Hi, bi-directional mappings are a bit tricky: you always have to update BOTH sides of the mapping. So, if you want to map a Skill to an User, this will NOT work: user.getSkills().add ( mySkill); | entityManager.merge(user); You will have to do something like this: myUser.getSkills().add ( mySkill); | mySkill.getUsers().add (myUser); | entityManager.merge(myUser); Hope this helps Wolfgang View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4184503#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...