JPA annotations are not supported on interfaces. From Java Persistence with Hibernate (p.210):
Note that the JPA specification
doesn’t support any mapping annotation
on an interface! This will be resolved
in a future version of the
specification; when you read this
book, it will probably be possible
with Hibernate Annotations.
A possible solution would be to use an abstract Entity with a TABLE_PER_CLASS
inheritance strategy (because you can’t use a mapped superclass – which is not an entity – in associations). Something like this:
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractAnimal {
@Id @GeneratedValue(strategy = GenerationType.TABLE)
private Long id;
...
}
@Entity
public class Lion extends AbstractAnimal implements Animal {
...
}
@Entity
public class Tiger extends AbstractAnimal implements Animal {
...
}
@Entity
public class Zoo {
@Id @GeneratedValue
private Long id;
@OneToMany(targetEntity = AbstractAnimal.class)
private Set<Animal> animals = new HashSet<Animal>();
...
}
But there is not much advantages in keeping the interface IMO (and actually, I think persistent classes should be concrete).
References
- Annotations, inheritance and interfaces
- using MappedSuperclass in relation one to many
- Polymorphic association to a MappedSuperclass throws exception