Generating URL with page parameter fails with new endpoint routing (regression from 2.1)

[poke]

This appears to be a regression due to the new endpoint routing system in 2.2. As per aspnet/Mvc#7876, using parameter names action and page is somewhat difficult, however using a page parameter inside an MVC action or using an action parameter inside of a Razor page does work fine. At least it did.

With endpoint routing activated (through the MVC compatibility switch CompatibilityVersion.Version_2_2), generating an action link that has a page parameter will now fail iff Razor pages exist in the same project.

Steps to reproduce

Without Razor pages

1. Create new 2.2 application from standard MVC template.
2. Add an action to the HomeController:

   public IActionResult Test(int page)
   {
       return Json(new
       {
           Url = Url.Action(nameof(Test), new { page = 123 }),
           Page = page,
       });
   }

3. Launch the application and open http://localhost:5000/Home/Test?page=4
4. Observe the result which shows a generated URL /Home/Test?page=123.

Add Razor pages

5. Now, create a Razor page at Pages/Foo.cshtml with the contents @page.
6. Launch the application and open the previous URL again.
7. Observe that the generated URL is now null.

Disable endpoint routing

8. Disable endpoint routing by changing the AddMvc() call in Startup to set the compatibility level switch back to 2.1:

   services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

9. Launch the application and open the previous URL again.
10. Observe that the URL is generated properly again.

---

As you can see, endpoint routing breaks the URL generation here although the target URL exists just fine and although it also can be used properly the whole time (note that the JSON response always includes the passed page value). The mere presence of Razor pages should not make the URL generation treat any page parameter in a special way here.

[nickalbrecht]

I ran into this yesterday/today. Thanks for taking the time to flesh out the details and submit the bug @poke. My short term solution was to rename my action parameters to something like pageNum instead of page, But I'd prefer to see this get fixed so it wasn't so aggressive with regards to preventing the use of page as an action parameter when trying to generate URLs.

[WistfulWolf]

Just encountered this issue in .NET Core 2.1. UrlHelper.Link when adding a parameter with name "page" completely ignores it. Tested on clean MVC project with an API controller.

Api Controller class:

[ApiController, Route("api/[controller]")]
public class TestController : Controller
{
    [HttpGet(Name = "Test")]
    public void Test()
    {
    }
}

Page class:

public class AboutModel : PageModel
{
    public string Message { get; set; }

    public void OnGet()
    {
        string url = Url.Link("Test", new { page = 1 });
    }
}

The result is url = "http://localhost/api/Test"
Expected result is url = "http://localhost/api/Test?page=1"

[mkArtakMSFT]

Thanks for contacting us, @poke.
@JamesNK, can you please look into this? Thanks!

[mkArtakMSFT]

Ping @JamesNK!

[JamesNK]

I can reproduce this with endpoint routing. The issue comes from the new link generator requiring that page value be null because of the null page required value from MVC. A non-null value and the decision tree can't resolve the endpoint.

I tried a couple of minor changes to LinkGenerationDecisionTree, and I could get the link to successfully generate, but not without breaking at least some other routes. I'm not familiar with the inner workings of the link generator. @rynowak do you have some time to pair program this with me?

Test plus some broken attempts: b493845

[JamesNK]

Ryan and I looked into this issue. We don't think it is something that can be easily patched in 2.2. A fix will come in 3.0

If you have this problem then you should be able to fix it in 2.2 by disabling endpoint routing in Startup.cs where AddMvc is called:

services.AddMvc(options.EnableEndpointRouting = false)