Take a look at ejb3_0-pdf-spec-persistence.pdf, section 9.1.25... You could use MapKey annotation for that. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3982455#3982455 Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&p=3982455