Question

我要更新用户记录后，当我按“更新”按钮时，我得到

An unhandled exception occurred while processing the request.
ArgumentNullException: Value cannot be null.
Parameter name: source
System.Linq.Enumerable.Select<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector)

这是我更新用户记录的功能：

 [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Edit(int id, AppointmentDetailsViewModel objAppointmentVM)
        {
            if(ModelState.IsValid)
            {
                objAppointmentVM.Appointment.AppointmentDate = objAppointmentVM.Appointment.AppointmentDate
                    .AddHours(objAppointmentVM.Appointment.AppointmentTime.Hour)
                    .AddMinutes(objAppointmentVM.Appointment.AppointmentTime.Minute);

                var appointmentFromDb = _db.Appointments.Where(a => a.Id == objAppointmentVM.Appointment.Id).FirstOrDefault();

                appointmentFromDb.CustomerName = objAppointmentVM.Appointment.CustomerName;
                appointmentFromDb.CustomerEmail = objAppointmentVM.Appointment.CustomerEmail;
                appointmentFromDb.CustomerPhoneNumber = objAppointmentVM.Appointment.CustomerPhoneNumber;
                appointmentFromDb.AppointmentDate = objAppointmentVM.Appointment.AppointmentDate;
                appointmentFromDb.isConfirmed = objAppointmentVM.Appointment.isConfirmed;

                if(User.IsInRole(SD.SuperAdminEndUser))
                {
                    appointmentFromDb.SalesPersonId = objAppointmentVM.Appointment.SalesPersonId;
                }

                _db.SaveChanges();
                return RedirectToAction(nameof(Index));
            }
            return View(objAppointmentVM);
        }

此功能适用于下拉菜单，可显示来自数据库的用户

public static IEnumerable<SelectListItem> ToSelectListItemString<T>(this IEnumerable<T> items, string selectedValue)
        {
            if(selectedValue == null)
            {
                selectedValue = "";
            }
            return from item in items
                   select new SelectListItem
                   {
                       Text = item.GetPropertyValue("Name"),
                       Value = item.GetPropertyValue("Id"),
                       Selected = item.GetPropertyValue("Id").Equals(selectedValue.ToString())
                   };
        }

任何想法我弄错了吗？

Answer 1

也许您表的列设置为not null。

转到SQL Server并打开表。在设计表窗口中，选中allow nulls复选框。

Answer 2

在您的项目中，选择其中一项为null，并且LINQ未能引发参数异常，因为您试图在null值上运行选择器函数。

尝试更新记录后，我得到“值不能为空”

2 个答案: