DataServiceContext.AddLink(Object, String, Object) 方法

定義

命名空間:

System.Data.Services.Client

組件:

System.Data.Services.Client.dll

將指定的連結加入 DataServiceContext 正在追蹤的物件集。

public:
 void AddLink(System::Object ^ source, System::String ^ sourceProperty, System::Object ^ target);

public void AddLink (object source, string sourceProperty, object target);

member this.AddLink : obj * string * obj -> unit

Public Sub AddLink (source As Object, sourceProperty As String, target As Object)

參數

source

Object

新連結的來源物件。

sourceProperty

String

來源物件上傳回相關物件的導覽屬性名稱。

target

Object

透過新連結與來源物件相關的物件。

例外狀況

ArgumentNullException

當 source、sourceProperty 或 target 為 null 時。

InvalidOperationException

如果連結已存在。

-或-

如果 source 或 target 物件處於 Detached 或 Deleted 狀態。

-或-

如果 sourceProperty 不是集合。

範例

下列範例示範如何使用 AddLink 和 SetLink 方法來建立定義關聯性的連結。 此範例中也會明確設定 Order_Details 物件的導覽屬性。 此範例會DataServiceContext根據 Northwind 數據服務使用 Add Service Reference 工具所產生的 ，當您完成 WCF Data Services 時會建立此服務參考工具。

int productId = 25;
string customerId = "ALFKI";

Order_Detail newItem = null;

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);

try
{
    // Get the specific product.
    var selectedProduct = (from product in context.Products
                           where product.ProductID == productId
                           select product).Single();

    // Get the specific customer.
    var cust = (from customer in context.Customers.Expand("Orders")
                where customer.CustomerID == customerId
                select customer).Single();

    // Get the first order.
    Order order = cust.Orders.FirstOrDefault();

    // Create a new order detail for the specific product.
    newItem = Order_Detail.CreateOrder_Detail(
        order.OrderID, selectedProduct.ProductID, 10, 5, 0);

    // Add the new order detail to the context.
    context.AddToOrder_Details(newItem);

    // Add links for the one-to-many relationships.
    context.AddLink(order, "Order_Details", newItem);
    context.AddLink(selectedProduct, "Order_Details", newItem);

    // Add the new order detail to the collection, and
    // set the reference to the product.
    order.Order_Details.Add(newItem);
    newItem.Product = selectedProduct;

    // Send the changes to the data service.
    DataServiceResponse response = context.SaveChanges();

    // Enumerate the returned responses.
    foreach (ChangeOperationResponse change in response)
    {
        // Get the descriptor for the entity.
        EntityDescriptor descriptor = change.Descriptor as EntityDescriptor;

        if (descriptor != null)
        {
            if (descriptor.Entity.GetType() == typeof(Order_Detail))
            {
                Order_Detail addedItem = descriptor.Entity as Order_Detail;

                if (addedItem != null)
                {
                    Console.WriteLine("New {0} item added to order {1}.",
                        addedItem.Product.ProductName, addedItem.OrderID.ToString());
                }
            }
        }
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred when saving changes.", ex);
}

// Handle any errors that may occur during insert, such as
// a constraint violation.
catch (DataServiceRequestException ex)
{
    throw new ApplicationException(
        "An error occurred when saving changes.", ex);
}

Dim productId = 25
Dim customerId = "ALFKI"

Dim newItem As Order_Detail = Nothing

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

Try
    ' Get the specific product.
    Dim selectedProduct = (From product In context.Products _
                                           Where product.ProductID = productId _
                                           Select product).Single()

    ' Get the specific customer.
    Dim cust = (From customer In context.Customers.Expand("Orders") _
                Where customer.CustomerID = customerId _
                Select customer).Single()

    ' Get the first order. 
    Dim order = cust.Orders.FirstOrDefault()

    ' Create a new order detail for the specific product.
    newItem = Order_Detail.CreateOrder_Detail( _
    order.OrderID, selectedProduct.ProductID, 10, 5, 0)

    ' Add the new order detail to the context.
    context.AddToOrder_Details(newItem)

    ' Add links for the one-to-many relationships.
    context.AddLink(order, "Order_Details", newItem)
    context.AddLink(selectedProduct, "Order_Details", newItem)

    ' Add the new order detail to the collection, and
    ' set the reference to the product.
    order.Order_Details.Add(newItem)
    newItem.Product = selectedProduct

    ' Send the insert to the data service.
    Dim response As DataServiceResponse = context.SaveChanges()

    ' Enumerate the returned responses.
    For Each change As ChangeOperationResponse In response
        ' Get the descriptor for the entity.
        Dim descriptor = TryCast(change.Descriptor, EntityDescriptor)

        If Not descriptor Is Nothing Then

            Dim addedProduct = TryCast(descriptor.Entity, Product)

            If Not addedProduct Is Nothing Then
                Console.WriteLine("New product added with ID {0}.", _
                    addedProduct.ProductID)
            End If
        End If
    Next
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred when saving changes.", ex)

    ' Handle any errors that may occur during insert, such as 
    ' a constraint violation.
Catch ex As DataServiceRequestException
    Throw New ApplicationException( _
            "An error occurred when saving changes.", ex)

備註

通知 DataServiceContext 相關來源與目標物件之間有新連結，而且連結是以指定的來源屬性表示。 DataServiceContext 會將這個連結加入新建立的連結集，而在對 SaveChanges 的下一個呼叫時便會將該連結集傳送至資料服務。

連結是單向關聯性。 由於關聯是雙向的，因此在一對一關聯中，您必須再次呼叫來 AddLink 建立反向連結，而且在多對一關聯中，您必須呼叫 SetLink 來建立關聯「一」結尾的參考連結。

目標物件必須是 sourceProperty 參數所識別的型別，或是該型別的子型別。