Persist collection of interface using Hibernate

Question

I want to persist my litte zoo with Hibernate:

@Entity @Table(name = "zoo")  public class Zoo {     @OneToMany     private Set<Animal> animals = new HashSet<Animal>(); }  // Just a marker interface public interface Animal { }  @Entity @Table(name = "dog") public class Dog implements Animal {     // ID and other properties }  @Entity @Table(name = "cat") public class Cat implements Animal {     // ID and other properties } 

When I try to persist the zoo, Hibernate complains:

Use of @OneToMany or @ManyToMany targeting an unmapped class: blubb.Zoo.animals[blubb.Animal] 

I know about the targetEntity-property of @OneToMany but that would mean, only Dogs OR Cats can live in my zoo.

Is there any way to persist a collection of an interface, which has several implementations, with Hibernate?

Answer 1

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

Answer 2

I can guess that what you want is mapping of inheritance tree. @Inheritance annotation is the way to go. I don't know if it will work with interfaces, but it will definitely work with abstract classes.