I have seen this question a couple of times here in SO but none of them with any acceptable answer:
ASP.NET MVC @Url.Action includes current route data
ASP.NET MVC implicitly adds route values
Basically I have Controller with an action method called Group, it has an overload that receives no parameters and displays a list of elements and another one that receives an id and displays details for that group.
If I do something like this:
Url.Action("Group", "Groups");
From the main page of the site (/) it returns an url like this:
"mysite.com/Groups/Group"
which is alright
Now, if the current address of the site is /Groups/Group/1
And I call the same method
Url.Action("Group", "Groups");
the returned url is this:
"mysite.com/Groups/Group/1"
It automatically adds the value of the route for the current page when generating the URL.
Even if I generate the URL this way:
Url.Action("Group", "Groups", null);
Thus explicitly specifying that I don't want any route values, the generated URL is the same.
To get the address I want I have to explicitly set the route value to an empty string, like so:
Url.Action("Group", "Groups", new {id=""});
This will generate the following url:
"mysite.com/Groups/Group"
My question is, why does this happen? If I don't set any route values it shouldn't add them to the generated URL.
Best Answer
Url.Action will reuse the current request parameters, if you do not explicitly set them. It is by design in outbound url-matching algorithm. When looking for the route data parameters in a process of generating url, parameters are taken from:
1) explicitly provided values
2) values from the current request
3) defaults
In the order I specified above.
Outbound matching algorithm for routes is complicated, so it is good practice to explicitly set all parameters for request, as you did in your example