Determine the used route when multiple MVC routes are assigned to one action method.

Is your feature request related to a problem? Please describe.

I have the following code:

[Route("item/up/{id}")]
[Route("item/down/{id}")]
public IActionResult Move([FromRoute]string action, [FromRoute]int id)
{
}

Consider /item/up/155. The problem is that when I check the value of action, then it does not contain the value up, but the value Move.

It may be by design, but it seems odd to me as the controller name is not transformed into ItemController.

Describe the solution you'd like

I would like action to have the value of the actual route parameter, not the value of the action method.

Describe alternatives you've considered

I can parse Request.Path.Value (="/item/up/155"), but I'd prefer not to as I would like to keep things simple.

[rynowak]

You might be able to find what you need from ActionContext.RouteData.Route.

A very low tech solution would be to make this two separate action methods, and put the implementation in a third private method that they both call. If you want to handle both of these URLs, but slightly differently that would be my suggestion.

The solution you mention is what I originally had. I just tried to refactor the code.

When I look at ControllerContext.RouteData the value of action is Move. As expected because that's the value I see in the action parameter of the method.

RouteData.Values:

• id: 155
• action: Move
• controller: Item

But why does action have the value Move?

It makes no sense to me as Move is not a value in the route. And it seems not consistent compared to controller. Then I would've expected controller to be ItemController.

The question is, should this considered to be a bug?

I would prefer to have the routes registered so it doesn't reach the action method in case of a mismatch.

When I use [Route("[controller]/{direction}/{id}")] then this would catch everything inside the controller. Being an MVC controller other actions (like Create, Edit) become unreachable. I can solve this by either placing it in a seperate controller or moving it to a sub path: [Route("[controller]/move/{direction}/{id}")]

In that case direction has the value up. The downside is that I need to check direction for a valid value, as all requests now enter the action method. But since I need to do this anyway this may not be a problem.

[rynowak]

The question is, should this considered to be a bug?

This is how routing works in MVC. Actions and controllers are assigned names, those names are used for URL generation and view lookup.

In that case direction has the value up. The downside is that I need to check direction for a valid value, as all requests now enter the action method. But since I need to do this anyway this may not be a problem.

Implementing a route constraint might be what you want: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/routing?view=aspnetcore-2.1#route-constraint-reference

---

Can you start from the beginning and explain what it is that you're trying to accomplish? Code samples will help.

In my project I use default mvc routes. I have an mvc controller which contains something like this:

public IActionResult Create()
{
    return View();
}

[HttpPost]
public async Task<IActionResult> Create(ViewModel.Post post)
{
}

public IActionResult Up(int id)
{
    return Move(id, "up");
}

public IActionResult Down(int id)
{
    return Move(id, "down");
}

private IActionResult Move(int id, string action)
{
    // ...

    switch (action)
    {
        case "up":
        case "down":
    }

    // ...

    return LocalRedirect(link);
}

There is absolutely nothing wrong with the code. It works and is easy to maintain. But I thought that it could be refactored. Like documented I can add multiple routes to one method:

[Route("")]
[Route("Home")]
[Route("Home/Index")]
public IActionResult Index()
{
    return View();
}

I want to do something similar, but with one difference. I need to know which route was taken.
In order to register the Up and Down route I use Route attributes:

[Route("[controller]/up/{id}")]
[Route("[controller]/down/{id}")]
public IActionResult Move(string action, int id)
{
    // ...

    switch (action)
    {
        case "up":
        case "down":
    }

    // ...

    return LocalRedirect(link);
}

If I'm not mistaken then in both versions the same routes are registered. And actually this works, but there is one problem. There is no easy way to find out what the exact route was. When I look at RouteData.Values then action is Move instead of Up.

I understand that this is not a bug and that these values are meant for other purposes, but I am missing the equivalent of the taken route. Usually you won't need it as the routes have the same meaning: "" == "Home" == "Home/Index". But not in this case.

Solution 1) The only information I found was Request.Path, but I would need to parse it. I haven't found an easy way to do this, but it may be quite easy to create a PathString extension to parse the path which can be used like Request.Path.Values.

Solution 2) I've tried other options like [Route("[controller]/{direction}/{id}")]. The main difference here is that direction accepts all values, instead of only up and down. Since I do have to check the value in all cases this may not be an issue, but I would prefer not to enter the action method at all if the route is invalid.

Another problem is that all actions are routed to this method, so my Create method becomes unreachable. In that case I would need to split the controller or add a sub path: [Route("[controller]/move/{direction}/{id}")]

Solution 3) Use route constraints. To narrow the possible paths I can use a regular expression.

[Route("[controller]/{direction:regex(^(up|down)$)}/{id}")]
public IActionResult Move(string action, string direction, int id)

The value of action is Move and direction contains the value of the taken route. So this works. Thanks for suggesting route constrains, I didn't think of it.

BTW, in the documentation action was used as parameter name, but that doesn't seem to work: Error: The attribute route 'Item/{action:regex(^(up|down)$)}/{id}' cannot contain a parameter named '{action}'. Use '[action]' in the route template to insert the value 'Move'.

Solution 4) Leave it as it is.

Option 1 needs extra work, option 2 is not really an option considering all issues, so I have two options left: use regex as route constraint or leave it as it is. I think both options are equally easy, but with the regex I have less lines. I will go for option 3. Thanks again for suggesting route constraints.

Thank you for your comments. It really helped me.

[poke]

But why does action have the value Move`?

The route parameters action and controller are special parameters that are set by the MVC framework to determine the actual action method that is used to handle the request.

In your case, you get controller=Item and action=Move because the action that handles the incoming request is ItemController.Move.

If you want action to contain different values, then you have to split up the action into separate ones.

Note that multiple routes on a single action are not meant as a way to overload an action for the purpose of doing different things. You can parameterize an action using route parameters but in your case, having separate actions still appears to be the clearer solution.

As for why there isn't a route parameter set automatically to up or down, that's simply because the framework won't make random guesses here. The route could easily be /something/very/long/with/many/parts/that/could/be/parameters. How would the teamwork possibly decide what to use as parameters there (and what those would be called). The only choice is for you to specify what parts are variable parameters.

@poke

Note that multiple routes on a single action are not meant as a way to overload an action for the purpose of doing different things.

Do you have a source on that? Because that was my first thought, and why I would otherwise have chosen for split actions. But given the example {action:regex(^(list|get|create)$)} I don't think it it's a bad design by default.

Direction is the parameter and action is just not part of the path (like [Route("Home")]). It's equivalent to [Route("[controller]/[action]/{direction:regex(^(up|down)$)}/{id}")], except that action is now part of the path.

I think that it depends on the situation and in this case the chosen solution is fine. It's clear what happens and seperate actions have no added value.

[rynowak]

Solution 3) Use route constraints. To narrow the possible paths I can use a regular expression.

[Route("[controller]/{direction:regex(^(up|down)$)}/{id}")]
public IActionResult Move(string action, string direction, int id)

Having read through the background information you provided, this is what I'd recommend.

One thing I want to mention about this is that it means that a URL that provides an invalid value for a direction will result in a 404 rather than you action method being called so that you can decide how to respond.

The distinction here is whether you want to return a meaningful error message when invalid data is passed this way, or if you were prefer to not handle the request and have it 404.

[mkArtakMSFT]

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