public async Task <IActionResult> Create(LessonDto lessonDto)
        {
            if (await _lessonService.AreThereLesson(lessonDto.LessonName.ToLower(), lessonDto.FkGradeId) == false)
            {
                await _lessonService.AddAsync(_mapper.Map <Lesson>(lessonDto));

                ViewBag.ErrorMessage = "";
                return(RedirectToAction("GetAll", "Lesson"));
            }
            ViewBag.ErrorMessage = "Sistemde aynı isme ait ders bulunmaktadır...!";
            return(View(lessonDto));
        }