Hiya. Because you're specifying: Debtor deb1 = new Debtor(); | deb1.setId(1); ...the entity manager will see this as "detached" - in other words, an object that is already persisted in the database (because it has a primary key), but is not currently managed by the entity manager. The "persist" method is used to perform an SQL Insert for a *new* object; one without a PK. So you can either: 1) Use EntityManager.merge() to synchronize these values with the database 2) Don't specify a PK; don't set the ID. ...depending on your PK Generation strategy. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3969774#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...