I have defined a collection in Hibernate like this:

...
public class Item {
    ...
    @ElementCollection
    List<Object> relatedObjects;
}

It creates a mapping table with colums item_id and object_id.

The problem is that object_id seems to be unique. In other words I can not have two different items being related to the same object. But that is what I want.

I would like the combination of item_id and object_id to be unique. How do I do that?