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All JPA Annotations: Mapping Annotations

Let's take a look at all the jpa mapping annotations..

Ramesh Fadatare user avatar

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This article provides you with 89 JPA mapping annotations for quick reference and/or summary. Let's get started!

Learn JPA in depth at  Java Persistence API Tutorial

JPA Annotations

2. @AssociationOverride

3. @AssociationOverrides

4. @AttributeOverride

5. @AttributeOverrides

7. @Cacheable

8. @CollectionTable

10. @ColumnResult

11. @ConstructorResult

12. @Convert

13. @Converter

14. @Converts

15. @DiscriminatorColumn

16. @DiscriminatorValue

17. @ElementCollection

18. @Embeddable

19. @Embedded

20. @EmbeddedId

21. @Entity

22. @EntityListeners

23. @EntityResult

24. @Enumerated

25. @ExcludeDefaultListeners

26. @ExcludeSuperclassListeners

27. @FieldResult

28. @ForeignKey

29. @GeneratedValue

31. @IdClass

33. @Inheritance

34. @JoinColumn

35. @JoinColumns

36. @JoinTable

38. @ManyToMany

39. @ManyToOne

40. @MapKey

41. @MapKeyClass

42. @MapKeyColumn

43. @MapKeyEnumerated

44. @MapKeyJoinColumn

45. @MapKeyJoinColumns

46. @MapKeyTemporal

47. @MappedSuperclass

48. @MapsId

49. @NamedAttributeNode

50. @NamedEntityGraph

51. @NamedEntityGraphs

52. @NamedNativeQueries

53. @NamedNativeQuery

54. @NamedQueries

55. @NamedQuery

56. @NamedStoredProcedureQueries

57. @NamedStoredProcedureQuery

58. @NamedSubgraph

59. @OneToMany

60. @OneToOne

61. @OrderBy

62. @OrderColumn

63. @PersistenceContext

64. @PersistenceContexts

65. @PersistenceProperty

66. @PersistenceUnit

67. @PersistenceUnits

68. @PostLoad

69. @PostPersist

70. @PostRemove

71. @PostUpdate

72. @PrePersist

73. @PreRemove

74. @PreUpdate

75. @PrimaryKeyJoinColumn

76. @PrimaryKeyJoinColumns

77. @QueryHint

78. @SecondaryTable

79. @SecondaryTables

80. @SequenceGenerator

81. @SqlResultSetMapping

82. @SqlResultSetMappings

83. @StoredProcedureParameter

85. @TableGenerator

86. @Temporal

87. @Transient

88. @UniqueConstraint

89. @Version

Let's describe each annotation with links to their Java doc and their official documentation sections.

The  @Access  annotation is used to specify the access type of the associated entity class, mapped superclass, or the embeddable class and entity attribute.

See the  Access type  section for more info.

@AssociationOverride

The  @AssociationOverride  annotation is used to override an association mapping (e.g.   @ManyToOne ,  @OneToOne ,  @OneToMany ,  @ManyToMany ) inherited from a mapped superclass or an embeddable.

See the  Overriding Embeddable types  section for more info.

@AssociationOverrides

The  @AssociationOverrides  is used to group several  @AssociationOverride  annotations.

@AttributeOverride

The  @AttributeOverride  annotation is used to override an attribute mapping inherited from a mapped superclass or an embeddable.

@AttributeOverrides

The  @AttributeOverrides  is used to group several  @AttributeOverride  annotations.

The  @Basic  annotation is used to map a basic attribute type to a database column.

See the  Basic types  chapter for more info.

The  @Cacheable  annotation is used to specify whether an entity should be stored in the second-level cache.

See the  Caching  chapter for more info.

@CollectionTable

The  @CollectionTable  annotation is used to specify the database table that stores the values of a basic or an embeddable type collection.

See the  Collections of embeddable types  section for more info.

The  @Column  annotation is used to specify the mapping between a basic entity attribute and the database table column.

See the  @Column annotation  section for more info.

@ColumnResult

The  @ColumnResult  annotation is used in conjunction with the  @SqlResultSetMapping  or  @ConstructorResult  annotations to map a SQL column for a given SELECT query.

See the  Entity associations with the named native queries  section for more info.

@ConstructorResult

The  @ConstructorResult  annotation is used in conjunction with the  @SqlResultSetMapping  annotations to map columns of a given SELECT query to a certain object constructor.

See the  Multiple scalar values NamedNativeQuery with ConstructorResult  section for more info.

The  @Convert  annotation is used to specify the  AttributeConverter  implementation used to convert the currently annotated basic attribute.

See the  AttributeConverter  section for more info.

24.1.13. @Converter

The  @Converter  annotation is used to specify that the current annotate  AttributeConverter  implementation can be used as a JPA basic attribute converter.

The  @Converts  annotation is used to group multiple  @Convert  annotations.

@DiscriminatorColumn

The  @DiscriminatorColumn  annotation is used to specify the discriminator column name and the  discriminator type  for the SINGLE_TABLE and JOINED Inheritance strategies.

See the  Discriminator  section for more info.

@DiscriminatorValue

The  @DiscriminatorValue  annotation is used to specify what value of the discriminator column is used for mapping the currently annotated entity.

@ElementCollection

The  @ElementCollection  annotation is used to specify a collection of basic or embeddable types.

See the  Collections  section for more info.

@Embeddable

The  @Embeddable  annotation is used to specify embeddable types. Like basic types, embeddable types do not have any identity, being managed by their owning entity.

See the  Embeddables  section for more info.

The  @Embedded  annotation is used to specify that a given entity attribute represents an embeddable type.

@EmbeddedId

The  @EmbeddedId  annotation is used to specify the entity identifier is an embeddable type.

See the  Composite identifiers with @EmbeddedId  section for more info.

The  @Entity  annotation is used to specify that the currently annotate class represents an entity type. Unlike basic and embeddable types, entity types have an identity and their state is managed by the underlying Persistence Context.

See the  Entity  section for more info.

@EntityListeners

The  @EntityListeners  annotation is used to specify an array of callback listener classes that are used by the currently annotated entity.

See the  JPA callbacks  section for more info.

@EntityResult

The  @EntityResult  annotation is used with the  @SqlResultSetMapping  annotation to map the selected columns to an entity.

@Enumerated

The  @Enumerated  annotation is used to specify that an entity attribute represents an enumerated type.

See the  @Enumerated basic type  section for more info.

@ExcludeDefaultListeners

The  @ExcludeDefaultListeners  annotation is used to specify that the currently annotated entity skips the invocation of any default listener.

See the  Exclude default entity listeners  section for more info.

@ExcludeSuperclassListeners

The  @ExcludeSuperclassListeners  annotation is used to specify that the currently annotated entity skips the invocation of listeners declared by its superclass.

@FieldResult

The  @FieldResult  annotation is used with the  @EntityResult  annotation to map the selected columns to the fields of some specific entity.

@ForeignKey

The  @ForeignKey  annotation is used to specify the associated foreign key of a  @JoinColumn  mapping. The  @ForeignKeyannotation  is only used if the automated schema generation tool is enabled. In which case, it allows you to customize the underlying foreign key definition.

See the  @ManyToOne with @ForeignKey  section for more info.

@GeneratedValue

The  @GeneratedValue  annotation specifies that the entity identifier value is automatically generated using an identity column, a database sequence, or a table generator. Hibernate supports the  @GeneratedValue  mapping even for UUIDidentifiers.

See the  Automatically-generated identifiers  section for more info.

The  @Id  annotation specifies the entity identifier. An entity must always have an identifier attribute, which is used when loading the entity in a given Persistence Context.

See the  Identifiers  section for more info.

The  @IdClass  annotation is used if the current entity defined a composite identifier. A separate class encapsulates all the identifier attributes, which are mirrored by the current entity mapping.

See the  Composite identifiers with @IdClass  section for more info.

The  @Index  annotation is used by the automated schema generation tool to create a database index.

See the  Columns index  chapter for more info.

24.1.33. @Inheritance

The  @Inheritance  annotation is used to specify the inheritance strategy of a given entity class hierarchy.

See the  Inheritance  section for more info.

@JoinColumn

The  @JoinColumn  annotation is used to specify the FOREIGN KEY column used when joining an entity association or an embeddable collection.

See the  @ManyToOne with @JoinColumn  section for more info.

@JoinColumns

The  @JoinColumns  annotation is used to group multiple  @JoinColumn  annotations, which are used when mapping entity association or an embeddable collection using a composite identifier

The  @JoinTable  annotation is used to specify the link table between two other database tables.

See the  @JoinTable mapping  section for more info.

The  @Lob  annotation is used to specify that the currently annotated entity attribute represents a large object type.

See the  BLOB mapping  section for more info.

@ManyToMany

The  @ManyToMany  annotation is used to specify a many-to-many database relationship.

See the  @ManyToMany mapping  section for more info.

The  @ManyToOne  annotation is used to specify a many-to-one database relationship.

See the  @ManyToOne mapping  section for more info.

The  @MapKey  annotation is used to specify the key of a java.util.Map association for which the key type is either the primary key or an attribute of the entity that represents the value of the map.

See the  @MapKey mapping  section for more info.

@MapKeyClass

The  @MapKeyClass  annotation is used to specify the type of the map key of a java.util.Map associations.

See the  @MapKeyClass mapping  section for more info.

@MapKeyColumn

The  @MapKeyColumn  annotation is used to specify the database column, which stores the key of a java.util.Mapassociation for which the map key is a basic type.

See the  @MapKeyType mapping section  for an example of  @MapKeyColumn  annotation usage.

@MapKeyEnumerated

The  @MapKeyEnumerated  annotation is used to specify that the key of java.util.Map association is a Java Enum.

See the  @MapKeyEnumerated mapping  section for more info.

@MapKeyJoinColumn

The  @MapKeyJoinColumn  annotation is used to specify that the key of java.util.Map association is an entity association. The map key column is a FOREIGN KEY in a link table that also joins the Map owner’s table with the table where the Map value resides.

See the  @MapKeyJoinColumn mapping  section for more info.

@MapKeyJoinColumns

The  @MapKeyJoinColumns  annotation is used to group several  @MapKeyJoinColumn  mappings when the java.util.Map association key uses a composite identifier.

@MapKeyTemporal

The  @MapKeyTemporal  annotation is used to specify that the key of java.util.Map association is a  @TemporalType  (e.g. DATE, TIME, TIMESTAMP).

See the  @MapKeyTemporal mapping  section for more info.

@MappedSuperclass

The  @MappedSuperclass  annotation is used to specify that the currently annotated type attributes are inherited by any subclass entity.

See the  @MappedSuperclass  section for more info.

The  @MapsId  annotation is used to specify that the entity identifier is mapped by the currently annotated  @ManyToOne   or  @OneToOne   association.

See the  @MapsId mapping  section for more info.

@NamedAttributeNode

The  @NamedAttributeNode  annotation is used to specify each individual attribute node that needs to be fetched by an Entity Graph.

See the  Fetch graph  section for more info.

@NamedEntityGraph

The  @NamedEntityGraph  annotation is used to specify an Entity Graph that can be used by an entity query to override the default fetch plan.

@NamedEntityGraphs

The  @NamedEntityGraphs  annotation is used to group multiple  @NamedEntityGraph  annotations.

24.1.52. @NamedNativeQueries

The  @NamedNativeQueries  annotation is used to group multiple  @NamedNativeQuery  annotations.

See the  Custom CRUD mapping  section for more info.

@NamedNativeQuery

The  @NamedNativeQuery  annotation is used to specify a native SQL query that can be retrieved later by its name.

@NamedQueries

The  @NamedQueries  annotation is used to group multiple  @NamedQuery  annotations.

@NamedQuery

The  @NamedQuery  annotation is used to specify a JPQL query that can be retrieved later by its name.

See the  @NamedQuery  section for more info.

@NamedStoredProcedureQueries

The  @NamedStoredProcedureQueries  annotation is used to group multiple  @NamedStoredProcedureQuery  annotations.

@NamedStoredProcedureQuery

The  @NamedStoredProcedureQuery  annotation is used to specify a stored procedure query that can be retrieved later by its name.

See the  Using named queries to call stored procedures  section for more info.

@NamedSubgraph

The  @NamedSubgraph  annotation used to specify a subgraph in an Entity Graph.

See the  Fetch subgraph  section for more info.

The  @OneToMany  annotation is used to specify a one-to-many database relationship.

See the  @OneToMany mapping  section for more info.

The  @OneToOne  annotation is used to specify a one-to-one database relationship.

See the  @OneToOne mapping  section for more info.

The  @OrderBy  annotation is used to specify the entity attributes used for sorting when fetching the currently annotated collection.

See the  @OrderBy mapping  section for more info.

@OrderColumn

The  @OrderColumn  annotation is used to specify that the current annotation collection order should be materialized in the database.

See the  @OrderColumn mapping  section for more info.

@PersistenceContext

The  @PersistenceContext  annotation is used to specify the  EntityManager   that needs to be injected as a dependency.

See the  @PersistenceContext mapping  section for more info.

@PersistenceContexts

The  @PersistenceContexts  annotation is used to group multiple  @PersistenceContext  annotations.

@PersistenceProperty

The  @PersistenceProperty  annotation is used by the  @PersistenceContext  annotation to declare JPA provider properties that are passed to the underlying container when the  EntityManager   instance is created.

See the  @PersistenceProperty mapping  section for more info.

@PersistenceUnit

The  @PersistenceUnit  annotation is used to specify the  EntityManagerFactory   that needs to be injected as a dependency.

See the  @PersistenceUnit mapping  section for more info.

@PersistenceUnits

The  @PersistenceUnits  annotation is used to group multiple  @PersistenceUnit  annotations.

The  @PostLoad  annotation is used to specify a callback method that fires after an entity is loaded.

@PostPersist

The  @PostPersist  annotation is used to specify a callback method that fires after an entity is persisted.

@PostRemove

The  @PostRemove  annotation is used to specify a callback method that fires after an entity is removed.

@PostUpdate

The  @PostUpdate  annotation is used to specify a callback method that fires after an entity is updated.

@PrePersist

The  @PrePersist  annotation is used to specify a callback method that fires before an entity is persisted.

The  @PreRemove  annotation is used to specify a callback method that fires before an entity is removed.

The  @PreUpdate  annotation is used to specify a callback method that fires before an entity is updated.

@PrimaryKeyJoinColumn

The  @PrimaryKeyJoinColumn  annotation is used to specify that the primary key column of the currently annotated entity is also a foreign key to some other entity (e.g. a base class table in a JOINED inheritance strategy, the primary table in a secondary table mapping, or the parent table in a  @OneToOne   relationship).

See the  @PrimaryKeyJoinColumn mapping  section for more info.

@PrimaryKeyJoinColumns

The  @PrimaryKeyJoinColumns  annotation is used to group multiple  @PrimaryKeyJoinColumn  annotations.

The  @QueryHint  annotation is used to specify a JPA provider hint used by a  @NamedQuery  or a   @NamedNativeQueryannotation .

See the  @QueryHint  section for more info.

@SecondaryTable

The  @SecondaryTable  annotation is used to specify a secondary table for the currently annotated entity.

See the  @SecondaryTable mapping  section for more info.

@SecondaryTables

The  @SecondaryTables  annotation is used to group multiple  @SecondaryTable  annotations.

@SequenceGenerator

The  @SequenceGenerator  annotation is used to specify the database sequence used by the identifier generator of the currently annotated entity.

See the  @SequenceGenerator mapping  section for more info.

@SqlResultSetMapping

The  @SqlResultSetMapping  annotation is used to specify the  ResultSet   mapping of a native SQL query or stored procedure.

See the  SqlResultSetMapping mapping  section for more info.

@SqlResultSetMappings

The  @SqlResultSetMappings  annotation is used to group multiple  @SqlResultSetMapping  annotations.

@StoredProcedureParameter

The  @StoredProcedureParameter  annotation is used to specify a parameter of a  @NamedStoredProcedureQuery .

The  @Table  annotation is used to specify the primary table of the currently annotated entity.

See the  @Table mapping  section for more info.

@TableGenerator

The  @TableGenerator  annotation is used to specify the database table used by the identity generator of the currently annotated entity.

See the  @TableGenerator mapping  section for more info.

The  @Temporal  annotation is used to specify the  TemporalType   of the currently annotated java.util.Date or java.util.Calendar entity attribute.

See the  Basic temporal types  chapter for more info.

The  @Transient  annotation is used to specify that a given entity attribute should not be persisted.

See the  @Transient mapping  section for more info.

@UniqueConstraint

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 currently annotated entity.

See the  Columns unique constraint  chapter for more info.

The  @Version  annotation is used to specify the version attribute used for optimistic locking.

Published at DZone with permission of Ramesh Fadatare . See the original article here.

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Matthew Tyson

By Matthew Tyson , Contributor, JavaWorld |

Everything you need to know about Java programming tools and APIs, with code and examples.

What is JPA? Introduction to Java persistence

Get to know the java persistence standard based on hibernate and learn how to use jpa to store and manage java objects in a relational or nosql database..

what is jpa annotations

JPA and Hibernate

What is java orm, data persistence in java, metadata annotations in jpa, configuring jpa, entity relationships.

  • Fetching strategies
  • JPA installation and setup
  • When to use JPA

As a specification, the Jakarta Persistence API (formerly Java Persistence API) is concerned with persistence , which loosely means any mechanism by which Java objects outlive the application process that created them. Not all Java objects need to be persisted, but most applications persist key business objects. The JPA specification lets you define which objects should be persisted, and how they are persisted in your Java applications.

By itself, JPA is not a tool or framework; rather, it defines a set of concepts that guide implementers. While JPA's object-relational mapping (ORM) model was originally based on Hibernate , it has since evolved. Likewise, while JPA was originally intended for use with relational databases, some JPA implementations have been extended for use with NoSQL datastores. A popular framework that supports JPA with NoSQL is EclipseLink , the reference implementation for JPA 3.

The core idea behind JPA as opposed to JDBC , is that for the most part, JPA lets you avoid the need to “think relationally." In JPA, you define your persistence rules in the realm of Java code and objects, whereas JDBC requires you to manually translate from code to relational tables and back again.

Popular JPA implementations like Hibernate and EclipseLink now support JPA 3. Migrating from JPA 2 to JPA 3 involves some namespace changes , but otherwise the changes are under-the-hood performance gains.

Because of their intertwined history, Hibernate and JPA are frequently conflated. However, like the Java Servlet specification, JPA has spawned many compatible tools and frameworks. Hibernate is just one of many JPA tools.

Developed by Gavin King and first released in early 2002, Hibernate is an ORM library for Java. King developed Hibernate as an alternative to entity beans for persistence. The framework was so popular, and so needed at the time, that many of its ideas were adopted and codified in the first JPA specification.

Today, Hibernate ORM is one of the most mature JPA implementations, and still a popular option for ORM in Java. The latest release as of this writing, Hibernate ORM 6 , implements JPA 2.2. Additional Hibernate tools include Hibernate Search , Hibernate Validator , and Hibernate OGM , which supports domain-model persistence for NoSQL.

While they differ in execution, every JPA implementation provides some kind of ORM layer. In order to understand JPA and JPA-compatible tools, you need to have a good grasp on ORM.

Object-relational mapping is a task –one that developers have good reason to avoid doing manually. A framework like Hibernate ORM or EclipseLink codifies that task into a library or framework, an ORM layer . As part of the application architecture, the ORM layer is responsible for managing the conversion of software objects to interact with the tables and columns in a relational database. In Java, the ORM layer converts Java classes and objects so that they can be stored and managed in a relational database.

By default, the name of the object being persisted becomes the name of the table, and fields become columns. Once the table is set up, each table row corresponds to an object in the application. Object mapping is configurable, but defaults tend to work, and by sticking with defaults, you avoid having to maintain configuration metadata.

Figure 1 illustrates the role of JPA and the ORM layer in application development.

Figure 1. JPA and the Java ORM layer.

Configuring the Java ORM layer

When you set up a new project to use JPA, you will need to configure the datastore and JPA provider. You'll configure a datastore connector to connect to your chosen database (SQL or NoSQL). You'll also include and configure the JPA provider , which is a framework such as Hibernate or EclipseLink. While you can configure JPA manually, many developers choose to use Spring's out-of-the-box support. We'll take a look at both manual and Spring-based JPA installation and setup shortly.

From a programming perspective, the ORM layer is an adapter layer : it adapts the language of object graphs to the language of SQL and relational tables. The ORM layer allows object-oriented developers to build software that persists data without ever leaving the object-oriented paradigm.

When you use JPA, you create a map from the datastore to your application's data model objects. Instead of defining how objects are saved and retrieved, you define the mapping between objects and your database, then invoke JPA to persist them. If you're using a relational database, much of the actual connection between your application code and the database will then be handled by JDBC.

As a specification, JPA provides metadata annotations , which you use to define the mapping between objects and the database. Each JPA implementation provides its own engine for JPA annotations. The JPA spec also provides the PersistanceManager or EntityManager , which are the key points of contact with the JPA system (wherein your business logic code tells the system what to do with the mapped objects).

To make all of this more concrete, consider Listing 1, which is a simple data class for modeling a musician.

Listing 1. A simple data class in Java

The Musician class in Listing 1 is used to hold data. It can contain primitive data such as the name field. It can also hold relations to other classes such as mainInstrument and performances .

Musician 's reason for being is to contain data. This type of class is sometimes known as a DTO, or data transfer object . DTOs are a common feature of software development. While they hold many kinds of data, they do not contain any business logic. Persisting data objects is a ubiquitous challenge in software development.

Data persistence with JDBC

One way to save an instance of the Musician class to a relational database would be to use the JDBC library. JDBC is a layer of abstraction that lets an application issue SQL commands without thinking about the underlying database implementation.

Listing 2 shows how you could persist the Musician class using JDBC.

Listing 2. JDBC inserting a record

The code in Listing 2 is fairly self-documenting. The georgeHarrison object could come from anywhere (front-end submit, external service, etc.), and has its ID and name fields set. The fields on the object are then used to supply the values of an SQL insert statement. (The PreparedStatement class is part of JDBC, offering a way to safely apply values to an SQL query.)

While JDBC provides the control that comes with manual configuration, it is cumbersome compared to JPA. To modify the database, you first need to create an SQL query that maps from your Java object to the tables in a relational database. You then have to modify the SQL whenever an object signature changes. With JDBC, maintaining the SQL becomes a task in itself.

Data persistence with JPA

Now consider Listing 3, where we persist the Musician class using JPA.

Listing 3. Persisting George Harrison with JPA

Listing 3 replaces the manual SQL from Listing 2 with a single line, entityManager.save() , which instructs JPA to persist the object. From then on, the framework handles the SQL conversion, so you never have to leave the object-oriented paradigm.

The magic in Listing 3 is the result of a configuration , which is created using JPA's annotations . Developers use annotations to inform JPA which objects should be persisted, and how they should be persisted.

Listing 4 shows the Musician class with a single JPA annotation.

Listing 4. JPA's @Entity annotation

Persistent objects are sometimes called entities . Attaching @Entity to a class like Musician informs JPA that this class and its objects should be persisted.

Like most modern frameworks, JPA embraces coding by convention (also known as convention over configuration ), in which the framework provides a default configuration based on industry best practices. As one example, a class named Musician would be mapped by default to a database table called Musician.

The conventional configuration is a timesaver, and in many cases it works well enough. It is also possible to customize your JPA configuration. As an example, you could use JPA's @Table annotation to specify the table where the Musician class should be stored.

Listing 5. JPA's @Table annotation

Listing 5 tells JPA to persist the entity (the Musician class) to the Musician table.

Primary key

In JPA, the primary key is the field used to uniquely identify each object in the database. The primary key is useful for referencing and relating objects to other entities. Whenever you store an object in a table, you will also specify the field to use as its primary key.

In Listing 6, we tell JPA what field to use as Musician 's primary key.

Listing 6. Specifying the primary key

In this case, we've used JPA's @Id annotation to specify the id field as Musician 's primary key. By default, this configuration assumes the primary key will be set by the database--for instance, when the field is set to auto-increment on the table.

JPA supports other strategies for generating an object's primary key. It also has annotations for changing individual field names. In general, JPA is flexible enough to adapt to any persistence mapping you might need.

CRUD operations

Once you've mapped a class to a database table and established its primary key, you have everything you need to create, retrieve, delete, and update that class in the database. Calling entityManager.save() will create or update the specified class, depending on whether the primary-key field is null or applies to en existing entity. Calling entityManager.remove() will delete the specified class.

Simply persisting an object with a primitive field is only half the equation. JPA also lets you manage entities in relation to one another. Four kinds of entity relationships are possible in both tables and objects:

  • One-to-many
  • Many-to-one
  • Many-to-many

Each type of relationship describes how an entity relates to other entities. For example, the Musician entity could have a one-to-many relationship with Performance , an entity represented by a collection such as List or Set .

If the Musician included a Band field, the relationship between these entities could be many-to-one , implying a collection of Musician s on the single Band class. (Assuming each musician only performs in a single band.)

  • Data Management
  • Software Development

what is jpa annotations

JPA - Entity Annotations

A key feature of EJB 3.0 and JPA is the ability to create entities that contain object-relational mappings by using (metadata) annotations rather than deployment descriptors (orm.xml) as in earlier versions.

Jpa Mapping Method

JPA contains two type of annotations:

  • global annotations: Entity, Callback, Queries, Reference to EntityManager and EntityManagerFactory (see chapter 10 of the specification )
  • object-relational mappings annotations (chapter 11 of the specification )

See Annotation Type Summary for the list reference of all standard Annotations.

Articles Related

  • JPA - Object-Relational Mapping (ORM)

JPA - How to model a @Many-to-Many Relationship ?

JPA - How to define a @One-to-Many relationship ?

  • JPA - Getting Started - Hello World
  • JPA - Primary Key (@Id, @IdClass, )

Annotations

All Entity class is annotated with an @Entity annotation, since this is a requirement for every JPA entity.

  • catalog is different depending on the database vendor. In the case of MySQL, the catalog is simply the database name.

If there are any unique constraints, the uniqueConstraints attribute is added to the @Table annotation.

@XmlRootElement

This annotation is used by JAXB to map the entity to XML.

@NamedQueries

@NamedQueries annotation encapsulates all the generated @NamedQuery annotations.

JPA named queries allow to define Java Persistence Query Language (JPQL) queries right in the corresponding JPA entity, which means that the queries don't need to be hard-coded in the code.

JPQL queries defined in @NamedQuery annotations can be accessed through the createNamedQuery()method in the JPA EntityManager.

Identifiers preceded by a colon (:) are named parameters (known as bind variable in the Oracle Database) . These parameters need to be replaced by the appropriate values before executing the query, which is done by invoking the setParameter() method on a Query object.

Jpa Mapping Property

A basic property handles a standard value that is persisted as-is to the database. Every non-static non-transient property ( field or method ) of an entity bean is considered persistent .

The @Basic annotation allows to declare the fetching strategy.

The @Basic annotation is followed by the @Column annotation to define the property of the database column:

No annotation is equivalent to the @Basic annotation.

  • the optional attribute with a false value prevents from attempting to persist an entity with a null value for the field that this annotation decorates.

For each entity, you must designate at least one of the following:

  • one @EmbeddedId
  • multiple @Id and an @IdClass

Jpa Column Annotation

An Id property designates an identifier , such as a primary key .

All entity beans must declare one or more fields which together form the persistent identity of an instance.

An @Id annotation is followed by a @Column annotation defining the unique attribute.

@EmbeddedId is used to model composite primary keys which is defined with an additional class

@GeneratedValue

The JPA primary key generation strategy is denoted by the @GeneratedValue annotation.

The persistence provider needs to have a persistent resource, such as a table or a sequence. The persistence provider cannot always rely upon the database connection that it obtains from the server to have permissions to create a table in the database. There will need to be a creation phase or schema generation to cause the resource to be created before the strategy can function.

  • For attributes of type String, length to specify the maximum length allowed
  • For decimal types, the precision (number of digits in a number) and scale (number of digits to the right of the decimal point)

The attribute definitions of the column annotation are used for regenerating the database tables from the JPA entities whereas the @NotNull and the @Size annotations are part of Bean Validation (A new feature introduced in Java EE 6).

See Column Annotations Doc

Jpa Mapping Table

The access property define where the annotation are written:

  • Property: to the class's accessors (getter methods)
  • Field: to the class's fields .

Association Fetch

JPA - (Association) Fetch

Relationship

Bi-directional: A pet have an owner but an owner have also a pet (two directions).

@One-to-One

one-to-one relationship

The following @JoinColumn annotation declares the column in the (targeted|other) entity that will be used for the join.

@Many-to-one

To define a many-to-one relationship , the following annotations are used:

  • @Many-to-one: to define the cardinality
  • @JoinColumn: to give the column name which joins to the primary key of the outer table (by default) in order to define the join predicate

The many-to-one annotation can define a fetch attribute that specifies when the field's persisted data are loaded:

  • FetchType.EAGER: The data are loaded before the entity object is returned by the persistence provider.
  • FetchType.LAZY: The data are loaded later, when the property is accessed.

The many-to-one are defaulted to FetchType.EAGER.

@One-to-Many

@many-to-many, documentation / reference.

  • Specification API Annotations
  • Providers Extensions: Eclipse Link Annotation Extensions Reference.

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  • » JPA Callback Methods
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  • » CRUD Example
  • » All JPA Annotation
  • » @Entity Annotation
  • » @Table Annotation
  • » @Column Annotation
  • » @Embedded Annotation
  • » @EmbeddedId Annotation
  • » @Access Annotation
  • » @Transient Annotation
  • » @GeneratedValue Annotation
  • » @SequenceGenerator Annotation
  • » @TableGenerator Annotation
  • » @IdClass Annotation
  • » JPA EntityManager
  • » Associations In JPA
  • » Many-to-One Unidirectional Mapping
  • » One-to-Many Unidirectional Mapping
  • » One-to-Many Bidirectional Mapping
  • » Many-to-One Bidirectional Mapping
  • » One-to-One Unidirectional Mapping
  • » One-to-One Bidirectional Mapping
  • » Many-to-Many Bidirectional Mapping
  • » JPA Query
  • » Query Operators And Functions
  • » Deleting Updating Ordering in Query
  • » Query Parameters
  • » Named Queries
  • » JPA Criteria
  • » JPA Native Query

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JPA Annotations

In this tutorial we will list out all the JPA annotations. In this tutorial we are just listing out the annotations, annotation details and their examples will be studied in the subsequent chapters. JPA defines dozens of annotations that can be divided into the following groups:

Annotations for JPA aware classes:

JPA Annotations for Classes  

JPA defines three types of persistable classes which are set by the following annotations:

javax.persistence.Embeddable  

javax.persistence.Entity  

javax.persistence.MappedSuperclass  

Entity and mapped super classes can be further configured by annotations that specify cache preferences and lifecycle event listener policy.

javax.persistence.Cacheable  

javax.persistence.EntityListeners  

javax.persistence.ExcludeDefaultListeners  

javax.persistence.ExcludeSuperclassListeners  

Another JPA class annotation defines an ID class, ID classes are useful in representing composite primary keys.

javax.persistence.IdClass  

JPA Annotations for JPQL Queries  

The following annotations are used to define static named JPA queries:

javax.persistence.NamedQueries  

javax.persistence.NamedQuery  

javax.persistence.QueryHint  

Annotations for fields in JPA persistable classes:

JPA Annotations for Fields  

The way a field of a persistable class is managed by JPA can be set by the following annotations:

javax.persistence.Basic  

javax.persistence.Embedded  

javax.persistence.ElementCollection  

javax.persistence.Id  

javax.persistence.EmbeddedId  

javax.persistence.Version  

javax.persistence.Transient  

Additional annotations (and enum) are designated for enum fields:

javax.persistence.Enumerated  

javax.persistence.MapKeyEnumerated  

javax.persistence.EnumType  

Other additional annotations (and enum) are designated for date and calendar fields:

javax.persistence.Temporal  

javax.persistence.TemporalType  

javax.persistence.MapKeyTemporal  

JPA Annotations for Relationships  

Relationships are persistent fields in persistable classes that reference other entity objects. The four relationship modes are represented by the following annotations:

javax.persistence.ManyToMany  

javax.persistence.ManyToOne  

javax.persistence.OneToMany  

javax.persistence.OneToOne  

Unlike ORM JPA implementations, ObjectDB does not enforce specifying any of the annotations above. Specifying a relationship annotation enables configuring cascade and fetch policy, using the following enum types:

javax.persistence.CascadeType  

javax.persistence.FetchType  

Additional annotations are supported by ObjectDB for the inverse side of a bidirectional relationship (which is calculated by a query) :

javax.persistence.OrderBy  

javax.persistence.MapKey  

Annotations for additional JPA configuration:

JPA Annotations for Access Modes  

Persistence fields can either be accessed by JPA directly (as fields) or indirectly (as properties and get/set methods). JPA 2 provides an annotation and an enum for setting the access mode:

javax.persistence.Access  

javax.persistence.AccessType  

JPA Annotations for Value Generation  

Automatically generated values are mainly useful for primary key fields, but are supported by ObjectDB also for regular (non primary key) persistent fields. At the field level, the @GeneratedValue with an optional GenerationType strategy is specified:

javax.persistence.GeneratedValue  

javax.persistence.GenerationType  

The @GeneratedValue annotation can also reference a value generator, which is defined at the class level by using one of the following annotations:

javax.persistence.SequenceGenerator  

javax.persistence.TableGenerator  

Annotations for JPA lifecycle event callbacks:

JPA Annotations for Callback Methods  

The following annotations can mark methods as JPA callback methods:

javax.persistence.PrePersist  

javax.persistence.PreRemove  

javax.persistence.PreUpdate  

javax.persistence.PostLoad  

javax.persistence.PostPersist  

javax.persistence.PostRemove  

javax.persistence.PostUpdate  

Java EE container annotations:

JPA Annotations for Java EE  

The following JPA annotations are in use to integrate JPA into a Java EE application and are managed by the Java EE container:

javax.persistence.PersistenceContext  

javax.persistence.PersistenceContextType  

javax.persistence.PersistenceContexts  

javax.persistence.PersistenceProperty  

javax.persistence.PersistenceUnit  

javax.persistence.PersistenceUnits  

Many other JPA annotations are designated for Object Relational Mapping (ORM) JPA providers (for mapping between a relational database and an object model and for direct SQL queries):

JPA Annotations for Mapping (ORM)  

The following JPA annotations and enums are designated for mapping a JPA object model to a relational database.

javax.persistence.AssociationOverride  

javax.persistence.AssociationOverrides  

javax.persistence.AttributeOverride  

javax.persistence.AttributeOverrides  

javax.persistence.CollectionTable  

javax.persistence.Column  

javax.persistence.DiscriminatorColumn  

javax.persistence.DiscriminatorType  

javax.persistence.DiscriminatorValue  

javax.persistence.Inheritance  

javax.persistence.InheritanceType  

javax.persistence.JoinColumn  

javax.persistence.JoinColumns  

javax.persistence.JoinTable  

javax.persistence.Lob  

javax.persistence.MapKeyClass  

javax.persistence.MapKeyColumn  

javax.persistence.MapKeyJoinColumn  

javax.persistence.MapKeyJoinColumns  

javax.persistence.MapsId  

javax.persistence.OrderColumn  

javax.persistence.PrimaryKeyJoinColumn  

javax.persistence.PrimaryKeyJoinColumns  

javax.persistence.SecondaryTable  

javax.persistence.SecondaryTables  

javax.persistence.Table  

javax.persistence.UniqueConstraint  

JPA Annotations for SQL Queries  

The following JPA annotations are designated for SQL queries on relational databases:

javax.persistence.ColumnResult  

javax.persistence.EntityResult  

javax.persistence.FieldResult  

javax.persistence.NamedNativeQueries  

javax.persistence.NamedNativeQuery  

javax.persistence.SqlResultSetMapping  

javax.persistence.SqlResultSetMappings  

Annotations for Associations:

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All JPA Annotations: Mapping Annotations

Jpa mapping annotations, @associationoverride, @associationoverrides, @attributeoverride, @attributeoverrides, @collectiontable, @columnresult, @constructorresult, 24.1.13. @converter, @discriminatorcolumn, @discriminatorvalue, @elementcollection, @embeddable, @embeddedid, @entitylisteners, @entityresult, @enumerated, @excludedefaultlisteners, @excludesuperclasslisteners, @fieldresult, @foreignkey, @generatedvalue, @joincolumn, @joincolumns, @manytomany, @mapkeyclass, @mapkeycolumn, @mapkeyenumerated, @mapkeyjoincolumn, @mapkeyjoincolumns, @mapkeytemporal, @mappedsuperclass, @namedattributenode, @namedentitygraph, @namedentitygraphs, @namednativequery, @namedqueries, @namedquery, @namedstoredprocedurequeries, @namedstoredprocedurequery, @namedsubgraph, @ordercolumn, @persistencecontext, @persistencecontexts, @persistenceproperty, @persistenceunit, @persistenceunits, @postpersist, @postremove, @postupdate, @prepersist, @primarykeyjoincolumn, @primarykeyjoincolumns, @secondarytable, @secondarytables, @sequencegenerator, @sqlresultsetmapping, @sqlresultsetmappings, @storedprocedureparameter, @tablegenerator, @uniqueconstraint.

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Spring Boot Starter Data JPA

Spring Boot provides starter dependency spring-boot-starter-data-jpa to connect Spring Boot application with relational database efficiently. The spring-boot-starter-data-jpa internally uses the spring-boot-jpa dependency.

Spring Boot JPA Example

Let's create a Spring Boot application that uses JPA to connect to the database. In the following example, we have used in-memory database Apache Derby.

Apache Derby: It is an open-source, embedded relational database implemented entirely in Java. It is available under the Apache License 2.0. There are following advantages of Apache Derby:

  • It is easy to install, deploy, and use.
  • It is based on Java, JDBC, and SQL standards.
  • It provides an embedded JDBC driver that allows us to embed Derby in any Java-based solution.
  • It also supports client/server mode with the Derby Network Client JDBC driver, and Derby Network Server.

Spring Boot can auto-configure an embedded database such as H2, HSQL, and Derbydatabases . We do not need to provide any connection URLs. We need only include a build dependency on the embedded database that we want to use.

In Spring Boot, we can easily integrate Apache Derby database just by adding Derby dependency in pom.xml file.

Step 1: Open Spring Initializr https://start.spring.io/ .

Step 2: Select the latest version of Spring Boot 2.3.0(SNAPSHOT)

Step 3: Provide the Group name. We have provided com.javatpoint.

Step 4: Provide the Artifact Id. We have provided apache-derby-example .

Step 5: Add the dependencies: Spring Web, Spring Data JPA, and Apache Derby Database .

Step 6: Click on the Generate button. When we click on the Generate button, it wraps the project in a Jar file and downloads it to the local system.

Spring Boot jpa

Step 7: Extract the Jar file and paste it into the STS workspace.

Step 8: Import the project folder into STS.

File -> Import -> Existing Maven Projects -> Browse -> Select the folder apache-derby-example -> Finish

It takes some time to import.

Step 9: Create a package with the name com.javatpoint.model in the folder src/main/java.

Step 10: Create a class with the name UserRecord in the package com.javatpoint.model and do the following:

  • Define three variables id, name, and email .
  • Generate Getters and Setter. Right-click on the file -> Source -> Generate Getters and Setters
  • Define a default constructor.
  • Mark the class as an Entity by using the annotation @Entity.
  • Mark Id as the primary key by using the annotation @Id.

UserRecord.java

Step 11: Create a package with the name com.javatpoint.controller in the folder src/main/java.

Step 12: Create a Controller class with the name UserController in the package com.javatpoint.controller and do the following:

  • Mark the class as a controller by using the annotation @RestController.
  • Autowired the class UserService by using the annotation @Autowired .
  • We have defined two mappings, one for getting all users and the other for add-user.

UserController.java

Step 13: Create a package with the name com.javatpoint.service in the folder src/main/java.

Step 14: Create a Service class with the name UserService in the package com.javatpoint.service and do the following:

  • Mark the class as service by using the annotation @Service.
  • Autowired the UserRepository
  • Define a method getAllUsers() that returns a List of
  • Define another method name addUser() that saves the user record.

UserService.java

Step 15: Create a package with the name com.javatpoint.repository in the folder src/main/java.

Step 16: Create a repository interface with the name UserRepository in the package com.javatpoint.repository and extends CrudRepository .

UserRepository.java

Step 17: Now, open the ApacheDerbyExampleApplication.java file. It created by default when we set-up an application.

ApacheDerbyExampleApplication.java

Now, we have set-up all the necessary classes and packages according to the requirements. Notice that we have not provided any connection URL for the database. After completing all the above steps, the project directory looks like the following:

Spring Boot jpa

Let's run the application.

Step 18: Open the ApacheDerbyExampleApplication.java file and run it as Java Application.

Step 19: Open the browser and invoke the URL http://localhost:8080/. It returns an empty list because we have not added any user in the List.

To add a user to the database, we will send a POST request by using the Postman .

Step 20: Open the Postman and do the following:

  • Select the POST
  • Invoke the URL http://localhost:8080/add-user.
  • Click on the Body
  • Select Content-Type as JSON (application/json).
  • Insert the data which want to insert in the database. We have inserted the following data:
  • Click on the Send button.

Spring Boot jpa

When we click on the Send button, it shows Status:200 OK . It means the request has been successfully executed.

Step 21: Open the browser and invoke the URL http://localhost:8080. It returns the user that we have inserted in the database.

Spring Boot jpa

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    JPA annotations are used in mapping java objects to the database tables, columns etc. Hibernate is the most popular implement of JPA specification and provides some additional annotations. Today we will look into JPA annotations as well as Hibernate annotations with brief code snippets. JPA Annotations - Hibernate Annotations

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  6. JPA @Basic Annotation

    JPA Annotations 1. Overview In this quick tutorial, we'll explore the JPA @Basic annotation. We'll also discuss the difference between @Basic and @Column JPA annotations. 2. Basic Types JPA support various Java data types as persistable fields of an entity, often known as the basic types. A basic type maps directly to a column in the database.

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    JPA entities don't need to implement any interface or extend a superclass. They are simple POJOs. But you still need to identify a class as an entity class, and you might want to adapt the default table mapping. @Entity. The JPA specification requires the @Entity annotation. It identifies a class as an entity class. @Entity public class ...

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    We annotate the class with @Entity so that it can be included in the persistence unit. We do this because the "persistence context" only manages the instances of those set of classes that are contained within the persistence unit. In case of persistence.xml, we include the class in the persistence unit by the use of <class> tag.

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