执行 linq 查询时，它会抛出转换错误 system.int32

Question

var Appointment = (from app in _context.Appointments
                                   join pt in _context.Patients on app.PatientID equals pt.ID into 
                                   patients
                                   from pt in patients.DefaultIfEmpty()
                                   join doc in _context.Doctors on app.DoctorID equals doc.ID into 
                                   doctors
                                   from doc in doctors.DefaultIfEmpty()
                                       //join offloc in _context.OfficeLocations on app.DoctorID 
                                    equals offloc.DoctorID into officlocation
                                       //from offloc in officlocation.DefaultIfEmpty()
                                   join docavail in _context.DoctorsAvailabilities on 
                                   app.AvailabilityID equals docavail.ID into availability
                                   from docavail in availability.DefaultIfEmpty()
                                   where ((app.CreatedByReferral == ReferralSpecialistID || 
                                   app.CompanyID == CompanyID || app.UserGroupID == CompanyID) && 
                                   app.OtherPatientID == null && pt.Status == StatusConstant.Active 
                                   && app.Status != AppointmentRescheduledID && 
                                   app.IsCloseAppointment != true)
                                   select new AppointmentDataTableResult
                                   {

                                       appointmentID = app.ID,
                                       PatientID = pt.ID,
                                       patientname = (pt.NamePrefix ?? "") + " " + pt.FirstName + " " + pt.LastName + " " + (pt.NameSuffix ?? ""),
                                       ParentPatientID = 0,
                                       dateofbirth = pt.DateOfBirth,
                                       patientType = _context.CategoryDetails.Where(x => x.ItemID == app.PatientTypeID).Select(x => x.MasterData).FirstOrDefault(),
                                       phone = pt.Phone,
                                       Date = docavail.Date,
                                       Time = docavail.Time,
                                       statustext = _context.CategoryDetails.Where(x => x.ItemID == app.Status).Select(x => x.MasterData).FirstOrDefault(),
                                       doctorname = (doc.NamePrefix ?? "") + " " + doc.FirstName + " " + doc.LastName + " " + (doc.NameSuffix ?? ""),
                                       DoctorID = doc.ID,
                                       checkin = app.CheckIn,
                                       checkout = app.CheckOut,
                                       checkintime = app.CheckInTime,
                                       checkouttime = app.CheckOutTime,
                                       withoutslot = app.WithoutSlot,
                                       locatioid = app.LocationID ?? 0,
                                       AppointmentSource = app.AppointmentSource ?? 0,
                                       Status = app.Status ?? 0,
                                       IsPastAppointment = app.IsPastAppointment,
                                       casestatusID = app.CaseStatusID ?? 0,
                                       caseTypeID = app.CaseTypeID ?? 0,
                                       ReferralAttorneyID = app.ReferralAttorneyID ?? 0,
                                       ReferralProviderID = app.ReferralProviderID ?? 0,
                                       patientTypeID = app.PatientTypeID ?? 0,
                                       InsuranceID = app.InsuranceID ?? 0,
                                       PendingAppointmentDate = app.PreferredAppointmentDateTime,
                                       // AppointmentDate = docavail.Date.Value.Month + "/" + docavail.Date.Value.Day + "/" + docavail.Date.Value.Year + " " + docavail.Time.Value.Hours + ":" + docavail.Time.Value.Minutes,
                                       ReportCount = _context.DoctorReportStatus.Where(x => x.StatusID == StatusConstant.Active && x.AppointmentID == app.ID).Count(),
                                       RerecordUploadedYN = app.RerecordUploadedYN,
                                       IsAppointmentPending = app.IsAppointmentPending,
                                       IsPendingBillingRecoardYN = app.IsPendingBillingRecoardYN,
                                       strDate = docavail.Date.Value.Month + "/" + docavail.Date.Value.Day + "/" + docavail.Date.Value.Year,
                                       DateChekin = default(DateTime),
                                       totaldays = 0
                                   });

Answer 1

我也经常遇到同样的问题，当您放置 Tolist 方法时会出现此问题，因为在放置 Tolist() 方法之前，查询生成的输出属于类型
可查询
但这不是您问题的解决方案

问题是可能是 1 您将 Nullable 整数类型变量分配给不可为 null 的整数类型值或 2 将 Nullable 整数值与 Join 中的 Non Nullable 值进行比较，反之亦然

第二种情况的机会更大，因为在分配时，c#编译器会出错 检查您的比较变量类型，让我进行一些跟进。