public async Task <ActionResult> EditGrade(GradeEditViewModel model)
        {
            if (ModelState.IsValid)
            {
                var grade = await InstitutionManager.FindGradeByIdAsync(model.Id);

                if (grade == null)
                {
                    ModelState.AddModelError("", "未找到此项grade");
                    return(View(model));
                }
                grade.GradeNum = model.GradeNumber;
                await InstitutionManager.UpdateGradeAsync(grade);

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