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 通常，您会将异常处理代码放在控制器中。 在您的术语中，我假设MVC控制器存在于您的“Web”层中，并且这些控制器调用“服务”层中的方法，例如您显示的“DeleteOrder”方法。 如果是这种情况，在DeleteOrder中的错误处理代码中，您应该抛出一个异常： 
 
if (order == null)
{
    throw new InvalidOperationException("Specified OrderId does not exist");
}
 
 这样，未处理的异常将传递给您的异常处理代码所在的控制器，在那里您可以记录异常并将用户重定向到相应的错误页面。 
 
 至于如何在控制器中处理异常，您有许多选择： 
 
 
 
 对每个操作方法使用try-catch块 
 
 
 通过实现OnException方法在控制器类上实现IExceptionFilter接口 
 
 
 使用内置的HandleErrorAttribute异常过滤器 
 
 
 创建自己的自定义异常处理过滤器 
 
 
 第四种方法（创建自己的异常过滤器）可能是最强大的方法。 在这里，您可以添加异常日志记录，以及根据引发的异常类型将用户重定向到适当的错误页面的代码。 
 
 您可以在此处找到MVC控制器异常处理的概述。 

Generally you would put your exception handling code in your controllers. In your terminology, I am assuming the the MVC controllers live in your "Web" layer, and that these controllers call methods in your "service" layer, such as the "DeleteOrder" method you've shown. If this is the case, in your error handling code in DeleteOrder, you should simply throw an exception:
 
if (order == null)
{
    throw new InvalidOperationException("Specified OrderId does not exist");
}
 
This way the unhandled exception will be passed to your controller, where your exception handling code lives, and there you can log the exception and redirect the user to the appropriate error page.
 
As far as how to handle the exception in your controller, you have a number of options:
 
 
 
Use a try-catch block for each action method
 
 
Implement the IExceptionFilter interface on your controller class by implementing the OnException method
 
 
Use the built-in HandleErrorAttribute exception filter
 
 
Create your own custom exception handling filter
 
 
The fourth method (create your own exception filter) is probably the most robust way to go. In here, you can add exception logging, as well as code to redirect the user to an appropriate error page based on the type of exception that is thrown.
 
You can find a good overview of MVC controller exception handling here.