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HOW TO:在 EntityCollection 中查詢相關物件 (Entity Framework)

本主題提供的範例將示範如何在關聯性導覽屬性所傳回的 EntityCollection 中查詢相關物件。

本主題的範例是根據 Adventure Works Sales Model。若要執行此範例中的程式碼,您必須已經將 AdventureWorks Sales Model 加入到專案中,並設定您的專案使用 實體架構。若要這樣做,請完成 HOW TO:手動設定 Entity Framework 專案HOW TO:以手動方式定義 Entity Data Model (Entity Framework) 中的程序。您也可以使用 [Entity Data Model 精靈] 定義 AdventureWorks Sales Model。如需詳細資訊,請參閱 HOW TO:使用 Entity Data Model 精靈 (Entity Framework)

範例

這個範例會載入與特定連絡人有關之 SalesOrderHeader 物件的集合,然後使用 LINQ 運算式來傳回已經出貨之線上訂單的清單。

' Specify the customer ID.
Dim customerId As Integer = 4332

Using context As AdventureWorksEntities = _
    New AdventureWorksEntities()
    Try
        ' Get a specified customer by contact ID.
        Dim customer = (From customers In context.Contact _
            Where customers.ContactID = customerId _
            Select customers).First()

        ' Load the customer orders if not already loaded.
        If Not customer.SalesOrderHeader.IsLoaded Then
            customer.SalesOrderHeader.Load()
        End If

        ' Write the number of orders for the customer.
        Console.WriteLine("Customer '{0}' has placed {1} total orders.", _
            customer.LastName, customer.SalesOrderHeader.Count)

        ' Get the online orders that have shipped.
        Dim shippedOrders = _
        From order In customer.SalesOrderHeader _
            Where order.OnlineOrderFlag = True _
            And order.Status = 5 _
            Select order

        ' Write the number of orders placed online.
        Console.WriteLine("{0} orders placed online have been shipped.", _
            shippedOrders.Count())
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using
// Specify the customer ID.
int customerId = 4332;

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    try
    {
        // Get a specified customer by contact ID.
        var customer = (from customers in context.Contact
            where customers.ContactID == customerId 
            select customers).First();
        
        // Load the customer orders if not already loaded.
        if (!customer.SalesOrderHeader.IsLoaded)
        {
            customer.SalesOrderHeader.Load();
        }

        // Write the number of orders for the customer.
        Console.WriteLine("Customer '{0}' has placed {1} total orders.",
            customer.LastName, customer.SalesOrderHeader.Count);

        // Get the online orders that have shipped.
        var shippedOrders =
            from order in customer.SalesOrderHeader
            where order.OnlineOrderFlag == true
            && order.Status == 5
            select order;

        // Write the number of orders placed online.
        Console.WriteLine("{0} orders placed online have been shipped.",
            shippedOrders.Count());
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

此範例會針對 SalesOrderHeader 物件的集合使用相同的 LINQ 查詢來當做第一個範例。CreateSourceQuery 方法是用來只載入查詢所傳回的物件,而不會在一開始將所有相關的物件載入集合中。然後會在 SalesOrderHeader 關聯性導覽屬性所傳回的 EntityCollection 上呼叫 Load 方法。

' Specify the customer ID.
Dim customerId As Integer = 4332

Using context As AdventureWorksEntities = _
    New AdventureWorksEntities()
    Try
        ' Get a specified customer by contact ID.
        Dim customer = (From customers In context.Contact _
                        Where customers.ContactID = customerId _
                        Select customers).First()

        ' Use CreateSourceQuery to generate a query that returns 
        ' only the online orders that have shipped.
        Dim shippedOrders = _
        From orders In customer.SalesOrderHeader.CreateSourceQuery() _
            Where orders.OnlineOrderFlag = True _
            And orders.Status = 5 _
            Select orders

        ' Write the number of orders placed online.
        Console.WriteLine("{0} orders placed online have been shipped.", _
            shippedOrders.Count())

        ' Load the remaining orders for this customer.
        If Not customer.SalesOrderHeader.IsLoaded Then
            customer.SalesOrderHeader.Load()
        End If

        ' Write the number of total orders for the customer.
        Console.WriteLine("Customer '{0}' has placed {1} total orders.", _
            customer.LastName, customer.SalesOrderHeader.Count)

    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using
// Specify the customer ID.
int customerId = 4332;

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    try
    {
        // Get a specified customer by contact ID.
        var customer = (from customers in context.Contact
                        where customers.ContactID == customerId
                        select customers).First();

        // Use CreateSourceQuery to generate a query that returns 
        // only the online orders that have shipped.
        var shippedOrders =
            from orders in customer.SalesOrderHeader.CreateSourceQuery()
            where orders.OnlineOrderFlag == true
            && orders.Status == 5
            select orders;

        // Write the number of orders placed online.
        Console.WriteLine("{0} orders placed online have been shipped.",
            shippedOrders.Count());

        // Load the remaining orders for this customer.
        if (!customer.SalesOrderHeader.IsLoaded)
        {
            customer.SalesOrderHeader.Load();
        }

        // Write the number of total orders for the customer.
        Console.WriteLine("Customer '{0}' has placed {1} total orders.",
            customer.LastName, customer.SalesOrderHeader.Count);
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

另請參閱

工作

HOW TO:執行傳回實體類型的查詢 (Entity Framework)
HOW TO:使用查詢路徑來設定結果外觀 (Entity Framework)
HOW TO:使用導覽屬性巡覽關聯性 (Entity Framework)

概念

為查詢結果定形 (Entity Framework)