如果实体对象为null，则自动从操作方法中抛出404异常 [英] Automatically throw 404 exception from action method if entity object is null

问题描述

例如，我们有简单的操作方法来显示任何具有正确ID的书:

For example, we have simple action method to show any book with proper id:

public ActionResult GetBook(int id) // id = 123456789
    {
        var book = dataManager.Books.GetBookById(id); // == null
        logger.Info("Getting book with id " + book.Id);
        return View(book);
    }

如果 id 参数无效，则会出现500错误，因为没有书籍带有该ID.

If id parameter is not valid we get 500 error because there is no book with that id.

如果我们需要抛出404错误，我们必须手动处理这种情况，如下所示:

We have to handle this situation manually if we need to throw 404 error, like this:

if (book == null)
        {
            return HttpNotFound();
        }

是否有可能将Web应用程序中某处的所有操作方法(自定义过滤器，请求管道)的500错误切换为404错误?

Is it possible to switch 500-error to 404-error for all action methods somewhere in web-application (custom filter, request pipeline)?

推荐答案

从技术上讲，您可以通过安装错误处理程序，将500个内部服务器错误重写为在 Application_Error()中找不到的404，如下所示: ASP.NET MVC 5错误处理中进行了解释.

Technically you could, by installing an error handler, rewrite any 500 Internal Server Error to a 404 Not Found in Application_Error() as explained in ASP.NET MVC 5 error handling.

但是，您似乎想让代码在 book.Id 中的空 book 上引发 NullReferenceException ，并转为该异常进入404.

However, you seem to want to let your code throw a NullReferenceException on a null book in book.Id, and turn that exception into a 404.

在这种情况下，您真的不应该这样做，因为这会隐藏编程错误，因为您会错过无意间发生的异常.

You really shouldn't be doing that in this case, because this will hide programming errors, because you will miss the exceptions where this happened unintentionally.

所以:只需在您期望 null 的地方明确执行此操作即可.您显示的代码正是您所需要的:

So: just do this explicitly where you do expect a null. The code you showed is exactly what you need:

if (book == null)
{
    return HttpNotFound();
}

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