Hooking into the new validation system

[Ducki]

The new validation system from MinimalAPIs support recursive validation of objects.
It was said in #28640 (comment) by @danroth27:

Our preference is that the object graph validation logic is a generic component that ships as part of the core .NET libraries instead of as an ASP.NET Core specific component. This logic could then be used for minimal APIs, Blazor, and anyone else that needs it.

Now with the RC, I can't seem to find an easy way to use the new system. Judging by some source code, the [ValidatableType] attribute only gets considered in the context of endpoints, but not when used on arbitrary objects.

So is there any way so make use of the new validation for custom objects within e.g. my own services?

[BrennanConroy]

Types are automatically gathered for validation by either being part of the Map* method (e.g. MapGet([Required] string s)) or by having the [ValidatableType] attribute on the type and the source generator running. Validation then runs as an EndpointFilter automatically by the framework.

When you say arbitrary objects, if it's in the context of ASP.NET Core, then use [ValidatableType]. If you're talking about a console app, or custom logic outside of a minimal endpoint, then you'd need to do a bit more work of registering IValidatableInfoResolver's and calling validation yourself. Here is an example where I was playing around with calling validation myself on Hub Methods: d803d95#diff-5ebd3ff07dfc4b8ce6a099034eb36fde60deb15a8f39a8ebe1cc45d5cb95b01dR709