Question

My MVC2 app uses a component that makes subsequent AJAX calls back to the same action, which causes all kinds of unnecessary data access and processing on the server. The component vendor suggests I re-route those subsequent requests to a different action. The subsequent requests differ in that they have a particular query string, and I want to know whether I can put constraints on the query string in my route table.

For example, the initial request comes in with a URL like http://localhost/document/display/1. This can be handled by the default route. I want to write a custom route to handle URLs like http://localhost/document/display/1?vendorParam1=blah1&script=blah.js and http://localhost/document/display/1?vendorParam2=blah2&script=blah.js by detecting “vendor” in the URL.

I tried the following, but it throws a System.ArgumentException: The route URL cannot start with a '/' or '~' character and it cannot contain a '?' character.:

routes.MapRoute(
   null,
   "Document/Display/{id}?{args}",
   new { controller = "OtherController", action = "OtherAction" },
   new RouteValueDictionary { { "args", "vendor" } });

Can I write a route that takes the query string into account? If not, do you have any other ideas?

---

Update: Put simply, can I write routing constraints such that http://localhost/document/display/1 is routed to the DocumentController.Display action but http://localhost/document/display/1?vendorParam1=blah1&script=blah.js is routed to the VendorController.Display action? Eventually, I would like any URL whose query string contains “vendor” to be routed to the VendorController.Display action.

I understand the first URL can be handled by the default route, but what about the second? Is it possible to do this at all? After lots of trial and error on my part, it looks like the answer is “No”.

Answer 1

QueryString parameters can be used in constraints, although it’s not supported by default. Here you can find an article describing how to implement this in ASP.NET MVC 2.

As it is in Dutch, here’s the implementation. Add an ‘IRouteConstraint’ class:

public class QueryStringConstraint : IRouteConstraint 
{ 
    private readonly Regex _regex; 

    public QueryStringConstraint(string regex) 
    { 
        _regex = new Regex(regex, RegexOptions.IgnoreCase); 
    } 

    public bool Match (HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection) 
    { 
        // check whether the paramname is in the QS collection
        if(httpContext.Request.QueryString.AllKeys.Contains(parameterName)) 
        { 
            // validate on the given regex
            return _regex.Match(httpContext.Request.QueryString[parameterName]).Success; 
        } 
        // or return false
        return false; 
    } 
}

Now you can use this in your routes:

routes.MapRoute("object-contact", 
    "{aanbod}", 
    /* ... */, 
    new { pagina = new QueryStringConstraint("some|constraint") });