By further probing my code, I found it is actually caused by em.clear at another component. i.e. when I select a row at dataTable, the following code is executed: | InvoiceContacts invoiceContactsAction = (InvoiceContacts) Component.getInstance("invoiceContactsAction", | ScopeType.SESSION); | invoiceContactsAction.changeInvoice(getSelectedInvoice()); | And code at component invoiceContactsAction is below: | @Stateful | @Name("invoiceContactsAction") | @Scope(ScopeType.SESSION) | public class InvoiceContactsAction implements InvoiceContacts { | | @PersistenceContext | EntityManager em; | | ... | | public void changeInvoice(Invoice selectedInvoice) { | this.selectedInvoice = selectedInvoice; | tempList = null; | invContacts = null; | em.clear(); | } | | ... | } | So the question turn out to be: Why does clearing the entity manager at a component make the entity bean retrieved by another component detached under this situation? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4004664#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...