date, timestamp
или time
.
Полная информация о дате и времени сохраняется путем отображения свойства с преобразователем
временной метки.
Совет
Hibernate определяет типа отображения, используя отражение при обработке файлов отображения.
Это может занять много времени и ресурсов, поэтому, если производительность важна,
вам следует рассмотреть явное определение используемого типа.
Сохраните файл отображения как src/main/resources/org/hibernate/tutorial/domain/Event.hbm.xml.
1.1.4. Конфигурирование Hibernate
На этом этапе у вас должен быть постоянный (persistent) класс и его файл отображения.
Настало время настроить Hibernate. Сначала давайте настроим HSQLDB для запуска в «режиме сервера».
Заметка
Мы делаем это так, чтобы данные оставались между запусками.
Мы будем использовать плагин Maven exec для запуска сервера HSQLDB, выполнив:
mvn exec: java -Dexec.mainClass=»org.hsqldb.Server» -Dexec.args=»- database.0 file: target/data/tutorial»
Вы увидите, что он запускается и привязывается к сокету TCP/IP.
Здесь наше приложение будет подключаться позже. Если вы хотите начать с новой базой данных,
выключите HSQLDB, удалите все файлы в каталоге target/data и снова запустите HSQLDB.
Hibernate будет подключаться к базе данных от имени вашего приложения, поэтому он должен знать,
как получить соединения. Для этого урока мы будем использовать автономный пул соединений
(в отличие от javax.sql.DataSource
). Hibernate поставляется с поддержкой двух
сторонних пулов соединений JDBC с открытым исходным кодом:
c3p0
и proxool.
Однако для этого учебника мы будем использовать встроенный пул соединений Hibernate.
Осторожно
Встроенный пул соединений Hibernate никоим образом не предназначен для использования
в продакшене. Он не имеет нескольких функций, имеющихся в любом приличном пуле подключений.
Для конфигурации Hibernate мы можем использовать простой файл hibernate.properties
,
более сложный файл hibernate.cfg.xml
или даже полную программную настройку.
Большинство пользователей предпочитают файл конфигурации XML:
<?xml version='1.0' encoding='utf-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <!-- Database connection settings --> <property name="connection.driver_class">org.hsqldb.jdbcDriver</property> <property name="connection.url">jdbc:hsqldb:hsql://localhost</property> <property name="connection.username">sa</property> <property name="connection.password"></property>
<!-- JDBC connection pool (use the built-in) --> <property name="connection.pool_size">1</property>
<!-- SQL dialect --> <property name="dialect">org.hibernate.dialect.HSQLDialect</property>
<!-- Enable Hibernate's automatic session context management --> <property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache --> <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout --> <property name="show_sql">true</property>
<!-- Drop and re-create the database schema on startup --> <property name="hbm2ddl.auto">update</property>
<mapping resource="org/hibernate/tutorial/domain/Event.hbm.xml"/> </session-factory> </hibernate-configuration>
Заметка
Обратите внимание, что этот файл конфигурации указывает другой DTD
Вы настраиваете SessionFactory
для Hibernate. SessionFactory является глобальной фабрикой,
ответственной за конкретную базу данных. Если у вас несколько баз данных, для упрощения запуска
вы должны использовать несколько конфигураций <session-factory>
в нескольких файлах конфигурации.
Первые четыре элемента свойств содержат необходимую конфигурацию для соединения JDBC.
Элемент свойства dialect указывает конкретный вариант SQL, генерируемый Hibernate.
В этом контексте особенно полезно автоматическое управление сессией Hibernate для контекстов
персистентности. Опция hbm2ddl.auto
включает автоматическую генерацию схем баз данных
непосредственно в базу данных. Это также можно отключить, удалив параметр конфигурации или перенаправив
его в файл с помощью задачи SchemaExport
в Ant. Наконец, добавьте файлы отображений
для постоянных (persistent) классов в конфигурацию.
Сохрание файл hibernate.cfg.xml
в директорию src/main/resources
.
1.1.5. Сборка с Maven
Теперь мы построим учебный пример с Maven. Вам нужно будет установить Maven;
он доступен на странице загрузки Maven.
Maven будет читать файл /pom.xml
, который мы создали ранее, и узнает,
как выполнять некоторые основные задачи проекта. Во-первых, давайте запустим цель компиляции, чтобы убедиться,
что мы все можем скомпилировать:
[hibernateTutorial]$ mvn compile [INFO] Scanning for projects... [INFO] ------------------------------------------------------------------------ [INFO] Building First Hibernate Tutorial [INFO] task-segment: [compile] [INFO] ------------------------------------------------------------------------ [INFO] [resources:resources] [INFO] Using default encoding to copy filtered resources. [INFO] [compiler:compile] [INFO] Compiling 1 source file to /home/steve/projects/sandbox/hibernateTutorial/target/classes [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESSFUL [INFO] ------------------------------------------------------------------------ [INFO] Total time: 2 seconds [INFO] Finished at: Tue Jun 09 12:25:25 CDT 2009 [INFO] Final Memory: 5M/547M [INFO] ------------------------------------------------------------------------
1.1.6. Запуск и помошники
Настало время загрузить и сохранить некоторые объекты Event
, но сначала
вы должны завершить настройку с помощью некоторого кода инфраструктуры. Вам нужно запустить Hibernate,
создав глобальный объект org.hibernate.SessionFactory
и сохранив его где-нибудь
для легкого доступа в коде приложения. Для получения экземпляров org.hibernate.Session
используется org.hibernate.SessionFactory
. org.hibernate.Session
представляет
собой однопоточную единицу работы. org.hibernate.SessionFactory
— это потокобезопасный
глобальный объект, созданный один раз.
Мы создадим вспомогательный класс HibernateUtil
, который позаботится о запуске
и сделает доступ к org.hibernate.SessionFactory
более удобным.
package org.hibernate.tutorial.util;
import org.hibernate.SessionFactory; import org.hibernate.boot.registry.StandardServiceRegistryBuilder; import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();
private static SessionFactory buildSessionFactory() { try { // Создать SessionFactory из hibernate.cfg.xml return new Configuration().configure().buildSessionFactory( new StandardServiceRegistryBuilder().build() ); } catch (Throwable ex) { // Убедиться что исключения логируются, поскольку они могут быть потеряны System.err.println("Initial SessionFactory creation failed." + ex); throw new ExceptionInInitializerError(ex); } }
public static SessionFactory getSessionFactory() { return sessionFactory; } }
Сохрание код в src/main/java/org/hibernate/tutorial/util/HibernateUtil.java
Этот класс не только создает глобальную ссылку org.hibernate.SessionFactory
в своем статическом инициализаторе; он также скрывает тот факт, что он использует
статический синглтон. Мы могли бы также найти ссылку org.hibernate.SessionFactory
из JNDI на сервере приложений или в любом другом месте, если на то пошло.
Если вы укажете имя org.hibernate.SessionFactory
в вашей конфигурации,
Hibernate попытается связать его с JNDI под этим именем после его создания. Другой, лучший
вариант — использовать развертывание JMX и позволить контейнеру, совместимому с JMX,
создавать экземпляр и связывать HibernateService
с JNDI.
Такие расширенные варианты обсуждаются далее.
Теперь вам нужно настроить систему ведения журнала. Hibernate предоставляет логирование в двух вариантах:
log4j и JDK 1.4 logging. Большинство разработчиков предпочитают Log4j: скопируйте
log4j.properties
из каталога etc/ дистрибутива Hibernate в каталог src,
рядом с hibernate.cfg.xml
. Если вы предпочитаете иметь более подробный вывод,
чем тот, который приведен в примере конфигурации, вы можете изменить настройки.
По умолчанию в стандартный поток вывода (stdout) отображается только сообщение о запуске Hibernate.
Инфраструктура учебного проекта создана, и теперь вы готовы к реальной работе с Hibernate.
1.1.7. Загрузка и хранение объектов
Теперь мы готовы начать настоящую работу с Hibernate. Давайте начнем написание класса
EventManager
с метода main():
package org.hibernate.tutorial;
import org.hibernate.Session; import java.util.*; import org.hibernate.tutorial.domain.Event; import org.hibernate.tutorial.util.HibernateUtil;
public class EventManager {
public static void main(String[] args) { EventManager mgr = new EventManager(); if (args[0].equals("store")) { mgr.createAndStoreEvent("My Event", new Date()); } HibernateUtil.getSessionFactory().close(); }
private void createAndStoreEvent(String title, Date theDate) { Session session = HibernateUtil.getSessionFactory().getCurrentSession(); session.beginTransaction(); Event theEvent = new Event(); theEvent.setTitle(title); theEvent.setDate(theDate); session.save(theEvent); session.getTransaction().commit(); } }
В createAndStoreEvent() мы создали новый объект Event
и передали его в Hibernate.
В этот момент Hibernate позаботится о SQL и выполнит INSERT в базе данных.
Организация org.hibernate.Session
предназначена для представления единой единицы работы
(единый неделимый кусок, который необходимо выполнить). На данный момент мы будем держать
вещи простыми и предполагать индивидуальную детализацию между Hibernate org.hibernate.Session
и транзакцией базы данных. Чтобы защитить наш код от реальной базовой системы транзакций,
мы используем API-интерфейс Hibernate org.hibernate.Transaction
. В этом конкретном
случае мы используем транзакционную семантику на основе JDBC, но она также может работать с JTA.
Что делает sessionFactory.getCurrentSession()
? Во-первых, вы можете вызывать его много раз
и в любом месте, которое вам нравится, когда у вас будет
экземпляр org.hibernate.SessionFactory
. Метод getCurrentSession()
всегда
возвращает «текущую» единицу работы. Помните, что мы переключили параметр конфигурации
для этого механизма на «thread» в нашем src/main/resources/hibernate.cfg.xml
?
Из-за этого параметра контекст текущей единицы работы привязан к текущему потоку Java,
который выполняет приложение.
Важно
Hibernate предлагает три метода отслеживания текущей сессии. Метод, основанный на потоке
(«thread»), не предназначен для использования в продакшене; это просто полезно
для прототипов и учебных приложений, такого как это. Текущее («current») отслеживание
сессии обсуждается более подробно далее.
org.hibernate.Session
начинается, когда первый вызов getCurrentSession()
выполняется для текущего потока. Он привязывает Hibernate к текущему потоку. Когда транзакция
заканчивается, либо путем фиксации (commit), либо отката (rollback), Hibernate автоматически отвязывает
org.hibernate.Session
от потока и закрывает его за вас. Если вы снова вызове
getCurrentSession()
, вы получите новый org.hibernate.Session
и сможете
начать новую единицу работы.
В зависимости от объема единицы работы, должен ли Hibernate org.hibernate.Session
использоваться для выполнения одной или нескольких операций с базой данных? В приведенном
выше примере используется один org.hibernate.Session
для одной операции. Однако это чистое
совпадение; пример просто недостаточно сложный, чтобы показать какой-либо другой подход. Объем
Hibernate org.hibernate.Session
является гибким, но вы никогда не должны
проектировать ваше приложение для использования нового Hibernate org.hibernate.Session
для каждой операции с базой данных. Несмотря на то, что он используется в следующих
примерах, рассматривайте сессионную операцию (session-per-operation) как анти-шаблон.
Настоящее веб-приложение, показаное далее в этом учебнике, поможет проиллюстрировать это.
Дополнительную информацию об обработке транзакций см. в
главе 13 «Транзакции и параллельное исполнение». Предыдущий пример
также пропустил обработку ошибок и откат (rollback).
Чтобы запустить пример, мы будем использовать плагин Maven exec для вызова нашего класса
с необходимой установкой пути к классам:
mvn exec: java -Dexec.mainClass=»org.hibernate.tutorial.EventManager» -Dexec.args=»store»
Заметка
Возможно, вам придется сначала выполнить mvn compile.
Вы должны увидеть запуск Hibernate и, в зависимости от вашей конфигурации,
много выходных данных журнала. К концу будет отображаться следующая строка:
[java] Hibernate: insert into EVENTS (EVENT_DATE, title, EVENT_ID) values (?, ?, ?)
Это INSERT, выполненный Hibernate.
Чтобы перечислить сохраненные события, к основному методу добавляется опция:
if (args[0].equals("store")) { mgr.createAndStoreEvent("My Event", new Date()); } else if (args[0].equals("list")) { List events = mgr.listEvents(); for (int i = 0; i < events.size(); i++) { Event theEvent = (Event) events.get(i); System.out.println( "Event: " + theEvent.getTitle() + " Time: " + theEvent.getDate() ); } }
Также добавлен новый метод listEvents()
:
private List listEvents() { Session session = HibernateUtil.getSessionFactory().getCurrentSession(); session.beginTransaction(); List result = session.createQuery("from Event").list(); session.getTransaction().commit(); return result; }
Здесь мы используем запрос Hibernate Query Language (HQL) для загрузки всех существующих объектов
Event
из базы данных. Hibernate сгенерирует соответствующий SQL, отправит его
в базу данных и заполнит объекты Event
данными. Вы можете создавать более сложные
запросы с помощью HQL. Дополнительную информацию см.
в главе 16, HQL: язык запросов Hibernate.
Теперь мы можем назвать нашу новую функциональность, снова используя плагин Maven exec:
mvn exec: java -Dexec.mainClass=»org.hibernate.tutorial.EventManager» -Dexec.args=»list»
1.2. Часть 2 — Отображение ассоциаций
До сих пор мы отображали один постоянный (persistent) класс сущностей с изолированной таблицей.
Давайте немного расширим пример и добавим ещё несколько классов и ассоциации. Мы добавим людей
в приложение и сохраним список событий, в которых они участвуют.
1.2.1. Отображение для класса Person
Первый набросок класса Person
выглядит следующим образом:
package org.hibernate.tutorial.domain;
public class Person {
private Long id; private int age; private String firstname; private String lastname;
public Person() { ... }
// Accessor methods for all properties, private setter for 'id' }
Сохраните код в файл с именем src/main/java/org/hibernate/tutorial/domain/Person.java
Далее, создайте новый файл отображения src/main/resources/org/hibernate/tutorial/domain/Person.hbm.xml
<hibernate-mapping package="org.hibernate.tutorial.domain">
<class name="Person" table="PERSON"> <id name="id" column="PERSON_ID"> <generator class="native"/> </id> <property name="age"/> <property name="firstname"/> <property name="lastname"/> </class>
</hibernate-mapping>
Добавьте новый файл отображения в конфигурацию Hibernate:
<mapping resource="org/hibernate/tutorial/domain/Event.hbm.xml"/> <mapping resource="org/hibernate/tutorial/domain/Person.hbm.xml"/>
Создайте связь между этими двумя объектами. Люди могут участвовать в мероприятиях,
а у событий — есть участники. Вопросы дизайна, с которыми вам приходится иметь дело:
— это направленность, множественность и поведение коллекции.
1.2.2. Однонаправленная ассоциация на основе Set
Добавляя коллекцию событий в класс Person, вы можете легко перейти к событиям для определенного
человека, не выполняя явный запрос — вызывая Person#getEvents
.
Многозначные ассоциации представлены в Hibernate одним из контрактов Java Collection Framework;
здесь мы выбираем java.util.Set
, потому что коллекция не будет содержать повторяющиеся
элементы, а порядок не имеет отношения к нашим примерам:
public class Person {
private Set events = new HashSet();
public Set getEvents() { return events; }
public void setEvents(Set events) { this.events = events; } }
Перед отображением этой ассоциации рассмотрим другой случай. Мы могли бы просто сохранить
её как однонаправленную или создать еще одну коллекцию в Event
, если бы мы хотели,
чтобы была связь в обоих направлениях. Это необязательно с функциональной точки зрения.
Вы всегда можете выполнить явный запрос для извлечения участников для определенного события.
Этот выбор в дизайне оставлен вам, но то, что ясно из этого обсуждения, —
это множественность ассоциации: «many», указанное в обеих ассоциациях, называется ассоциацией
«многие-ко-многим» (many-to-many). Следовательно, мы используем отображение Hibernate
many-to-many:
<class name="Person" table="PERSON"> <id name="id" column="PERSON_ID"> <generator class="native"/> </id> <property name="age"/> <property name="firstname"/> <property name="lastname"/>
<set name="events" table="PERSON_EVENT"> <key column="PERSON_ID"/> <many-to-many column="EVENT_ID" class="Event"/> </set> </class>
Hibernate поддерживает широкий спектр коллекционных отображений, наиболее часто встречается Set
.
Для ассоциации «многие-ко-многим» или отношения сущности n:m требуется таблица ассоциации.
Каждая строка в этой таблице представляет собой связь между человеком и событием.
Имя таблицы объявляется с использованием атрибута table
заданного элемента.
Имя столбца идентификатора в ассоциации для стороны пользователя определяется ключевым элементом,
именем столбца для стороны события с атрибутом column
для многих-ко-многим
.
Вы также должны указать Hibernate класс объектов в вашей коллекции (класс на другой стороне
коллекции ссылок).
Таким образом, схема базы данных для этого отображения:
_____________ __________________ | | | | _____________ | EVENTS | | PERSON_EVENT | | | |_____________| |__________________| | PERSON | | | | | |_____________| | *EVENT_ID | <--> | *EVENT_ID | | | | EVENT_DATE | | *PERSON_ID | <--> | *PERSON_ID | | TITLE | |__________________| | AGE | |_____________| | FIRSTNAME | | LASTNAME | |_____________|
1.2.3. Работа с ассоциациями
Теперь мы добавим несколько людей и событий в новый метод в EventManager
:
private void addPersonToEvent(Long personId, Long eventId) { Session session = HibernateUtil.getSessionFactory().getCurrentSession(); session.beginTransaction();
Person aPerson = (Person) session.load(Person.class, personId); Event anEvent = (Event) session.load(Event.class, eventId); aPerson.getEvents().add(anEvent);
session.getTransaction().commit(); }
После загрузки Person
и Event
просто измените коллекцию, используя обычные методы
коллекций. Явный вызов update()
или save()
не нужен. Hibernate автоматически определяет,
что коллекция была изменена и нуждается в обновлении. Это называется
автоматической грязной проверкой (automatic dirty checking). Вы также можете попробовать это,
изменив имя или свойство даты любого из ваших объектов. Пока они находятся
в постоянном (persistent) состоянии, то есть связаны с определенным
org.hibernate.Session
, Hibernate контролирует любые изменения и выполняет SQL
в стиле запись-после (write-behind). Процесс синхронизации состояния памяти с базой данных происходящий,
как правило, только в конце единицы работы, называется промывкой (flushing).
В нашем коде единица работы заканчивается фиксацией (commit) или откатом (rollback) транзакции базы данных.
Вы можете загрузить человека и событие в разных единицах работы. Или вы можете изменить
объект за пределами org.hibernate.Session
, если он не находится
в постоянном (persistent) состоянии (если он был постоянным (persistent) раньше, это состояние
называется отсоединенным (detached)). Вы можете даже модифицировать коллекцию при её отсоединении:
private void addPersonToEvent(Long personId, Long eventId) { Session session = HibernateUtil.getSessionFactory().getCurrentSession(); session.beginTransaction();
Person aPerson = (Person) session .createQuery("select p from Person p left join fetch p.events where p.id = :pid") .setParameter("pid", personId) .uniqueResult(); // Eager fetch the collection so we can use it detached Event anEvent = (Event) session.load(Event.class, eventId);
session.getTransaction().commit();
// End of first unit of work aPerson.getEvents().add(anEvent); // aPerson (and its collection) is detached
// Begin second unit of work Session session2 = HibernateUtil.getSessionFactory().getCurrentSession(); session2.beginTransaction(); session2.update(aPerson); // Reattachment of aPerson
session2.getTransaction().commit(); }
Вызов update
снова сделает отсоединёный (detached) объект постоянным (persistent),
привязывая его к новой единице работы, поэтому любые изменения, внесенные вами в отсоединёном (detached)
состоянии, могут быть сохранены в базе данных. Сюда входят любые изменения (добавление/удаление),
которые вы сделали в коллекции этого объекта.
Это не очень полезно в нашем примере, но это важная концепция, которую вы можете включить
в свое приложение. Завершите это упражнение, добавив новое действие к основному методу
EventManager
и вызовите его из командной строки. Если вам нужны идентификаторы человека
и события — метод save()
возвратит их (возможно, вам придется изменить некоторые
из предыдущих методов, чтобы они возвращали этот идентификатор):
else if (args[0].equals("addpersontoevent")) { Long eventId = mgr.createAndStoreEvent("My Event", new Date()); Long personId = mgr.createAndStorePerson("Foo", "Bar"); mgr.addPersonToEvent(personId, eventId); System.out.println("Added person " + personId + " to event " + eventId); }
Это пример ассоциации между двумя одинаково важными классами: двумя сущностями. Как упоминалось ранее,
в типичной модели есть другие классы и типы, обычно «менее важные». Некоторые из них
вы уже видели, например, int
или java.lang.String
. Мы называем эти классы
типами значений (value types), а их экземпляры зависят от конкретного объекта.
Экземпляры этих типов не имеют собственной идентичности и не разделяются между сущностями.
Два человека не ссылаются на один и тот же объект firstname
,
даже если они имеют одинаковое имя. Типы значений не могут быть найдены только в JDK,
но вы также можете сами писать зависимые классы, такие как класс Address
или MonetaryAmount
. Фактически, в приложении Hibernate все классы JDK считаются типами значений.
Вы также можете создать коллекцию типов значений. Это концептуально отличается от набора ссылок
на другие объекты, но на Java практически одинаково.
1.2.4. Коллекия значений
Давайте добавим коллекцию адресов электронной почты к объекту Person
. Это будет представлено
как java.util.Set
экземпляров java.lang.String
:
private Set emailAddresses = new HashSet();
public Set getEmailAddresses() { return emailAddresses; }
public void setEmailAddresses(Set emailAddresses) { this.emailAddresses = emailAddresses; }
Отображение этого Set
выглядит следующим образом:
<set name="emailAddresses" table="PERSON_EMAIL_ADDR"> <key column="PERSON_ID"/> <element type="string" column="EMAIL_ADDR"/> </set>
Разница по сравнению с более ранним отображением заключается в использовании части элемента,
которая сообщает Hibernate, что коллекция не содержит ссылок на другой объект,
а скорее представляет собой набор, элементы которого являются типами значений,
здесь конкретно типа string
. В нижнем регистре указано, что это отображение type/converter.
Снова атрибут table
элемента set
определяет имя таблицы для коллекции.
Ключевой элемент определяет имя столбца внешнего ключа в таблице коллекции.
Атрибут column
в элементе element
определяет имя столбца, в котором
значения адреса электронной почты будут фактически сохранены.
Вот обновленная схема:
_____________ __________________ | | | | _____________ | EVENTS | | PERSON_EVENT | | | ___________________ |_____________| |__________________| | PERSON | | | | | | | |_____________| | PERSON_EMAIL_ADDR | | *EVENT_ID | <--> | *EVENT_ID | | | |___________________| | EVENT_DATE | | *PERSON_ID | <--> | *PERSON_ID | <--> | *PERSON_ID | | TITLE | |__________________| | AGE | | *EMAIL_ADDR | |_____________| | FIRSTNAME | |___________________| | LASTNAME | |_____________|
Вы можете видеть, что первичный ключ таблицы коллекции на самом деле является составным ключом,
который использует оба столбца. Это также подразумевает, что не должно быть одинаковых адресов
электронной почты на человека, что является именно семантикой, необходимой для установки в Java.
Теперь вы можете попробовать добавить элементы в эту коллекцию, как и раньше,
связывая людей и события. Это тот же код в Java:
private void addEmailToPerson(Long personId, String emailAddress) { Session session = HibernateUtil.getSessionFactory().getCurrentSession(); session.beginTransaction(); Person aPerson = (Person) session.load(Person.class, personId); // adding to the emailAddress collection might trigger a lazy load of the collection aPerson.getEmailAddresses().add(emailAddress); session.getTransaction().commit(); }
На этот раз мы не использовали запрос на выборку (fetch) для инициализации коллекции.
Проверьте журнал SQL и попытайтесь оптимизировать его с помощью надежной выборки.
1.2.5. Двунаправленные ассоциации
Затем вы отобразите двунаправленную ассоциацию. Вы создадите связь между человеком и событием
с обеих сторон в Java. Схема базы данных не изменяется, поэтому вы все равно будете иметь
связь «многие-ко-многим».
Заметка
Реляционная база данных более гибкая, чем язык сетевого программирования, поскольку она не требует
направления навигации; данные можно просматривать и извлекать любым возможным способом.
Сначала добавьте коллекцию участников в класс Event:
private Set participants = new HashSet();
public Set getParticipants() { return participants; }
public void setParticipants(Set participants) { this.participants = participants; }
Теперь отобразите эту сторону ассоциации в Event.hbm.xml
<set name="participants" table="PERSON_EVENT" inverse="true"> <key column="EVENT_ID"/> <many-to-many column="PERSON_ID" class="Person"/> </set>
Это нормальные Set
-отображения в обоих документах. Обратите внимание,
что имена столбцов в key
и «many-to-many
» меняются
в обоих документах. Наиболее важным дополнением здесь является атрибут inverse=«true»
в наборе элементов сопоставления коллекции Event
.
1.2.6. Работа двунаправленных связей
Во-первых, имейте в виду, что Hibernate не влияет на обычную семантику Java. Как мы создали
связь между Person
и Event
в однонаправленном примере? Вы добавляете
экземпляр Event
в коллекцию ссылок на события экземпляра Person
. Если
вы хотите сделать эту ссылку двунаправленной, вы должны сделать то же самое с другой стороны,
добавив ссылку Person
в коллекцию в Event
. Этот процесс
«установления связи с обеих сторон» абсолютно необходим с двунаправленными ссылками.
Многие разработчики программируют аккуратно и создают методы управления ссылками для правильной установки
обеих сторон (например, в Person
):
protected Set getEvents() { return events; }
protected void setEvents(Set events) { this.events = events; }
public void addToEvent(Event event) { this.getEvents().add(event); event.getParticipants().add(this); }
public void removeFromEvent(Event event) { this.getEvents().remove(event); event.getParticipants().remove(this); }
Методы get и set для коллекции теперь защищены. Это позволяет классам в одном и том же
пакете и подклассах продолжать доступ к этим методам, но не позволяет всем другим напрямую
изменять коллекции. Повторите шаги для коллекции на другой стороне.
Как насчет атрибута обратного (inverse)
отображения? Для вас и для Java двунаправленная
связь — это просто вопрос правильной установки ссылок с обеих сторон. Однако для Hibernate
недостаточно информации, чтобы правильно расположить инструкции SQL INSERT
и UPDATE
(чтобы избежать нарушения ограничений). Если одна сторона ассоциации обратная (inverse)
«говорит» Hibernate рассмотреть ее как зеркало (mirror) с другой стороны.
Это все, что необходимо для Hibernate чтобы разрешить любые проблемы, возникающие при преобразовании направленной
навигационной модели в схему базы данных SQL. Правила просты: все двунаправленные ассоциации нуждаются
в одной стороне как в обратной (inverse)
. В ассоциации «один-ко-многим»
это должно быть многостороннее, а в ассоциации «многие-ко-многим» вы можете
выбрать любую сторону.
1.3. Часть 3 — приложение Менеджер событий
Веб-приложение Hibernate использует Session
и Transaction
почти как автономное
приложение. Однако некоторые общие шаблоны полезны. Теперь вы можете написать EventManagerServlet
.
Этот сервлет может отображать все события, хранящиеся в базе данных, и предоставляет форму HTML
для ввода новых событий.
1.3.1. Написание основного сервлета
Сначала нам нужно создать наш основной сервлет обработки. Поскольку наш сервлет обрабатывает только HTTP-запросы
GET-запросы, мы реализуем только метод doGet()
:
package org.hibernate.tutorial.web;
// Imports public class EventManagerServlet extends HttpServlet {
protected void doGet( HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { SimpleDateFormat dateFormatter = new SimpleDateFormat( "dd.MM.yyyy" );
try { // Begin unit of work HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
// Process request and render page... // End unit of work HibernateUtil.getSessionFactory().getCurrentSession().getTransaction().commit(); } catch (Exception ex) { HibernateUtil.getSessionFactory().getCurrentSession().getTransaction().rollback(); if ( ServletException.class.isInstance( ex ) ) { throw ( ServletException ) ex; } else { throw new ServletException( ex ); } } } }
Сохраните код сервлета в src/main/java/org/hibernate/tutorial/web/EventManagerServlet.java
Образец, применяемый здесь, называется сессия-за-запрос (session-per-request). Когда запрос
попадает в сервлет, новый Hibernate Session
открывается через первый вызов
getCurrentSession()
в SessionFactory
. Затем запускается транзакция
с базой данных. Весь доступ к данным происходит внутри транзакции независимо от того,
читаются или записываются данные. Не используйте режим автоматической фиксации (auto-commit)
в приложениях.
Не используйте новый Hibernate Session
для каждой операции с базой данных.
Используйте один Hibernate Session
, охваченный (scoped) всем запросом. Используйте
getCurrentSession()
, чтобы он автоматически привязывался к текущему потоку Java.
Затем обрабатываются возможные действия запроса и визуализируется ответ HTML.
Скоро мы перейдем к этой части.
Наконец, единица работы заканчивается, когда обработка и визуализация завершены. Если во время обработки
или визуализации возникли какие-либо проблемы, будет выброшено исключение и транзакция базы данных будет
откачена (rolled back). Это завершает шаблон сессия-за-запрос (session-per-request)
.
Вместо разграничения кода транзакций в каждом сервлете вы также можете написать фильтр сервлета.
См. Веб-сайт Hibernate и Wiki для получения дополнительной информации об этом шаблоне,
называемом Open Session in View. Вам понадобится это, как только вы подумаете о визуализации
вашего представления в JSP, а не в сервлете.
1.3.2. Обработка и визуализация
Теперь вы можете реализовать обработку запроса и рендеринг страницы.
// Write HTML header PrintWriter out = response.getWriter(); out.println("<html><head><title>Event Manager</title></head><body>");
// Handle actions if ( "store".equals(request.getParameter("action")) ) {
String eventTitle = request.getParameter("eventTitle"); String eventDate = request.getParameter("eventDate");
if ( "".equals(eventTitle) || "".equals(eventDate) ) { out.println("<b><i>Please enter event title and date.</i></b>"); } else { createAndStoreEvent(eventTitle, dateFormatter.parse(eventDate)); out.println("<b><i>Added event.</i></b>"); } }
// Print page printEventForm(out); listEvents(out, dateFormatter);
// Write HTML footer out.println("</body></html>"); out.flush(); out.close();
Этот стиль кодирования с сочетанием Java и HTML не будет масштабироваться в более сложном
приложении. Имейте в виду, что мы только иллюстрируем основные концепции Hibernate в этом учебнике.
Код печатает HTML-заголовок и нижний колонтитул. На этой странице печатается HTML-форма для записи
события и список всех событий в базе данных. Первый метод тривиален и выводит только HTML:
private void printEventForm(PrintWriter out) { out.println("<h2>Add new event:</h2>"); out.println("<form>"); out.println("Title: <input name='eventTitle' length='50'/><br/>"); out.println("Date (e.g. 24.12.2009): <input name='eventDate' length='10'/><br/>"); out.println("<input type='submit' name='action' value='store'/>"); out.println("</form>"); }
Метод listEvents()
использует сессию Hibernate для привязки к текущему потоку для выполнения
запроса:
private void listEvents(PrintWriter out, SimpleDateFormat dateFormatter) {
List result = HibernateUtil.getSessionFactory() .getCurrentSession().createCriteria(Event.class).list(); if (result.size() > 0) { out.println("<h2>Events in database:</h2>"); out.println("<table border='1'>"); out.println("<tr>"); out.println("<th>Event title</th>"); out.println("<th>Event date</th>"); out.println("</tr>"); Iterator it = result.iterator(); while (it.hasNext()) { Event event = (Event) it.next(); out.println("<tr>"); out.println("<td>" + event.getTitle() + "</td>"); out.println("<td>" + dateFormatter.format(event.getDate()) + "</td>"); out.println("</tr>"); } out.println("</table>"); } }
Наконец, действие хранилища отправляется методу createAndStoreEvent()
,
который также использует сессию текущего потока:
protected void createAndStoreEvent(String title, Date theDate) { Event theEvent = new Event(); theEvent.setTitle(title); theEvent.setDate(theDate);
HibernateUtil.getSessionFactory() .getCurrentSession().save(theEvent); }
Сервлет завершен. Запрос к сервлету будет обрабатываться в течение одной сессии и транзакции.
Как ранее в автономном приложении, Hibernate может автоматически привязывать эти объекты к текущему
потоку выполнения. Это дает вам свободу сложить ваш код и получить доступ к SessionFactory
любым удобным вам способом. Обычно вы должны использовать более сложный дизайн и перемещать код доступа
к данным в объекты доступа к данным (шаблон DAO). См. Hibernate Wiki для получения дополнительных
примеров.
1.3.3. Развёртывание и тестирование
Чтобы развернуть это приложение для тестирования, мы должны создать Web ARchive (WAR). Сначала
мы должны определить дескриптор WAR как src/main/webapp/WEB-INF/web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet> <servlet-name>Event Manager</servlet-name> <servlet-class>org.hibernate.tutorial.web.EventManagerServlet</servlet-class> </servlet>
<servlet-mapping> <servlet-name>Event Manager</servlet-name> <url-pattern>/eventmanager</url-pattern> </servlet-mapping> </web-app>
Чтобы создать и развернуть пакет вызовите mvn
в каталоге проекта и скопируйте
файл hibernate-tutorial.war
в каталог webapps
сервера Tomcat.
Заметка
Реляционная база данных более гибкая, чем язык сетевого программирования, поскольку она не требует
направления навигации; данные можно просматривать и извлекать любым возможным способом.
После развертывания запустите приложение в http://localhost:8080/hibernate-tutorial/eventmanager
.
Убедитесь, что вы смотрели журнал Tomcat, чтобы увидеть, что Hibernate инициализируется, когда первый запрос
попадает на ваш сервлет (вызывается статический инициализатор в HibernateUtil
)
и получает подробный вывод, если происходят какие-либо исключения.
1.4. Резюме
В этом учебном пособии рассмотрены основы написания простого автономного приложения Hibernate
и небольшого веб-приложения. Дополнительные учебные материалы доступны на веб-сайте
Hibernate.