Checking for nulls in ASP.NET MVC Controllers

Question

Another opinion question:

What is the proper (in your opinion) to check for nulls in an MVC controller. For instance, if you have an edit controller that fetches a record from the db based on an id, what do you do if that record is not found? I found this article, but I'm not sure I like that method. Do you just check for it with an if statement and redirect to a 404 page? What solution do you use?

Answer 1

That's what I do in my blog:

public ActionResult DisplayPublication (int nr)
{
    if (!PublicationExists (nr))
        throw new (HttpException (404, ""));

    // ....

    return ...;
}

As a general rule of a thumb, if a resource is requested which does not in fact exist, return HTTP 404. Definitely not return 200 OK along with the message about the missing resource. If not found, should be 404. If you changed the structure of your urls, consider 301 Moved Permanently.

Depending on the type and logic of the software you're developing, you may decide to exercise a different reaction to that situation, it's up to you.

Answer 2

I don't know if it's best practice, but I check with an if and redirect to a "NotFound" view that states "The company/client/whatever you requested does not exist or was deleted."

Did it this way simply b/c I followed the NerdDinner tutorial when setting up the skeleton of my site, and that's how they do it.

Answer 3

I use a method similar to the article you linked to: an action filter that returns a 404 if the view model is null. I've combined it with a custom action invoker (like this) so that I don't have to put the filter attribute on everything.

Since I mentioned it, there are several other types of actions you can do if you go the action filter route. I have/had filters that will:

1. Automatically redirect to the Index view after a successful edit.
2. Redirect to the same page if the ModelState is invalid.
3. Redirect to an access denied page if a security exception is thrown.

I'm thinking about refactoring these to a convention registry so I can have something like:

When.ModelIsNull.RedirectTo<SharedController>(c => c.NotFound());
For("Edit").ModelStateIsInvalid.Redisplay();
For("Edit").OnSuccess.RedirectTo("Index");
On<SecurityException>().RedirectTo<SharedController>(c => c.AccessDenied());

Then if I wanted to change how a particular behavior works I just change it in one place. For example, instead of going to Index, I could redirect to the View view.

For("Edit").OnSuccess.RedirectTo("View");

I hope this gives you some ideas.

Edit: Here is how to could accomplish something similar using FubuMVC (which I love to steal ideas from)