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 animals = new          


        

Answer 1

I think you have to annotate the interface too with @Entity and we have to annotate @Transient on all getters and setters of interface.

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.

Answer 3

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