ASP.NET MVC: Attributes and Semi Dynamic Check for Request Parameters

If I were self involved I would say something silly like IN THIS AWESOME POST but I’m not. However in this post that is awesome I gave some examples of how to use attributes to set defaults or just check to see if an incoming id could be matched to a record somewhere… Sorry lost my track of thought. Watching the begining of Transformers… You know the part where it could have been good.

Anyway, I figured I’d add another debatable use for an attribute, the CheckForGivenRequest one. Basically in the other post I had something that was specific it was checking for, this is used if you are checking for a request parameter but you don’t want to make an attribute for each and every one of them.

  //This is so you can use it many times on the same method
  //I know, I know... duh
  [AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
  public sealed class CheckForGivenRequestAttribute : ActionFilterAttribute
    //The constructor to set what should be looked for
    //Default amount is what it should be set if not there
    public CheckForGivenRequestAttribute(String requestParameterName, Object defaultAmount)
      DefaultAmount = defaultAmount;
      RequestParameterName = requestParameterName;

    public override void OnActionExecuting(ActionExecutingContext filterContext)
      //Check the extra request parameters (ie &someId=1) for if it exists
      //If it doesn't exist, then add it
      if (!filterContext.ActionParameters.ContainsKey(RequestParameterName))
        filterContext.ActionParameters.Add(RequestParameterName, null);

      //If it's null set to the default
      filterContext.ActionParameters[RequestParameterName] =
         filterContext.ActionParameters[RequestParameterName] ?? DefaultAmount;

    //Just the properties, nothing to see here.  Go away...
    private Object DefaultAmount { get; set; }
    private String RequestParameterName { get; set; }

And then the use of it:

  [CheckForGivenRequestAttribute("someStupidId", 1)]
  public ActionResult INeedAnExample(Int32 someStupidId)

Now you might ask why not make that attiribute generic to avoid boxing.

Why not make that attribute generic to avoid boxing?

Glad you asked. Turns out that you can’t make attributes generic. Aparrently it’s somwhat debatable why but not possible at the time being. Besides, the ActionParameters collection is <String, Object> anyhow, so at some point any stuct would be boxed anyhow.

On a side note, I never noticed this before, but when one of the non descript Autobots crashes near a pool, some kid is there to ask if he is the Tooth Fairy? Seriously? Are kids really that dumb? Cause every picture I’ve seen of the Tooth Fairy has been a 20 foot tall metal thing with no discernible features.