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。 此示例还演示如何确保通过在上下文中调用 Dispose 以释放连接。
本主题中的示例基于 AdventureWorks 销售模型。 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实体框架。 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 = 43680
' Create a long-running context.
Dim context As New AdventureWorksEntities()
Try
If context.Connection.State <> ConnectionState.Open Then
' Explicitly open the connection.
context.Connection.Open()
End If
' Execute a query to return an order.
Dim order As SalesOrderHeader = context.SalesOrderHeaders.Where("it.SalesOrderID = @orderId", _
New ObjectParameter("orderId", orderId)).Execute(MergeOption.AppendOnly).First()
' Change the status of an existing order.
order.Status = 1
' You do not have to call the Load method to load the details for the order,
' because lazy loading is set to true
' by the constructor of the AdventureWorksEntities object.
' With lazy loading set to true the related objects are loaded when
' you access the navigation property. In this case SalesOrderDetails.
' Delete the first item in the order.
context.DeleteObject(order.SalesOrderDetails.First())
' Save changes.
If 0 < context.SaveChanges() Then
Console.WriteLine("Changes saved.")
End If
' Create a new SalesOrderDetail object.
' You can use the static CreateObjectName method (the Entity Framework
' adds this method to the generated entity types) instead of the new operator:
' SalesOrderDetail.CreateSalesOrderDetail(1, 0, 2, 750, 1, (decimal)2171.2942, 0, 0,
' Guid.NewGuid(), DateTime.Today));
Dim detail = New SalesOrderDetail With
{
.SalesOrderID = 0,
.SalesOrderDetailID = 0,
.OrderQty = 2,
.ProductID = 750,
.SpecialOfferID = 1,
.UnitPrice = CDec(2171.2942),
.UnitPriceDiscount = 0,
.LineTotal = 0,
.rowguid = Guid.NewGuid(),
.ModifiedDate = DateTime.Now
}
order.SalesOrderDetails.Add(detail)
' Save changes again.
If 0 < context.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.
context.Dispose()
// Define the order ID for the order we want.
int orderId = 43680;
// Create a long-running context.
AdventureWorksEntities context =
new AdventureWorksEntities();
try
{
if (context.Connection.State != ConnectionState.Open)
{
// Explicitly open the connection.
context.Connection.Open();
}
// Execute a query to return an order.
SalesOrderHeader order =
context.SalesOrderHeaders.Where(
"it.SalesOrderID = @orderId", new ObjectParameter("orderId", orderId))
.Execute(MergeOption.AppendOnly).First();
// Change the status of an existing order.
order.Status = 1;
// You do not have to call the Load method to load the details for the order,
// because lazy loading is set to true
// by the constructor of the AdventureWorksEntities object.
// With lazy loading set to true the related objects are loaded when
// you access the navigation property. In this case SalesOrderDetails.
// Delete the first item in the order.
context.DeleteObject(order.SalesOrderDetails.First());
// Save changes.
if (0 < context.SaveChanges())
{
Console.WriteLine("Changes saved.");
}
// Create a new SalesOrderDetail object.
// You can use the static CreateObjectName method (the Entity Framework
// adds this method to the generated entity types) instead of the new operator:
// SalesOrderDetail.CreateSalesOrderDetail(1, 0, 2, 750, 1, (decimal)2171.2942, 0, 0,
// Guid.NewGuid(), DateTime.Today));
SalesOrderDetail detail = new SalesOrderDetail
{
SalesOrderID = 0,
SalesOrderDetailID = 0,
OrderQty = 2,
ProductID = 750,
SpecialOfferID = 1,
UnitPrice = (decimal)2171.2942,
UnitPriceDiscount = 0,
LineTotal = 0,
rowguid = Guid.NewGuid(),
ModifiedDate = DateTime.Now
};
order.SalesOrderDetails.Add(detail);
// Save changes again.
if (0 < context.SaveChanges())
{
Console.WriteLine("Changes saved.");
}
}
catch (InvalidOperationException ex)
{
Console.WriteLine(ex.ToString());
}
finally
{
// Explicitly dispose of the context,
// which closes the connection.
context.Dispose();
}