ModelState.AddModelError使用

后台：ModelState.AddModelError("userPwd", "请输入密码！");

ModelState是一个字典类型，这句话的作用是向ModelState中添加一条错误信息，第一个参数是Key,第二个参数是Value。


前台：Html.ValidationMessage(key) 或 Html.ValidationSummary() 来显示


对于什么时候使用ModelState.AddModelError（模型错误）的思考与总结：
针对马拉松赛事：
（1）当前的赛事是否存在

 var eventMessage = _eventSystemMessageService.GetAllEventSystemMessages().FirstOrDefault(x => x.EventName == currentEventName);  //查询出该条数据
                if (eventMessage == null)//判断是否存在
                {
                    string no_NowEvent = _localizationService.GetResource("Event.EventRegister.No_NowEvent");   //进行语言转换
                    ModelState.AddModelError("", no_NowEvent);//"不存在当前赛事"
                    InitRegisterModel(model);
                    return View(model);
                }

 var rms = _registratorMessageService.GetAllRegistratorMessages();  //所有数据

                var entity = rms.FirstOrDefault(r => r.RegistratorDocumentNumber == model.RegistratorDocumentNumber);//通过输入的数据与数据库的数据匹配得出一条数据
                if (entity != null)
                {
                    string hadDocumentNumber = _localizationService.GetResource("Event.EventRegister.HadDocumentNumber");
                    ModelState.AddModelError("", hadDocumentNumber);//"证件号码已存在"
                    InitRegisterModel(model);
                    return View(model);
                }

                var phoneValidEnity = rms.FirstOrDefault(r => r.RegistratorPhone == model.RegistratorPhone);//针对手机号查询数据
                if (phoneValidEnity != null)
                {
                    string hadPhoneNumber = _localizationService.GetResource("Event.EventRegister.PhoneNumber");
                    ModelState.AddModelError("", hadPhoneNumber);//"手机号码已存在"
                    InitRegisterModel(model);
                    return View(model);
                }

 var emailEntity = rms.FirstOrDefault(x => x.RegistratorEmail == model.RegistratorEmail);//通过邮箱查询匹配数据
                if (emailEntity != null)
                {
                    string yourEmailIsUsed = _localizationService.GetResource("Event.EventRegister.YourEmailIsUsed");
                    ModelState.AddModelError("", yourEmailIsUsed);//"该邮箱地址已被使用，请使用其他邮箱地址"
                    InitRegisterModel(model);
                    return View(model);
                }

  try
                {
                    Enmodel.RegistratorBirth = new DateTime(model.DateOfBirthYear, model.DateOfBirthMonth, model.DateOfBirthDay);
                }
                catch
                {
                   
                    string birthDayWrong = _localizationService.GetResource("Event.EventRegister.birthDayWrong");
                    ModelState.AddModelError("", birthDayWrong);// "生日输入不正确"
                    return