public async Task <ActionResult> CreateGrade(GradeCreateViewModel model)
        {
            if (ModelState.IsValid)
            {
                if (model.GradeNumber == 0)
                {
                    ModelState.AddModelError("", "GradeNumber不能为0");
                }
                else
                {
                    var grade = await InstitutionManager.FindGradeByGradeNumberAsync(model.GradeNumber);

                    if (grade == null)
                    {
                        await InstitutionManager.AddGradeAsync(model.GradeNumber);

                        return(RedirectToAction("AllGrade"));
                    }
                    else
                    {
                        ModelState.AddModelError("", "已有相同名称");
                    }
                }
            }
            return(View(model));
        }