如何：在长时间运行的对象上下文中管理连接（实体框架）

本主题提供有关如何手动为长时间运行的对象上下文打开连接的示例。此示例还说明如何确保通过在上下文中调用 Dispose 以释放连接。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

本示例手动打开由长时间运行的 ObjectContext 使用的连接，然后执行查询并保存更改。当释放 ObjectContext 时，将关闭此连接。

' Define the order ID for the order we want.
Dim orderId As Integer = 43661

' Create a long-running context.
Dim advWorksContext As New AdventureWorksEntities()
Try
    ' Explicitly open the connection.
    If Not advWorksContext.Connection.State = ConnectionState.Open Then
        advWorksContext.Connection.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, 
    ' which closes the connection. 
    advWorksContext.Dispose()
End Try

// Define the order ID for the order we want.
int orderId = 43661;

// Create a long-running context.
AdventureWorksEntities advWorksContext =
    new AdventureWorksEntities();
try
{
    if (advWorksContext.Connection.State != ConnectionState.Open)
    {
        // Explicitly open the connection.
        advWorksContext.Connection.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, 
    // which closes the connection. 
    advWorksContext.Dispose();
}

另请参见

任务

如何：在长时间运行的对象上下文中管理连接（实体框架）
如何：手动从对象上下文打开连接（实体框架）