public IActionResult GetAllUsers(int classId)
        {
            // Assume the user is not authorized
            IActionResult result = Unauthorized();

            try
            {
                var users  = _db.GetUsersByClassId(classId);
                var dtoArr = users.Select(x => MapToDTO(x)).ToArray();
                result = Ok(dtoArr);
            }
            catch (Exception)
            {
                result = BadRequest(new { Message = "Get all users failed." });
            }

            return(result);
        }