Blazor Custom Route Constraints

[GravlLift]

I am trying to use custom route constraint in Blazor, similar to how it currently works for both razor pages and MVC routes:

services.AddRouting(options =>
{
    options.ConstraintMap.Add("customName", typeof(MyCustomConstraint));
});

... but it appears that blazor route constraints do not consider any custom constraints that have been registered:

aspnetcore/src/Components/Components/src/Routing/RouteConstraint.cs

Lines 57 to 85 in af7c0cc

	private static RouteConstraint? CreateRouteConstraint(string constraint)
	{
	switch (constraint)
	{
	case "bool":
	return new TypeRouteConstraint<bool>(bool.TryParse);
	case "datetime":
	return new TypeRouteConstraint<DateTime>((string str, out DateTime result)
	=> DateTime.TryParse(str, CultureInfo.InvariantCulture, DateTimeStyles.None, out result));
	case "decimal":
	return new TypeRouteConstraint<decimal>((string str, out decimal result)
	=> decimal.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
	case "double":
	return new TypeRouteConstraint<double>((string str, out double result)
	=> double.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
	case "float":
	return new TypeRouteConstraint<float>((string str, out float result)
	=> float.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
	case "guid":
	return new TypeRouteConstraint<Guid>(Guid.TryParse);
	case "int":
	return new TypeRouteConstraint<int>((string str, out int result)
	=> int.TryParse(str, NumberStyles.Integer, CultureInfo.InvariantCulture, out result));
	case "long":
	return new TypeRouteConstraint<long>((string str, out long result)
	=> long.TryParse(str, NumberStyles.Integer, CultureInfo.InvariantCulture, out result));
	default:
	return null;
	}

So I instead encounter the ArgumentException, "Unsupported constraint '{constraint}' in route '{template}'.".

It would be ideal if RouteConstraint could be modified to reference RouteOptions.ContraintMap as the other routing engines do. Alternatively, needing to use some Blazor-specific registration method to register constraints only for Blazor would also be acceptable.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[javiercampos]

Extensible route constraints should be a must (and I thought that was already solved in asp.net ~12/13 years ago).
The SetParametersAsync parsing "hack" might work for some very contrived scenarios... but it completely disallows generalization, and even forbids doing certain scenarios without many more hacks...

Just imagine some route like: /users/{id}/{action:createOrEditConstraint} where you want one page to resolve both /create and /edit, but you want other different page to resolve /list (or others). Since you can't have user-defined constraints, /users/{id}/{action} matches both pages and you'll get an error.

Yes, it could be solved by creating -yet another component- and either redirect or include the create/edit component and list component in it, but that's yet another hack, and a ton more of boilerplate (one more component, with all its initialization and parsing per "CRUD" entity in a project).

One more scenario (which I used in razor pages/webapi/MVC a lot) is having short guids as parameters (while internally using Guid). Yes, you can just have a string and parse it on SetParametersAsync, but you can't generalize that (on a base class, for example), because you wouldn't have access to the inherited class parameter, so you basically need to specify the SetParameterAsync method and parse specifically on every single routable view with a short guid parameter (and again, since you can't constraint it -with a regex or something-, you can't distinguish it from other string routes).

Again, nothing that can't be "hacked away", but this is basic, and I'm sure many people (even those not on this thread) would miss this, so I believe affected-few doesn't look like a correct label here, to me.

[Tragen]

After 2 hours of debugging why my ulong constraint isn't working, I stumbled upon this bug.
For me it looks like a very basic feature. Please fix this soon.
Also ulong and uint should be added to the default constraints.