c# - 定义 Context 对象的更好方法

Question

我想每次都使用实体框架上下文对象。在 asp.net 中定义的更好方法是什么？

前任：

using(employeeEntities context = new employeeEntities ())
    {

    }

我想在任何地方都使用这个上下文而不重用using

Answer 1

虽然您可以这样做，但微软建议以不同的方式使用上下文，请查看文档：

...
The lifetime of the ObjectContext begins when the instance is created and ends when the instance is either disposed or garbage-collected. Use using if you want all the resources that the context controls to be disposed at the end of the block. When you use using, the compiler creates a try/finally block and calls dispose in the finally block. Here are some general guidelines when deciding on the lifetime of the object context:

1. When working with long-running object context consider the following:
 - As you load more objects and their references into memory, the object
   context may grow quickly in memory consumption. This may cause

   performance issues.
 - Remember to dispose of the context when it is no longer required.
 - If an exception caused the object context to be in an unrecoverable
   state, the whole application may terminate.
 - The chances of running into concurrency-related issues increase as
   the gap between the time when the data is queried and updated grows.

2. When working with Web applications, **use an object context instance per request**... 

3. When working with Windows Presentation Foundation (WPF) or Windows Forms, use an object context instance per form. This lets you use change tracking functionality that object context provides. 
...

另外看看这个相关的线程：一个 DbContext per web request...为什么？

Answer 2

如果你只是想要一些语法糖来避免使用using但仍然每次都创建一个新的上下文，你可以编写一些扩展方法来帮助你编写如下代码：

// Execute is the extension method which takes the code 
// in the using block as a delegate
SomeEntities.Execute(context => 
    context.SomeTable.Where(item => item.Ammount > 100));

如果这是你想要的，我可以分享你的代码。如果您想一直使用单个上下文，请参阅 CloudyMarble 的答案。