HOW TO：變更 POCO 實體之間的關聯性 (Entity Framework)

在停用 Proxy 物件的建立或建立 POCO 實體但不包括它的 Proxy 物件時，您必須在 ObjectContext 上呼叫 DetectChanges 方法，才能將變更與 ObjectStateManager 同步化。 除了偵測純量屬性中的變更，這個方法會偵測關聯性中的變更，包括加入、刪除或變更相關物件。 如需詳細資訊，請參閱追蹤 POCO 實體中的變更 (Entity Framework)。 SaveChanges 方法會呼叫 DetectChanges，所以如果您不需要立即同步化關聯性，就不一定要明確呼叫 DetectChanges。

本主題中的範例會使用 HOW TO：定義 POCO 實體 (Entity Framework) 中所定義之 POCO 自訂資料類別，以及 HOW TO：自訂模型與對應檔以搭配自訂物件運作 (Entity Framework) 中所定義之 AdventureWorks 架構資料模型。

範例

此範例會將訂單目前的連絡人變更為不同的連絡人。 在將變更儲存至資料來源之前，SaveChanges 方法會呼叫 DetectChanges 方法。

Using context As New POCOAdventureWorksEntities()
    ' Disable proxy object creation. 
    context.ContextOptions.ProxyCreationEnabled = False
    Try
        ' Define the order and new address IDs. 
        Dim orderId As Integer = 43659
        Dim differentContactID As Integer = 5

        Dim order As Order = context.Orders.Include("Contact").Where(Function(o) o.SalesOrderID = orderId).First()

        ' Get contact to change to. 
        Dim differentContact As Contact = context.Contacts.First(Function(c) c.ContactID = differentContactID)

        ' The current contact. 
        Console.WriteLine("Original Contact Name: {0}", order.Contact.FirstName)

        ' The Entity Framework takes care of setting the other end of the relationship 
        ' when you call DetectChanges or SaveChanges (which calls DetectChanges). 
        ' However, there are scenarios when you are not working with ObjectContext 
        ' and will want to fix both ends of the relationship yourself 
        ' (for example, when working with disconnected objects). 

        ' Change the current ContactID to the new ContactID. 
        order.ContactID = differentContact.ContactID

        ' Because the change tracking is not enabled 
        ' The state manager will not be updated untill DetectChanges is called. 
        ' If context.ContextOptions.ProxyCreationEnabled was set to true (which is the default) 
        ' The changes would be synchronized righ away. 
        Console.WriteLine("The contact was updated, but DetectChanges was not yet called. ")
        Console.WriteLine("Contact Name: {0}", order.Contact.FirstName)
        context.DetectChanges()
        Console.WriteLine("After DetectChanges was called. Contact Name: {0}", order.Contact.FirstName)

        ' Call save the changes, which calls DetectChanges. 
        context.SaveChanges()
    Catch ex As UpdateException
        Console.WriteLine(ex.ToString())
    Catch ex As InvalidOperationException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (POCOAdventureWorksEntities context =
        new POCOAdventureWorksEntities())
{
    // Disable proxy object creation.
    context.ContextOptions.ProxyCreationEnabled = false;
    try
    {
        // Define the order and new address IDs.
        int orderId = 43659;
        int differentContactID = 5;

        Order order =
               context.Orders.Include("Contact")
               .Where(o => o.SalesOrderID == orderId).First();

        // Get contact to change to.
        Contact differentContact = context.Contacts.
            First(c => c.ContactID == differentContactID);
        
        // The current contact.
        Console.WriteLine("Original Contact Name: {0}", order.Contact.FirstName);

        // The Entity Framework takes care of setting the other end of the relationship
        // when you call DetectChanges or SaveChanges (which calls DetectChanges).
        // However, there are scenarios when you are not working with ObjectContext
        // and will want to fix both ends of the relationship yourself
        // (for example, when working with disconnected objects). 

        // Change the current ContactID to the new ContactID.
        order.ContactID = differentContact.ContactID;

        // Because the change tracking is not enabled
        // The state manager will not be updated untill DetectChanges is called.
        // If context.ContextOptions.ProxyCreationEnabled was set to true (which is the default)
        // The changes would be synchronized righ away. 
        Console.WriteLine("The contact was updated, but DetectChanges was not yet called. ");
        Console.WriteLine("Contact Name: {0}", order.Contact.FirstName);
        context.DetectChanges();
        Console.WriteLine("After DetectChanges was called. Contact Name: {0}",
            order.Contact.FirstName);

        // Call save the changes, which calls DetectChanges.
        context.SaveChanges();
    }
    catch (UpdateException ex)
    {
        Console.WriteLine(ex.ToString());
    }
    catch (InvalidOperationException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

另請參閱

概念

使用 POCO 實體 (Entity Framework)