Thanks for the advice. However, the problem is that those columns are out of scope for any annotations I place on my columns. That's because those columns are automatically generated by hibernate to keep track of the OneToMany relationships. In other words I have no column on which I could place this annotation - because I don't define them (Only indirectly versus the OneToMany annotation). Hibernate should realize byitself that only ONE of those columns should be set per row and that the other columns should be set to NULL. Any other ideas? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4084057#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...