DataServiceContext.SetLink(Object, String, Object) 方法

定義

命名空間:

System.Data.Services.Client

組件:

System.Data.Services.Client.dll

通知 DataServiceContext，來源和指定的目標物件之間存在新連結，以及由 sourceProperty 參數所指定的屬性表示該連結。

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

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

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

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

參數

source

Object

新連結的來源物件。

sourceProperty

String

來源物件上的屬性名稱，識別新連結的目標物件。

target

Object

新連結中所含有的子物件，這個連結要透過呼叫此方法進行初始化。 目標物件必須是 sourceProperty 參數所識別之型別的子型別。 如果 target 是設為 null，則這個呼叫表示刪除連結作業。

例外狀況

ArgumentNullException

當 source、sourceProperty 或 target 為 null 時。

InvalidOperationException

指定的連結已經存在。

-或-

提供為 source 或 target 的物件處於 Detached 或 Deleted 狀態。

-或-

sourceProperty 不是定義單一相關對象的參考的導覽屬性。

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。

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

新連結是以 Added 狀態建立。 DataServiceContext 會將這個新連結加入至要在新建立的連結集，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。

如果 target 引數為 null，則應該移除或刪除 sourceProperty 所表示的連結 (其狀態會進入 Deleted 狀態)。

連結是單向關聯性。 如果後端指標存在，表示雙向關聯，則應該再次呼叫此方法，以通知 DataServiceContext 第二個連結的

這個方法只支援將連結加入重數為 1 的關聯性 (來源屬性是物件參考)。 舉例來說，如果 Person 類別與另一個 Person 有 Friend 屬性的關係，這個呼叫可以用來使 Person 和 Person 產生關係。 如果 sourceProperty 代表有多個基數的關聯性，此方法會擲回例外狀況。