Composite Primary Key Handling with JPA

Data versioning requires the ability to duplicate an entity with different versions, making it essential to create a composite primary key for entities.

Entity Definition with Composite Primary Key

In JPA, composite primary keys can be defined using either the @EmbeddedId or @IdClass annotations.

Using @EmbeddedId

Define a separate class (@Embeddable annotated) for the key, and then annotate it with @EmbeddedId in the entity:

@Entity
public class YourEntity {
    @EmbeddedId
    private MyKey myKey;

    private String columnA;
    // getters and setters
}

@Embeddable
public class MyKey implements Serializable {

    private int id;
    private int version;
    // getters and setters
}

Using @IdClass

Alternatively, annotate the class with @IdClass and define the ID attributes as @Id within the class:

@Entity
@IdClass(MyKey.class)
public class YourEntity {

    @Id
    private int id;

    @Id
    private int version;

}

public class MyKey implements Serializable {
   private int id;
   private int version;
}

Duplicating Entities with Versions

Once the entity is defined, it can be duplicated with a new version. For example, to create a new version of the first entity with id=1:

YourEntity newVersion = new YourEntity();
newVersion.setMyKey(new MyKey(1, 1)); // new version
newVersion.setColumnA("Some Other Data");
entityManager.persist(newVersion);