升级软件最难处理的问题之一是：您永远不会真正知道升级完成后应用程序是否还能够工作。

One of the trickiest parts about upgrading your software is that you never really know if your applications are going to work after the upgrade is complete.

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我们很快就会对使用案例进行编码，但是首先让我们来了解一下完成后的应用程序的页面将是什么样子。

We'll code the use cases soon, but first, let's take a look at what the pages will look like for the completed application.

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配置完成后，就可以编写应用程序逻辑了。

Now that configuration is complete, you can write some application logic.

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