Async PropertyValidator Documentation

System Details

• FluentValidation version: 8.4.0 (via FluentValidation.AspNetCore 8.4.0)
• Web Framework version: ASP.NET Core 2.2

Issue Description

We’re currently investigating performance/deadlock issues in our codebase and a use of .GetAwaiter().GetResult() inside an implementation of a PropertyValidator’s IsValid method in an extremely hot path is concerning me.

I’ve looked at #999, but wanted to confirm that the suggestion to use AsyncValidatorBase will prevent our deadlocking issues. Specifically, that this line is OK: https://github.com/JeremySkinner/FluentValidation/blob/c24d6929f013b4ba003f0c6819c87672b0e984cf/src/FluentValidation/Validators/AsyncValidatorBase.cs#L49

If it’s all g, would be happy to help write up a docs PR on the use of this base class; just let me know.

Cheers, Ben

[JeremySkinner]

essentially I could/should just throw in the IsValid sync method to highlight any bad executions

Yes, that’s correct. I’m actually considering making this the default behavior for 9.0.

Is that applicable to ASP.NET Core as well

Yes. The model binding and validation processes in all versions of ASP.NET Core is synchronous.

If so, not sure how we’re going to work around that

You’d have to stop using automatic validation and instead inject the validators into your controllers. If your controller actions are then async, you can then directly invoke the validator’s ValidateAsync inside the controller action.

Keep in mind that the validation pipeline inside ASP.NET MVC / ASP.NET Core is basically designed entirely with the design of DataAnnotations attributes in mind, which don’t have any kind of concept of async execution. While FluentValidation does its best to plug into the pipeline, it’ll never be 100% perfect as FluentValidation and DataAnnotations are very different, so there will always be limitations like this.

Executing the validators directly will always give you the most control and allow you to fully utilize FluentValidation’s features, while MVC auto validation is more convenient, but also much more limited.

[benmccallum]

Thanks Jeremy. Kind of puzzling the asp.net core team didn’t go async in the validator pipeline. I’ll do some reading to find out why and if it’s on the horizon.

I think since we are using MediatR, I might introduce a middleware into the pipeline before our handlers that does the validation and uses ValidateAsync. I’m sure I won’t be the first to do this so will take a

Edit: Thanks for the further detail re: data annotations being an Achilles heel. Makes sense 😃