anonymous wrote : 1. is not possible this is not how you would work in a object model (wo persistence) But how can I provide reference integrity? If placeOfWork cannot be set to null automatically then it is possible to have references to non-existence objects. Especially in MySql database with MyISAM engine which does not support foreign keys... View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3972810#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...