如何:使用导航运算符导航关系 (EntityClient)
本主题演示如何使用 EntityCommand 对象针对概念模型执行命令,以及如何使用 EntityDataReader 检索 RefType 结果。
运行本示例中的代码
将 AdventureWorks 销售模型添加到您的项目并将项目配置为使用实体框架 。 有关更多信息,请参见如何:使用实体数据模型向导(实体框架)。
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.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;
示例
以下示例显示如何通过使用 NAVIGATE (Entity SQL) 运算符导航 Entity SQL 中的关系。 Navigate 运算符具有以下参数:实体的实例、关系类型、关系的结束和关系的开始。 或者,您可以只将实体的实例和关系类型传递给 Navigate 运算符。
Using conn As New EntityConnection("name=AdventureWorksEntities")
conn.Open()
' Create an EntityCommand.
Using cmd As EntityCommand = conn.CreateCommand()
' Create an Entity SQL query.
Dim esqlQuery As String = "SELECT address.AddressID, (SELECT VALUE DEREF(soh) FROM " & _
" NAVIGATE(address, AdventureWorksModel.FK_SalesOrderHeader_Address_BillToAddressID) " & _
" AS soh) FROM AdventureWorksEntities.Addresses AS address"
cmd.CommandText = esqlQuery
' Execute the command.
Using rdr As DbDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)
' Start reading.
While rdr.Read()
Console.WriteLine(rdr("AddressID"))
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 an Entity SQL query.
string esqlQuery =
@"SELECT address.AddressID, (SELECT VALUE DEREF(soh) FROM
NAVIGATE(address, AdventureWorksModel.FK_SalesOrderHeader_Address_BillToAddressID)
AS soh) FROM AdventureWorksEntities.Addresses AS address";
cmd.CommandText = esqlQuery;
// Execute the command.
using (DbDataReader rdr = cmd.ExecuteReader(CommandBehavior.SequentialAccess))
{
// Start reading.
while (rdr.Read())
{
Console.WriteLine(rdr["AddressID"]);
}
}
}
conn.Close();
}