修改员工部门时 就保存错误
org.springframework.orm.hibernate4.HibernateSystemException: identifier of an instance of com.val.ssh.entities.Department was altered from 1 to 4; nested exception is org.hibernate.HibernateException: identifier of an instance of com.val.ssh.entities.Department was altered from 1 to 4
修改时如果id不为空就get员工
保存时 部门信息只有id改变了 ， 就保存错误了 
