本主题提供一个示例，演示如何通过使用 EntityCommand 对实体数据模型执行命令，以及如何使用 EntityDataReader 检索嵌套集合结果。
运行本示例中的代码
将 AdventureWorks 销售模型添加到项目并将项目配置为使用实体框架。为此，请执行下列操作之一：
如果已安装实体数据模型工具，请完成如何：使用实体数据模型向导（实体框架） 中的过程。
否则，请完成如何：手动配置实体框架项目和如何：手动定义实体数据模型（实体框架） 中的过程。
在应用程序的代码页中，添加以下 using 语句（在 Visual Basic 中为 Imports）：
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.AdventureWorksModelusing 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;
示例
嵌套集合是指位于另一个集合内的集合。以下代码检索 Contacts 集合以及与每个 Contact 关联的 SalesOrderHeaders 的嵌套集合。
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();
}