Room r = this.findByStudentNum(studentNum); if(r!=null){ map.put("oldRoomNum", r.getRoomNum()); }else{ map.put("oldRoomNum","无"); }
	public void updateStudentRoom(String studentNum, int roomId) {		Map<String,Object> map = new HashMap<String,Object>();		map.put("studentNum", studentNum);		map.put("roomId", roomId);		getSqlSession().update(Room.class.getName()+".update_student_room_id",map);	}