ASP.NET MVC 3 RC 2 Routing problem - asp.net

Question

I changed the default routing in ASP.NET MVC from
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
);
to
routes.MapRoute(
"Default",
"{controller}/{action}/{id}/{lineNo}",
new { controller = "Home", action = "Index", id = UrlParameter.Optional, lineNo = UrlParameter.Optional });
but now all #Html.ActionLink() calls are rendered to href="". If I change the route back to default all links are working again.
I used the same route with RC1 and it worked perfectly.
I didn't find anything in the release docs so I think I'm doing it wrong.
Regards,
Steffen

Answer 1

In a route an optional parameter can appear only at the end. This means that in your route definition the id parameter cannot be optional. You need to explicitly set it to a value.
routes.MapRoute(
"Default",
"{controller}/{action}/{id}/{lineNo}",
new {
controller = "Home",
action = "Index",
lineNo = UrlParameter.Optional
}
);
And when you generate a link you must always provide a value for the id parameter if you want this route to match:
#Html.ActionLink("some link", "index", new { id = "123" })
As an alternative you might give a default value to the id parameter:
routes.MapRoute(
"Default",
"{controller}/{action}/{id}/{lineNo}",
new {
controller = "Home",
action = "Index",
id = "123",
lineNo = UrlParameter.Optional
}
);
Now you no longer need to specify it in your links.