public IActionResult AddCourseStaff([FromBody] List <CourseStaffDto> courseStaffDto)
        {
            if (!ModelState.IsValid)
            {
                // return 422
                return(new Helpers.UnprocessableEntityObjectResult(ModelState));
            }

            try
            {
                // save
                var courseStaffFromRepo = _courseRepository.AddCourseStaff(courseStaffDto);

                var courseStaffToReturn = _mapper.Map <IEnumerable <CourseStaffDto> >(courseStaffFromRepo);

                return(Ok(courseStaffToReturn));
            }
            catch (AppException ex)
            {
                // return error message if there was an exception
                return(BadRequest(new { message = ex.Message }));
            }
        }