EclipseLink entity mapping problem when using prop

Question

Given the class below does anyone know why EclipseLink implementation of JPA fails to map them to database entities? The following error is returned:

Entity class [class com.my.entity.Y] has no primary key specified. It should define either an @Id, @EmbeddedId or an @IdClass. If you have defined PK using any of these annotations then make sure that you do not have mixed access-type (both fields and properties annotated) in your entity class hierarchy.

@Entity
@Access(AccessType.PROPERTY)
public interface Y {

    void setId(Long id);

    @Id
    Long getId();
}

@Entity
public class Z implements Y {

    long id;

    @Override
    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public Long getId() {
        return id;
    }
}

Many thanks

Answer 1

Thanks to the person who linked to this question - it helped me come up with a solution to the issue as follows:

    @Entity
    public interface Y {

        void setId(Long id);

        @Id
        Long getId();
    }

   // introduce intermediate abstract class which implements Y

    @Entity
    public abstract class X implements Y {

    }

    // make Z extends X

    @Entity
    public class Z  extends X {

        // use targetEntity = X.class where required
        // leaving this class still free to use interface Y

        long id;

        @Override
        public void setId(Long id) {
            this.id = id;
        }

        @Override
        public Long getId() {
            return id;
        }
    }

Answer 2

You cannot annotate or query on an inferface. You can only query @Entity classes, and these can only be placed on real classes, not interfaces. Use the @MappedSuperclass annotation for inheritance.

See these: http://download.oracle.com/javaee/6/tutorial/doc/bnbqn.html#bnbqp and JPA doesn't support interfaces well..implications?

Answer 3

EclipseLink does support querying and relationships to interfaces, but not currently in annotations.

To map the interface you can use a SessionCustomizer.

public class MyCustomizer implements SessionCustomizer {
    public void customize(Session session) {
      RelationalDescriptor descriptor = new RelationalDescriptor();
      descriptor.setJavaInterface(Y.class);
      descriptor.setAlias("Y");
      session.addDescriptor(descriptor);
    }
}

Mapping the interface allows querying on the interface which returns any of its subclasses, and defining relationships to the interface.

If the interface is used through the @VariableOneToOne annotation it will be automatically mapped.