Redirect to referrer URL but add something to the querystring

Question

Using ASP.Net MVC, I'm posting off to an action (where I'm then adding an email address to a DB table etc.)

I need to re-direct back to the referrer URL but also need to add something to the querystring of the referrer URL. This action can be called from many places, so I can't redirect to an action in the current controller.

How do I re-direct to the referrer and add something to the query string (bearing in mind that the referrer might already have query string values that I'll need to preserve).

[HttpPost]
public ActionResult MyAction(MyModel model)
{
    //Do stuff.

    return new RedirectResult(Request.UrlReferrer.ToString()); // + query string value?
}

Thanks!

Answer 1

Use an UriBuilder and HttpUtility.ParseQueryString:

[HttpPost]
public ActionResult MyAction(MyModel model)
{
    //Do stuff.

    UriBuilder uriBuilder = new UriBuilder(Request.UrlReferrer);
    NameValueCollection query = HttpUtility.ParseQueryString(uriBuilder.Query);
    query.Add("myparam", "something");
    uriBuilder.Query = query.ToString();

    return new RedirectResult(uriBuilder.Uri);
}