Sorry, it seems we are experiencing a language barrier :( I didn't fully understand what you just said.

I understood: in HBM an interface may be subclassed by multiple classes but may have only one superclass. This is different in an annotation approach. Please correct me if I misunderstood.

Thing is, are you telling me that even without annotations, it is impossible to represent a class that implements multiple interfaces? That is, Hibernate only allows a single "implements" or "extends" statement per class? This would be problematic :(

As well, why is this different in annotations? Do they say we should be supporting this?

Thank you,
Gili

In association declaration ie targetEntity, you have to declare a *mapped* class/interface.
In Hibernate a mapped class can only have 1 single mapped superclass or interface.

There is no extends nor implements restriction of any kind.

If I understand you correctly, you are saying I wouldn't be able to map the following inheritance in Hibernate even if I wasn't using Annotations:

interface Animal
{
public String getName();
}

interface Talks
{
public void talk();
}

class Dog implements Animal, Talks
{
Set<Dog> getFriends()
{
// body
}

// Implement getName(), talk()
}

Doesn't this imply that "ideally" we'd want Hibernate to support mapped classes implementing multiple interfaces? That is, this is not an annotation problem but rather one in Hibernate core?

Gili

Of course you can do that, both in hbm and annotations.

What you cannot do is



ie set 2 super classes/interfaces for Dog.
Only mapped interfaces can be used as *explicit implementations* in Hibernate collections declaration (ie in the hbm file not the java class), eg


This bag will be able to get all declared subclasses of Animals (Dog in our example).

The discussion took place in 2005, has anything changed since?

Is it allowed to do this :

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public interface Animal {}

@Entity
@DiscriminatorValue("Dog")
public class Dog implements Animal

Animal is mapped to the database, but "InheritanceType.SINGLE_TABLE" isn't taken into account so I have 2 tables: Animal and Dog. What am I doing wrong?