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 Entity Framework 。若要這樣做，請完成 HOW TO：手動設定 Entity Framework 專案和 HOW TO：手動定義模型和對應檔 (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：使用實體資料模型精靈 (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 New AdventureWorksEntities()
    ' Get a specified customer by contact ID. 
    Dim customer = (From customers In context.Contacts _
        Where customers.ContactID = customerId _
        Select customers).First()

    ' You do not have to call the Load method to load the orders for the customer, 
    ' 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 SalesOrderHeaders. 

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

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

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

// Specify the customer ID.
int customerId = 4332;

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

    // You do not have to call the Load method to load the orders for the customer,
    // 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 SalesOrderHeaders.

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

    // Get the online orders that have shipped.
    var shippedOrders =
        from order in customer.SalesOrderHeaders
        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());
}

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 New AdventureWorksEntities()
    ' Get a specified customer by contact ID. 
    Dim customer = (From customers In context.Contacts
        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.SalesOrderHeaders.CreateSourceQuery() _
        Where orders.OnlineOrderFlag = True AndAlso orders.Status = 5 _
        Select orders

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

    ' You do not have to call the Load method to load the orders for the customer, 
    ' 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 SalesOrderHeaders. 

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

// Specify the customer ID.
int customerId = 4332;

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    // Get a specified customer by contact ID.
    var customer = (from customers in context.Contacts
                    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.SalesOrderHeaders.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());

    // You do not have to call the Load method to load the orders for the customer,
    // 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 SalesOrderHeaders.

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

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

載入相關的物件 (Entity Framework)