C# 使用（ling到sql）更新错误

我有两个表，由外键CarrierID绑定：

Carrier[CarrierID,CarrierName] 
CarrierID = 1, CarrierName = DHL
CarrierID = 2, CarrierName = Fedex
...
Vendor[VendorID, VendorName, CarrierID]  
VendorID = 1, VendorName =D-link , CarrierID=1  
VendorID = 2, VendorName = Netbes , CarrierID= 2

当我尝试在vendorview中更新carriername时。我收到这个错误“ForeignKeyReferenceAlreadyHasValueException”

我有一门叫做editvendor的课

public static void editvendor(Vendor vendor)
        {

            using (MyinvoiceDataDataContext connv = new MyinvoiceDataDataContext())
            {

                Vendor editven = (from s in connv.Vendors
                                 where s.VendorID == vendor.VendorID
                                 select s).FirstOrDefault();

                editven.VendorAddress = editven.VendorAddress;
                editven.VendorBalance = editven.VendorBalance;
                editven.VendorContactName = editven.VendorContactName;
                editven.VendorEmail = editven.VendorEmail;
                editven.VendorFax = editven.VendorFax;
                editven.VendorName = editven.VendorName;
                editven.VendorPaymentTerms = editven.VendorPaymentTerms;
                editven.VendorPhone = editven.VendorPhone;
                editven.VendorRemark = editven.VendorRemark;
                editven.VendorTax = editven.VendorTax;
                editven.VendorWebsite = editven.VendorWebsite;
                editven.CarrierID = editven.Carrier.CarrierID;
                connv.SubmitChanges();

            }
        }
        #endregion

在windows窗体（编辑供应商窗体）中，我使用以下命令：

 private void Window_Loaded(object sender, RoutedEventArgs e)
        {

            MyinvoiceDataDataContext contecta = new MyinvoiceDataDataContext();
            var tb = from s in contecta.Carriers
                     select new { s.CarrierID, s.CarrierName };
            comVendorCarrier.ItemsSource = tb;
            comVendorCarrier.DisplayMemberPath = "CarrierName";
            comVendorCarrier.SelectedValuePath = "CarrierID";

            ViewVendor vendview = new ViewVendor();
            txtVendorName.Text = vendor.VendorName.Trim();
            txtVendorBalance.Text = vendor.VendorBalance.Trim();
            txtVendorContactName.Text = vendor.VendorContactName.Trim();
            txtVendorPhone.Text = vendor.VendorPhone.Trim();
            txtVendorFax.Text = vendor.VendorTax.Trim();
            txtVendorEmail.Text = vendor.VendorEmail.Trim();
            txtVendorWebsite.Text = vendor.VendorWebsite.Trim();
            txtVendorRemarks.Text = vendor.VendorRemark.Trim();
            txtVendorAddress.Text = vendor.VendorAddress.Trim();
            txtVendorTax.Text = vendor.VendorTax.Trim();
            comVendorCarrier.Text = vendor.Carrier.CarrierName.Trim();
            ComVendorPaymentTerms.Text = vendor.VendorPaymentTerms.Trim();
        }

此代码用于保存已编辑的供应商

 private void EditVendorSavebtn_Click_1(object sender, RoutedEventArgs e)
        {
            int SelectedCarrierId = int.Parse(comVendorCarrier.SelectedValue.ToString());
            if (txtVendorName.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's Name");

            if (txtVendorBalance.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's balance");

            if (txtVendorContactName.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's contact name");

            if (txtVendorPhone.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's phone number");

            if (txtVendorFax.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's fax number");

            if (txtVendorEmail.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's E-maill");

            if (txtVendorWebsite.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's Website");

            if (txtVendorAddress.Text.Trim() == "")
                MessageBox.Show("Please fill vendor's address");

            else
            {

                vendor.VendorName = txtVendorName.Text.Trim();
                vendor.VendorBalance = txtVendorBalance.Text.Trim();
                vendor.VendorContactName = txtVendorContactName.Text.Trim();
                vendor.VendorPhone = txtVendorPhone.Text.Trim();
                vendor.VendorFax = txtVendorFax.Text.Trim();
                vendor.VendorEmail = txtVendorEmail.Text.Trim();
                vendor.VendorWebsite = txtVendorWebsite.Text.Trim();
                vendor.VendorRemark = txtVendorRemarks.Text.Trim();
                vendor.VendorAddress = txtVendorAddress.Text.Trim();
                vendor.VendorPaymentTerms = ComVendorPaymentTerms.Text;
                vendor.CarrierID = SelectedCarrierId;
                vendor.VendorTax = txtVendorFax.Text.Trim();
                vendorinfo.editvendor(vendor);
                MessageBox.Show(vendor.VendorName + " succesfully edited.");
                Window_Loaded(null, null);
            }

---

我希望是这样的组合：

// somewhere
comVendorCarrier.Text = vendor.Carrier.CarrierName.Trim();
...
// somewhere else
vendor.CarrierID = SelectedCarrierId;

一种是使用面向对象的方法，另一种是使用基于id的方法-但是，如果两者都加载且不兼容，则会出现问题。我想知道您是否应该使用：

vendor.Carrier = null;
vendor.CarrierID = SelectedCarrierId;

那么，使用哪种载体就只有一个定义

或者，单独处理载体，例如，而不是：

comVendorCarrier.Text = vendor.Carrier.CarrierName.Trim();

使用：

---

它永远不会将

vendor.Carrier

作为对象加载。

我还没有通读您的所有代码，但是您可以记住，使用Linq2SQL，您通常不需要自己设置任何ID，只需添加对对象实例的引用即可。因此，在您的情况下：

vendor.Carrier=Carrier

，其中

Carrier

是

Carrier

的一个实例，还将正确的

CarrierID

添加到

供应商

。不需要自己添加Id。请再次检查代码，因为'var carrier=context.Carriers.Single（x=>x.Id=vendor.CarrierId）；comVendorCarrier.Text=carrier.CarrierName.Trim（）；'不适合我。这里有问题'var carrier=context.Carriers.Single（x=>x.Id=vendor.CarrierId）；comVendorCarrier.Text=carrier.CarrierName.Trim（）；'找不到Id。@Thivakaransevarajoo，代码将无法编译，原因有二：1。你没有

x.Id

，但是

x.CarrierID

，正如我在你的问题和2中看到的那样。

=

（赋值）应该是

=

（等于）'var carrier=context.Carriers.Single（x=>x.CarrierID==vendor.CarrierID）`@Marc gravel，我仍然收到相同的错误“ForeignKeyReferenceAlreadyHasValueException”

var carrier  = context.Carriers.Single(x => x.Id = vendor.CarrierId);
comVendorCarrier.Text = carrier.CarrierName.Trim();