How to: Execute a Query that Returns Nested Collections (EntityClient)

This topic provides an example of how to execute a command against an Entity Data Model by using EntityCommand, and retrieve the nested collection results by using EntityDataReader.

To run the code in this example

1. Add the AdventureWorks Sales Model to your project and configure your project to use the Entity Framework. To do this, do one of the following:

   • If you have the Entity Dada Model tools installed, complete the procedure in How to: Use the Entity Data Model Wizard (Entity Framework).

   • Otherwise, complete the procedures in How to: Manually Configure an Entity Framework Project and How to: Manually Define an Entity Data Model (Entity Framework).

2. In the code page for your application, add the following using statements (Imports in Visual Basic):.

   Imports System
   Imports System.Collections.Generic
   Imports System.Collections
   Imports System.Data.Common
   Imports System.Data
   Imports System.Data.SqlClient
   Imports System.Data.EntityClient
   Imports System.Data.Metadata.Edm
   Imports System.IO
   ' Add AdventureWorksModel prepended with the root namespace for the project.
   'Imports ProjectName.AdventureWorksModel
   

   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 AdventureWorksModel;
   using System.Data.Metadata.Edm;
   

Example

A nested collection is a collection inside another collection. The following code retrieves a collection of Contacts and nested collections of SalesOrderHeaders associated with each Contact.

Using conn As EntityConnection = New EntityConnection("name=AdventureWorksEntities")
    conn.Open()
    Try
        ' Create an EntityCommand.
        Using cmd As EntityCommand = conn.CreateCommand()

            ' Create a nested query.
            Dim esqlQuery As String = "Select c.ContactID, c.SalesOrderHeader " & _
                    "From AdventureWorksEntities.Contact 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.
                Do While rdr.Read
                    ' the first column contains Contact ID.
                    Console.WriteLine("Contact ID: {0}", rdr.Item("ContactID"))

                    ' The second column contains a collection of SalesOrderHeader 
                    ' items associated with the Contact.
                    Dim nestedReader As DbDataReader = rdr.GetDataReader(1)
                    Do While nestedReader.Read
                        Console.WriteLine("   SalesOrderID: {0} ", nestedReader.Item("SalesOrderID"))
                        Console.WriteLine("   OrderDate: {0} ", nestedReader.Item("OrderDate"))
                    Loop
                Loop
            End Using
        End Using
    Catch ex As EntityException
        Console.WriteLine(ex.ToString())
    End Try

    conn.Close()
End Using

using (EntityConnection conn =
    new EntityConnection("name=AdventureWorksEntities"))
{
    conn.Open();
    try
    {
        // Create an EntityCommand.
        using (EntityCommand cmd = conn.CreateCommand())
        {
            // Create a nested query.
            string esqlQuery =
                @"Select c.ContactID, c.SalesOrderHeader
            From AdventureWorksEntities.Contact 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"]);
                    }
                }
            }
        }
    }
    catch (EntityException ex)
    {
        Console.WriteLine(ex.ToString());
    }
    conn.Close();
}

See Also

Other Resources

Working with EntityClient (Entity Framework Tasks)