293 words

javax.persistence.EmbeddedId - JPA annotation

javax.persistence
Annotation EmbeddedId

Target:
Fields (including property get methods)
Applied to a persistent field or property of an entity class or mapped superclass to denote a composite primary key that is an embeddable class. The embeddable class must be annotated as Embeddable.

There must be only one EmbeddedId annotation and no Id annotation when the EmbeddedId annotation is used.

The AttributeOverride annotation may be used to override the column mappings declared within the embeddable class.

The MapsId annotation may be used in conjunction with the EmbeddedId annotation to specify a derived primary key.

If the entity has a derived primary key, the AttributeOverride annotation may only be used to override those attributes of the embedded id that do not correspond to the relationship to the parent entity.

Relationship mappings defined within an embedded id class are not supported.

Example 1:

    @EmbeddedId
    protected EmployeePK empPK;

Example 2:

    @Embeddable
    public class DependentId {
       String name;
       EmployeeId empPK;   // corresponds to primary key type of Employee
    }
 
    @Entity
    public class Dependent {
       // default column name for "name" attribute is overridden
       @AttributeOverride(name="name", @Column(name="dep_name"))
       @EmbeddedId DependentId id;
       ...
       @MapsId("empPK")
       @ManyToOne Employee emp;
    }

Since:
JPA 1.0
See Also:
Embeddable
MapsId
Learn how to define and use embedded ID fields in Chapter 2 of the ObjectDB/JPA manual.
This annotation is a marker annotation (with no elements).

This documentation page is derived (with some adjustments) from the open source JPA 2 RI (EclipseLink)
and is available under the terms of the Eclipse Public License, v. 1.0 and Eclipse Distribution License, v. 1.0.
Object Relational Mapping (ORM) JPA 2 providers include Hibernate, EclipseLink, TopLink, OpenJPA and DataNucleus.
Object DB is not an ORM JPA implementation but an Object Database for Java with built in JPA 2 support.