Using 'UseMvc' to configure MVC is not supported while using Endpoint Routing. To continue using 'UseMvc', please set 'MvcOptions.EnableEndpointRouting = false' inside 'ConfigureServices'. (Razor Pages)

[jomeno]

Scenario.

I just upgraded a .netcoreapp2.2 Razor Pages web app (also containing some controllers annotated as [ApiController]) to .netcoreapp3.3 using the docs at https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-2.2&tabs=visual-studio#update-routing-startup-code.

Afterwards, Javascript calls to the Api controllers started returning 404 until I included:
app.UseMvc() in Configure method in Startup.cs which led to this warning message:

"Using 'UseMvc' to configure MVC is not supported while using Endpoint Routing. To continue using 'UseMvc', please set 'MvcOptions.EnableEndpointRouting = false' inside 'ConfigureServices'"

Everything worked fine after adding services.AddMvc(o => o.EnableEndpointRouting = false) in ConfigureServices in Startup.cs.

Question

Shouldn't services.AddRazorPages() provide out-of-the-box working support for Api controllers or accept an option config to enable it without the need to UseMvc()?

What’s in AddRazorPages()

This updates in .NET Core 3.0 blog post by @danroth27 clearly mentions that AddRazorPages() excludes some API-focused feautures:
https://devblogs.microsoft.com/aspnet/asp-net-core-updates-in-net-core-3-0-preview-4/

[javiercn]

Shouldn't services.AddRazorPages() provide out-of-the-box working support for Api controllers or accept an option config to enable it without the need to UseMvc()?

No, AddRazorPages just adds support for using RazorPages and no controllers. You can call AddControllers and then call app.MapRazorPages() and app.MapControllers() as below

app.UseEndpoints(endpoints => 
{
    endpoints.MapRazorPages();
    endpoints.MapControllers();
});

[jomeno]

Oh perfect! Warning is gone now. Thanks!