Hello EveryOne, i've mapped many2many between user and skill tables ,when it is uni-directional works fine but the problem occurs when i made it to bi-directional. i've written many2many mapping in user class The following exception is thrown when i try to insert record. Caused by: java.sql.BatchUpdateException: ORA-01400: cannot insert NULL into ("SYSTEM"."CUSER_SKILL"."CUSER_USERID") CUSER_USERID(column) is getting created automatically in join table. thanks in advance. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4184485#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...