public ActionResult PickGroupForHomework(PickGroupForHomeworkViewModel model)
        {
            ClassDeclarationsDBEntities6 entities = new ClassDeclarationsDBEntities6();
            //model.groups = entities.Groups.ToList();
            model.users = entities.Users.ToList();
            int id = model.subject_id;
            var subj = entities.Subjects
                    .Where(b => b.class_id == model.subject_id)
                    .FirstOrDefault();
            int j = 0;
            model.groups = new List<Group>();
            foreach(var group in entities.Groups)
            {
                if(group.class_id==model.subject_id)
                {
                    model.groups.Add(group);
                    j++;
                }
            }
            if (subj != null)
            {
                model.subject_name = subj.name;
            }
            if (ModelState.IsValid)
            {
                DateTime myDate = DateTime.ParseExact(model.deadline+ " "+model.time, "yyyy-MM-dd HH:mm",
                                       System.Globalization.CultureInfo.InvariantCulture);
                ClassDeclarationsDBEntities6 entities2 = new ClassDeclarationsDBEntities6();
                int total = entities2.Tasks.Count();
                string nameAndLocation = "~/UploadedFiles/" + model.file.FileName;
                model.file.SaveAs(Server.MapPath(nameAndLocation));
                for (int i=0;i<model.task_names.Count;i++)
                {
                    ClassDeclarationsDBEntities6 entities3 = new ClassDeclarationsDBEntities6();
                    int maxid;
                    if (total == 0)
                    {
                        maxid = 0;
                    }
                    else {
                        maxid = entities3.Tasks.Max(u => u.task_id);
                    }

                    var task = new Models.Task(model.task_names[i], model.subject_id, myDate, model.points[i], maxid + 1, nameAndLocation);
                    entities3.Tasks.Add(task);
                    entities3.SaveChangesAsync();
                }
                return RedirectToAction("OperationSuccess", "Account");
            }
            else
            {
                RedirectToAction("SetHomework", "Account");
                return View(model);
            }
            return View(model);

        }