OK, so I can use an Hibernate extension to workaround the issue. I see that the Hibernate doc says that merge() behaves this way (http://www.hibernate.org/hib_docs/entitymanager/reference/en/html_single/...), but where can I found the EJB3 spec stating this should be the behaviour of merge()? I can't find that being covered in the Sun doc. It would be nice if the EJB3 spec provided a way of avoiding this inefficiency. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3991837#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...