public Result AssignClass(int teacherId, int classId)
        {
            Class c = null;

            if (_teacherGateway.FindById(teacherId) == null)
            {
                return(Result.Failure(Status.BadRequest, "Unknown teacher."));
            }
            if (classId != 0 && (c = _classGateway.FindById(classId)) == null)
            {
                return(Result.Failure(Status.BadRequest, "Unknown class."));
            }
            if (c != null && c.TeacherId != 0 && c.TeacherId != teacherId)
            {
                return(Result.Failure(Status.BadRequest, "Class already assigned."));
            }
            _teacherGateway.AssignClass(teacherId, classId);
            return(Result.Success(Status.Ok));
        }
        public async Task <IActionResult> AssignClass(int id, [FromBody] AssignClassViewModel model)
        {
            Result result = await _teacherGateway.AssignClass(id, model.ClassId);

            return(this.CreateResult(result));
        }