/** 查询无班级学生信息 */
 @Override
 public List<StudentManagerDTO> queryStudentsWithoutClassId(String schoolId) {
   List<MStudentManager> usersList = studentMapper.selectStudentsWithoutClassId(null, schoolId);
   List<StudentManagerDTO> userDTOList = new ArrayList<>();
   for (MStudentManager user : usersList) {
     StudentManagerDTO userDTO = new StudentManagerDTO();
     BeanUtils.copyProperties(user, userDTO);
     userDTOList.add(userDTO);
   }
   return userDTOList;
 }