HOW TO：使用查詢路徑來設定結果外觀 (Entity Framework)

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02/28/2011

本主題提供的範例將示範如何指定查詢路徑，以便定義在概念模型中查詢特定物件時所傳回的相關物件。這個範例中的查詢會傳回單一 Contact 物件，以及所有相關的 SalesOrderHeader 和 SalesOrderDetail 物件。

如果要指定查詢路徑，請將代表物件圖形的字串傳遞給 ObjectQuery 上的 Include 方法。 Include 方法可以套用在任何 Entity Framework 查詢的最上層：LINQ to Entities 、Entity SQL 或查詢產生器方法。

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

下列範例會指定查詢路徑，此路徑會傳回 Contact 及相關的 SalesOrderHeader 和 SalesOrderDetail 物件。

Using context As New AdventureWorksEntities()
    ' Define a LINQ query with a path that returns 
    ' orders and items for a contact. 
    Dim contacts = (From contact In context.Contacts.Include("SalesOrderHeaders.SalesOrderDetails") _
        Select contact).FirstOrDefault()

    ' Execute the query and display information for each item 
    ' in the orders that belong to the contact. 
    For Each order As SalesOrderHeader In contacts.SalesOrderHeaders
        Console.WriteLine(String.Format("PO Number: {0}", order.PurchaseOrderNumber))
        Console.WriteLine(String.Format("Order Date: {0}", order.OrderDate.ToString()))
        Console.WriteLine("Order items:")
        For Each item As SalesOrderDetail In order.SalesOrderDetails
            Console.WriteLine(String.Format("Product: {0} Quantity: {1}", _
                                              item.ProductID.ToString(), item.OrderQty.ToString()))
        Next
    Next
End Using

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    // Define a LINQ query with a path that returns 
    // orders and items for a contact.
    var contacts = (from contact in context.Contacts
                  .Include("SalesOrderHeaders.SalesOrderDetails")
                    select contact).FirstOrDefault();

    // Execute the query and display information for each item 
    // in the orders that belong to the contact.
    foreach (SalesOrderHeader order in contacts
        .SalesOrderHeaders)
    {
        Console.WriteLine(String.Format("PO Number: {0}",
            order.PurchaseOrderNumber));
        Console.WriteLine(String.Format("Order Date: {0}",
            order.OrderDate.ToString()));
        Console.WriteLine("Order items:");
        foreach (SalesOrderDetail item in order.SalesOrderDetails)
        {
            Console.WriteLine(String.Format("Product: {0} "
                + "Quantity: {1}", item.ProductID.ToString(),
                item.OrderQty.ToString()));
        }
    }
}

Include 方法會傳回查詢物件，而且您可以在 ObjectQuery 上多次呼叫這個方法，從多個關聯性納入實體，如下列範例所示。

' Create a SalesOrderHeader query with two query paths, 
' one that returns order items and a second that returns the 
' billing and shipping addresses for each order. 
Dim query As ObjectQuery(Of SalesOrderHeader) = context.SalesOrderHeaders.Include("SalesOrderDetails").Include("Address")

// Create a SalesOrderHeader query with two query paths, 
// one that returns order items and a second that returns the 
// billing and shipping addresses for each order.
ObjectQuery<SalesOrderHeader> query =
    context.SalesOrderHeaders.Include("SalesOrderDetails").Include("Address");

另請參閱

工作

HOW TO：執行傳回實體類型物件的查詢 (Entity Framework)
HOW TO：使用導覽屬性巡覽關聯性 (Entity Framework)

共用方式為

HOW TO：使用查詢路徑來設定結果外觀 (Entity Framework)

範例

另請參閱

工作

概念

其他資源