ASP.NET MVC custom routes with optional args - asp.net-mvc

Question

I want a Route with two optional args; I thought the following would work:
routes.MapRoute(
"ProductForm",
"products/{action}/{vendor_id}_{category_id}",
new { controller = "Products", action = "Index", vendor_id = "", category_id = "" },
new { action = #"Create|Edit" }
);
But it only works when both vendor_id and category_id are provided; using RouteDebug I see that /products/create/_3 doesn't trigger my route, so I added other two routes:
routes.MapRoute(
"ProductForm1",
"{controller}/{action}/_{category_id}",
new { controller = "Home", action = "Index", category_id = "" },
new { controller = "Products", action = #"Create|Edit" }
);
routes.MapRoute(
"ProductForm2",
"{controller}/{action}/{vendor_id}_",
new { controller = "Home", action = "Index", vendor_id = "" },
new { controller = "Products", action = #"Create|Edit" }
);
So, the questions:
Is using three routes the only way to make a route with optional args?
Are these URLs ok or not, that is, would you suggest a better way to do this?

Answer 1

Why don't you try to give vendor_id a default value (if it is not specified i.e 0) that would help you get away with one route
routes.MapRoute("ProductForm","products/{action}/{vendor_id}_{category_id}",
new { controller = "Products", action = "Index", vendor_id = "0", category_id = "" },
new { action = #"Create|Edit" });

Answer 2

looks good to me but i would do it a little different:
routes.MapRoute(
"ProductForm1",
"product/category/{category_id}",
new { controller = "Home", action = "Index", category_id = "" },
new { controller = "Products", action = #"Create|Edit" }
);
and then
routes.MapRoute(
"ProductForm1",
"product/details/{product_id}",
new { controller = "Home", action = "Index", product_id = "" },
new { controller = "Products", action = #"Create|Edit" }
);
then your class can be as follows:
ActionResults Index(){}
ActionResults Index(int category_id){// get categories}
ActionResults Index(int product_id){ // get products}
but thats just me

Answer 3

you could try it like this:
routes.MapRoute(
"ProductForm",
"products/{action}/{arg1}/{arg1_id}/{arg2}/{arg2_id}",
new { controller = "Products", action = "Index", arg1 = "", arg2 = "", arg1_id = "", arg2_id = "" },
new { action = #"Create|Edit" });
Then you would create some logic in your actionresult method to check arg1 and arg2 and identify wich argument has been passed in.
your actionlink urls would look like this:
/products/create/vendor/10
/products/create/category/20
/products/create/vendor/10/category/20
/products/create/category/20/vendor/10
Personally i dont like this as the route doesn't seem very clean but should give you what i think your looking to achieve?