What merge () does is - is to put back the detached entity back into persistence storage. So if in yr case- if yr entity was detached it will put it back to persistence which means you don't have to call persist again. For answer to part 2. - merge() method with throw an illegal Arguement Exception if its paramter is not an entity type. I hope this helps.... View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3974755#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...