Question

Using APS.NET routing, how do you conditionally route to separate actions based on whether or not the request originated as an AJAX call?

For instance on a controller I may have two actions:

public ActionResult List() { return View(); }

and

public ActionResult ListJSON() { return Content(...); }

I’d like both actions to have the same URL, but ListJSON() should get called if the request originated as an AJAX call.

Answer 1

It turns out that you can easily define your own route constraints by implementing IRouteConstraint.

Something like this:

public class AjaxRouteConstraint : IRouteConstraint {
    public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection) {
        return httpContext.Request.IsAjaxRequest();
    }
}

Then simply use this constraint on a route. The trick is that the route with this constraint must come before the route without the constraint, otherwise the ajax route will never be called (the not-ajax route will always match).

There may be some consequences to doing this when it comes to URL generation. But I have not significantly tested those.