Asp.NET Web API throwing 404 instead of 400

Question

I have built a service in .NET 4.5 and Entity Framework 6, using the ASP.NET Web API template. When I make a GET request to the service and omit a required parameter, it is returning a 404 - Not Found, instead of a 400 - Bad Request. I tried checking to see if the required parameters are null, but it's not even reaching the code inside the method (see code below). My question is how do I change the default response or make it return 400 for missing required parameters.

[Route("item")]
[HttpGet]
public IHttpActionResult GetItem(string reqParam1, string reqParam2)
{
    if (reqParam1 == null || reqParam2 == null)
        throw new HttpResponseException(HttpStatusCode.BadRequest);

    //remainder of code here
}

Here is the webAPI.config file. I don't think that I have modified it from the default.

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

Just a note: the API isn't accessing information such as item/electronics/tvs but more like items where item is green and is square, where those descriptions are mandatory to pass in - so the query is like /item?color=green&shape=square.

Answer 1

The server returns a 404 because it cannot find the route you are trying to access. Actually the arguments should be a part of your route, as optionals or not: Route("items/{reqParam1}/{reqParam2}")

If you defined them as optionals the route should still be called if you use just items and you can throw the BadRequest. If not optionals then probably the NotFound will still be thrown.

You should also post the webApi config, so that we can see the base route mapping.

EDIT take the following route example:

config.Routes.MapHttpRoute(
            name: "RunsWithParams",
            routeTemplate: "api/{controller}/{project}/{skip}/{take}",
            defaults: new { take = RouteParameter.Optional, skip = RouteParameter.Optional }
        );

the project param is mandatory, the remaining are optional. you can call with just the project, or the remaining, and if you use just one of the Optionals then 404 is thrown, because the route is not defined. This is the same as using the decorators, so it does not exactly solve your issue, but explains a bit better the routing. Still, I don't see why you need a BadRequest in particular.

Yet another edit:

To use the request url parameters as you mention at the end of the post, you just need to use the [FromUri] decorator, see this page for more details, and a breef example follows:

// POST api/files/{project}?target={target}
public HttpResponseMessage Post(string project, string target, [FromUri]string fname){...}