CompareAttribute not working properly with bound properties on the Razor Page's PageModel

[RKDMax]

Is this a Bug or Feature request?:

Bug

Steps to reproduce (preferably a link to a GitHub repo with a repro project):

See This Repo to reproduce

Description of the problem:

When using a compare attribute on bound properties in the PageModel itself, the otherProperty parameter is not getting honoured and results in a "Could not find a property named <otherProperty>".

Version of Microsoft.AspNetCore.Mvc or Microsoft.AspNetCore.App or Microsoft.AspNetCore.All:

Microsoft.AspNetCore.App 2.1.0

[mkArtakMSFT]

Thanks for contacting us, @shanselman.
@dougbu, can you please look into this? Thanks!

[dougbu]

The difference between ThisDoesNotWorkModel and ThisWorksModel is the validation level at which the CompareAttribute is encountered. ValidationContext.ObjectType is typeof(string) instead of typeof(ThisDoesNotWorkModel) in your failing case because ModelValidationContext.Container is null for all top-level models i.e. controller or page model properties and action or handler parameters.

The workaround is exactly what you did in ThisWorksModel -- use [Compare] on a wrapper type instead of top-level models.

[dougbu]

@danroth27 @mkArtakMSFT @rynowak the new support for validation of top-level nodes does not pass the containing page model to ValidationAttributes, breaking [Compare] on page model properties. In addition, page model implementations of IValidatableObject are ignored. This is not what users should expect.

Though MVC passes an incorrectly-initialized ValidationContext for the page model property case, it's difficult to call this a bug since a fix enables new scenarios. Suggest we treat this as an enhancement for a near-term release. One possibility would be to validate the page model itself, passing a custom IValidationStrategy to ignore properties that were not bound. (Could also add a ValidationVisitor.Validate(...) overload accepting the container object and use it for page model property validation. That would address @RKDMax's scenario but not get page model IValidatableObject implementations working.)

[dougbu]

Cleared investigate label and my assignment. Over to you Triage team