a different object with the same identifier value was already associated with the session

a different object with the same identifier value was already associated with the session

出现异常的代码：

session.beginTransaction();   //开启事务

String hql="from MessageForm m where m.msg_id='"+msg_id+"'";
list=session.createQuery(hql).list();
MessageForm myform=(MessageForm)list.get(0);
myform.setMsg_back(msgform.getMsg_back());
myform.setMsg_back_time(msgform.getMsg_back_time());

session.update(myform);

session.getTransaction().commit();   //提交事务

修改后没问题的代码：

session.beginTransaction();   //开启事务

String hql="from MessageForm m where m.msg_id='"+msg_id+"'";
list=session.createQuery(hql).list();
MessageForm myform=(MessageForm)list.get(0);
myform.setMsg_back(msgform.getMsg_back());
myform.setMsg_back_time(msgform.getMsg_back_time());

session.update(myform);
session.save(myform);

session.getTransaction().commit();   //提交事务

参见：http://guoxubo.javaeye.com/blog/363019