DataServiceContext.SetLink(Object, String, Object) 方法

定义

命名空间:

System.Data.Services.Client

程序集:

System.Data.Services.Client.dll

通知 DataServiceContext，说明指定的对象之间存在新链接，且该链接由 sourceProperty 参数指定的属性表示。

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)

参数

source

Object

新链接的源对象。

sourceProperty

String

源对象上的属性，用于标识新链接的目标对象。

target

Object

新链接中涉及的子对象，可通过调用此方法进行初始化。 目标对象必须是 sourceProperty 参数标识的类型的子类型。 如果 target 设置为 null，则调用表示删除链接操作。

例外

ArgumentNullException

当 source、sourceProperty 或 target 为 null 时。

InvalidOperationException

指定的链接已存在。

-或-

作为 source 或 target 提供的对象处于 Detached 或 Deleted 状态。

-或-

sourceProperty 不是定义对单个相关对象的引用的导航属性。

示例

以下示例演示如何使用 AddLink 和 SetLink 方法来创建用于定义关系的链接。 在此示例中，还显式设置了 Order_Details 对象的导航属性。

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)

注解

在 Added 状态下创建了新链接。 DataServiceContext 将此新链接添加到新创建的链接集，下次调用 SaveChanges 时，会将该链接集发送到数据服务。

如果目标自变量为 null，则应移除或删除由 sourceProperty 表示的链接（将该链接转为 Deleted 状态）。

链接是单向关系。 如果存在指示双向关联的后退指针，则应再次调用此方法以通知 DataServiceContext 第二个链接的

此方法仅支持将链接添加到多重性为 1 的关系（源属性为对象引用）。 例如，如果类 Person 通过 Person 属性与另一 Friend 类相关联，则此调用可用于将 Person 与 Person 进行关联。 如果所代表的 sourceProperty 具有多基数关系，则此方法将引发异常。