HOW TO：執行可傳回巢狀集合的查詢 (EntityClient)

顯示如何使用 EntityCommand 物件針對概念模型執行命令，以及如何使用 EntityDataReader 擷取巢狀集合結果。

若要執行這個範例中的程式碼

1. 將 AdventureWorks 銷售模型 加入至專案中，並將專案設定為使用 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)。

2. 在應用程式的字碼頁中加入下列 using 陳述式 (在 Visual Basic 中為 Imports)：

   Imports System
   Imports System.Collections.Generic
   Imports System.Collections
   Imports System.Data.Common
   Imports System.Data
   Imports System.IO
   Imports System.Data.SqlClient
   Imports System.Data.EntityClient
   Imports System.Data.Metadata.Edm
   

   using System;
   using System.Collections.Generic;
   using System.Collections;
   using System.Data.Common;
   using System.Data;
   using System.IO;
   using System.Data.SqlClient;
   using System.Data.EntityClient;
   using System.Data.Metadata.Edm;
   

範例

「巢狀集合」(Nested Collection) 是位於另一個集合內的集合。 下列程式碼會擷取 Contacts 的集合，以及與每一個 Contact 相關聯的 SalesOrderHeaders 巢狀集合。

Using conn As New EntityConnection("name=AdventureWorksEntities")
    conn.Open()
    ' Create an EntityCommand. 
    Using cmd As EntityCommand = conn.CreateCommand()
        ' Create a nested query. 
        Dim esqlQuery As String = "Select c.ContactID, c.SalesOrderHeaders" & _
            " From AdventureWorksEntities.Contacts as c"

        cmd.CommandText = esqlQuery
        ' Execute the command. 
        Using rdr As EntityDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)
            ' The result returned by this query contains 
            ' ContactID and a nested collection of SalesOrderHeader items. 
            ' associated with this Contact. 
            While rdr.Read()
                ' the first column contains Contact ID. 
                Console.WriteLine("Contact ID: {0}", rdr("ContactID"))

                ' The second column contains a collection of SalesOrderHeader 
                ' items associated with the Contact. 
                Dim nestedReader As DbDataReader = rdr.GetDataReader(1)
                While nestedReader.Read()
                    Console.WriteLine(" SalesOrderID: {0} ", nestedReader("SalesOrderID"))
                    Console.WriteLine(" OrderDate: {0} ", nestedReader("OrderDate"))
                End While
            End While
        End Using
    End Using
    conn.Close()
End Using

using (EntityConnection conn =
    new EntityConnection("name=AdventureWorksEntities"))
{
    conn.Open();
    // Create an EntityCommand.
    using (EntityCommand cmd = conn.CreateCommand())
    {
        // Create a nested query.
        string esqlQuery =
            @"Select c.ContactID, c.SalesOrderHeaders
        From AdventureWorksEntities.Contacts as c";

        cmd.CommandText = esqlQuery;
        // Execute the command.
        using (EntityDataReader rdr =
            cmd.ExecuteReader(CommandBehavior.SequentialAccess))
        {
            // The result returned by this query contains 
            // ContactID and a nested collection of SalesOrderHeader items.
            // associated with this Contact.
            while (rdr.Read())
            {
                // the first column contains Contact ID.
                Console.WriteLine("Contact ID: {0}", rdr["ContactID"]);

                // The second column contains a collection of SalesOrderHeader 
                // items associated with the Contact.
                DbDataReader nestedReader = rdr.GetDataReader(1);
                while (nestedReader.Read())
                {
                    Console.WriteLine("   SalesOrderID: {0} ", nestedReader["SalesOrderID"]);
                    Console.WriteLine("   OrderDate: {0} ", nestedReader["OrderDate"]);
                }
            }
        }
    }
    conn.Close();
}

另請參閱

概念

Entity Framework 的 EntityClient 提供者