public async Task <ActionResult> CreateClass(ClassCreateViewModel model)
        {
            var departments = await InstitutionManager.GetAllDepartmentsAsync();

            SelectList departSelectList = new SelectList(departments, "Id", "Name");

            ViewBag.departSelectList = departSelectList;

            var majors = await InstitutionManager.GetMajorsForDepartmentAsync(departments.ElementAtOrDefault(0));

            SelectList majorSelectList = new SelectList(majors, "Id", "Name");

            ViewBag.majorSelectList = majorSelectList;

            var grades = await InstitutionManager.GetAllGradesAsync();

            SelectList gradeSelectList = new SelectList(grades, "Id", "GradeNum");

            ViewBag.gradeSelectList = gradeSelectList;

            ViewBag.Classes = await InstitutionManager.GetAllClassesAsync();

            if (ModelState.IsValid)
            {
                var grade = await InstitutionManager.FindGradeByIdAsync(model.GradeId);

                if (grade == null)
                {
                    ModelState.AddModelError("", "找不到grade");
                    return(View(model));
                }
                var major = await InstitutionManager.FindMajorByIdAsync(model.MajorId);

                if (major == null)
                {
                    ModelState.AddModelError("", "找不到major");
                    return(View(model));
                }
                var class1 = new Class
                {
                    ClassDefination = model.Defination,
                    Grade           = grade,
                    Major           = major
                };
                if (await InstitutionManager.IsClassExistAsync(c =>
                                                               !c.IsDeleted && c.Grade.Id == class1.Grade.Id && c.Major.Id == class1.Major.Id &&
                                                               c.ClassDefination == class1.ClassDefination))
                {
                    ModelState.AddModelError("", "已存在Class");
                    return(View(model));
                }
                await InstitutionManager.AddClassAsync(class1);

                return(RedirectToAction("AllClass"));
            }
            return(View(model));
        }