I recently put this in the EJB forum and later discovered that this is where it should be: I am trying to develop a entity which extends another entity and which use the annotation @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS), but this only provides an exception as the sub class does not have an @Id annotated: org.hibernate.MappingException: Cannot use identity column key generation with <union-subclass> mapping for: concept.entity.Entity However: If I do annotate this @Id, I get this one: org.hibernate.AnnotationException: Unable to define/override @Id(s) on a subclass: concept.entity.En | tity Suggestions? I had the idea that @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) would give a new table with every field from the sub classes and mother class in this table. I searched the final draft on persistence for this notation but I came up with no suitable instances found. Is this assumption of the strategy correct or (especially since this is not working) is it another way of doing this? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3959842#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...