如何:将 EntityConnection 用于对象上下文(实体框架)
本主题提供有关如何提供现有 EntityConnection 以供对象上下文使用的示例。有关更多信息,请参见管理对象上下文(实体框架)。
本主题中的示例基于 AdventureWorks 销售模型 (EDM)。若要运行本示例中的代码,必须已将 AdventureWorks 销售模型添加到您的项目中,并将项目配置为使用 Entity Framework。为此,请完成如何:使用实体数据模型向导(实体框架) 中的过程。
示例
本示例创建一个 EntityConnection,它将被传递到长时间运行的 ObjectContext 的构造函数中。此连接以手动方式建立。EntityConnection 和 ObjectContext 均以手动方式释放。
' Define the order ID for the order we want.
Dim orderId As Integer = 43661
' Create an EntityConnection.
Dim conn As New EntityConnection("name=AdventureWorksEntities")
' Create a long-running context with the connection.
Dim advWorksContext As New AdventureWorksEntities(conn)
Try
' Explicitly open the connection.
If Not conn.State = ConnectionState.Open Then
conn.Open()
End If
' Execute a query to return an order.
Dim order As SalesOrderHeader = _
advWorksContext.SalesOrderHeader.Where( _
"it.SalesOrderID = @orderId", New ObjectParameter("orderId", orderId)) _
.Execute(MergeOption.AppendOnly).First()
' Change the status of the order.
order.Status = 1
' Save changes.
If 0 < advWorksContext.SaveChanges() Then
Console.WriteLine("Changes saved.")
End If
' Load the order's items.
order.SalesOrderDetail.Load()
' Delete the first item.
advWorksContext _
.DeleteObject(order.SalesOrderDetail.First())
' Save changes again.
If 0 < advWorksContext.SaveChanges() Then
Console.WriteLine("Changes saved.")
End If
Catch ex As InvalidOperationException
Console.WriteLine(ex.ToString())
Finally
' Explicitly dispose of the context and the connection.
advWorksContext.Dispose()
conn.Dispose()
End Try
// Define the order ID for the order we want.
int orderId = 43661;
// Create an EntityConnection.
EntityConnection conn =
new EntityConnection("name=AdventureWorksEntities");
// Create a long-running context with the connection.
AdventureWorksEntities advWorksContext =
new AdventureWorksEntities(conn);
try
{
// Explicitly open the connection.
if (conn.State != ConnectionState.Open)
{
conn.Open();
}
// Execute a query to return an order.
SalesOrderHeader order =
advWorksContext.SalesOrderHeader.Where(
"it.SalesOrderID = @orderId", new ObjectParameter("orderId", orderId))
.Execute(MergeOption.AppendOnly).First();
// Change the status of the order.
order.Status = 1;
// Save changes.
if (0 < advWorksContext.SaveChanges())
{
Console.WriteLine("Changes saved.");
}
// Load the order's items.
order.SalesOrderDetail.Load();
// Delete the first item.
advWorksContext
.DeleteObject(order.SalesOrderDetail.First());
// Save changes again.
if (0 < advWorksContext.SaveChanges())
{
Console.WriteLine("Changes saved.");
}
}
catch (InvalidOperationException ex)
{
Console.WriteLine(ex.ToString());
}
finally
{
// Explicitly dispose of the context and the connection.
advWorksContext.Dispose();
conn.Dispose();
}