HOW TO：使用 EntityReference 變更物件間的關聯性 (Entity Framework)

本主題示範如何使用 EntityReference 物件來變更物件內容中兩個物件之間的關聯性。 呼叫 SaveChanges 方法時，關聯性變更會做為關聯資料表內外部索引鍵的變更，保存在資料庫中。 如需詳細資訊，請參閱 HOW TO：在關聯變更期間執行商務邏輯。

本主題的範例根據 Adventure Works Sales Model。若要執行此主題中的程式碼，您必須已經將 Adventure Works Sales Model 加入到專案中，並設定您的專案使用 Entity Framework。如需詳細資訊，請參閱 HOW TO：使用實體資料模型精靈 (Entity Framework) 或 HOW TO：手動設定 Entity Framework 專案及 HOW TO：手動設定 Entity Framework 專案。

範例

本範例將示範如何使用 EntityReference 物件來變更 SalesOrderHeader 物件與代表訂單送貨地址之相關 Address 物件間的關聯性。

' Define the order and new address IDs. 
Dim orderId As Integer = 43669
Dim addressId As Integer = 26

Using context As New AdventureWorksEntities()
    ' Get the billing address to change to. 
    Dim address As Address = context.Addresses.Single(Function(c) c.AddressID = addressId)

    ' Get the order being changed. 
    Dim order As SalesOrderHeader = context.SalesOrderHeaders.Single(Function(o) o.SalesOrderID = orderId)

    ' You do not have to call the Load method to load the addresses for the order, 
    ' because lazy loading is set to true 
    ' by the constructor of the AdventureWorksEntities object. 
    ' With lazy loading set to true the related objects are loaded when 
    ' you access the navigation property. In this case Address. 

    ' Write the current billing street address. 
    Console.WriteLine("Current street: " & order.Address.AddressLine1)

    ' Change the billing address. 
    If Not order.Address.Equals(address) Then
        ' Use Address navigation property to change the association. 
        order.Address = address

        ' Write the changed billing street address. 
        Console.WriteLine("Changed street: " & order.Address.AddressLine1)
    End If

    ' If the address change succeeds, save the changes. 
    context.SaveChanges()

    ' Write the current billing street address. 
    Console.WriteLine("Current street: " & order.Address.AddressLine1)
End Using

// Define the order and new address IDs.
int orderId = 43669;
int addressId = 26;

using (AdventureWorksEntities context
    = new AdventureWorksEntities())
{
    // Get the billing address to change to.
    Address address =
        context.Addresses.Single(c => c.AddressID == addressId);

    // Get the order being changed.
    SalesOrderHeader order =
        context.SalesOrderHeaders.Single(o => o.SalesOrderID == orderId);

    // You do not have to call the Load method to load the addresses for the order,
    // because  lazy loading is set to true 
    // by the constructor of the AdventureWorksEntities object. 
    // With  lazy loading set to true the related objects are loaded when
    // you access the navigation property. In this case Address.

    // Write the current billing street address.
    Console.WriteLine("Current street: "
        + order.Address.AddressLine1);

    // Change the billing address.
    if (!order.Address.Equals(address))
    {
        // Use Address navigation property to change the association.
        order.Address = address;

        // Write the changed billing street address.
        Console.WriteLine("Changed street: "
            + order.Address.AddressLine1);
    }

    // If the address change succeeds, save the changes.
    context.SaveChanges();

    // Write the current billing street address.
    Console.WriteLine("Current street: "
        + order.Address.AddressLine1);
}

另請參閱

工作

HOW TO：使用外部索引鍵屬性變更物件間的關聯性
HOW TO：在關聯變更期間執行商務邏輯

概念

使用物件
定義及管理關聯性