public async Task <IActionResult> AddAbsence(int id, AddAbsenceViewModel model)
        {
            var currentUser = _context.Users.FirstOrDefault(u => u.UserName == User.Identity.Name);

            if (id != model.StudentClassroomId)
            {
                return(NotFound());
            }

            var studentClassroom = _context.StudentClassrooms
                                   .Include(s => s.Absences)
                                   .SingleOrDefault(s => s.Id == id);

            if (studentClassroom == null)
            {
                return(NotFound());
            }

            var absence = new Absence()
            {
                Description        = model.Description,
                AbsenceDate        = model.AbsenceDate,
                StudentClassroomId = model.StudentClassroomId,
                Student            = currentUser,
                LostLessons        = new List <Lesson>()
            };

            if (ModelState.IsValid)
            {
                try
                {
                    studentClassroom.Absences.Add(absence);
                    _context.Update(studentClassroom);
                    await _context.SaveChangesAsync();
                }
                catch (DbUpdateConcurrencyException)
                {
                    if (!StudentClassroomExists(studentClassroom.Id))
                    {
                        return(NotFound());
                    }
                    else
                    {
                        throw;
                    }
                }
                return(RedirectToAction(nameof(Index)));
            }
            return(View(model));
        }
        //GET: FrequencyAndMarks/Addabsence/5
        public async Task <IActionResult> AddAbsence(int?id)
        {
            var studentClassroom = await _context.StudentClassrooms.SingleOrDefaultAsync(m => m.Id == id);

            if (studentClassroom == null)
            {
                return(NotFound());
            }

            var model = new AddAbsenceViewModel()
            {
                StudentClassroomId = (int)id
            };

            return(View(model));
        }