Don't create a result on validation failure with MVC-Controllers and just continue the request pipeline

[snpz]

Hi.

I'm currently trying to implement AutoValidation for my controller methods. Validation happens as expected, but in case of a validation error the Controller-Action is never called as the pipeline gets aborted before.

I'd like to keep our current logic which looks something like this:

public ActionResult Update(PaymentInformationViewModel model)
{
    if (!ModelState.IsValid)
        return View("PaymentInformation/Update", model);

I think this could be handled by another configuration setting that defines to still continue running the pipeline even if a validation error occurs. Maybe I'm also overlooking some other possibility to reach my goal.

Any thoughts on this?

[snpz]

I just realized there is even an
open PR from @icnocop for something similar. Will this make it into the project?

[mvdgun]

Hi @snpz, I think it would be a nice feature to have and will make it into the project. I'm a little short on time at the moment so haven't gotten around to reviewing.

[unusualnan]

I’m also looking forward to this feature being merged.

[JimBobSquarePants]

I'm glad I found this discussion.

Given the link from the FluentValidations docs I was under the impression that this was a like-for-like replacement for the existing depreciated functionality. As it stands this is not the case and represents a significant breaking change.

[mvdgun]

@JimBobSquarePants I initially created this library to cater to my own needs being primarily automatic model validation for Web API projects. Over the time the project has grown and is adopting more features such as this one (when I get around to reviewing/merging :)).

[mvdgun]

I am working on a v2 release of the library. A part of the v2 release is going to be a result factory rework. It is going to be possible to return a null value to the action filter to prevent the action filter from short circuiting. Besides returning null I will also expose a new parameter that will allow you to prevent the validation filter from short circuiting the request.

public Task<IActionResult?> Create(MvcAutoValidationContext mvcAutoValidationContext)
{
    return Task.FromResult<IActionResult?>(null);
}

[JimBobSquarePants]

I'm feeling kinda dumb but how do you wire this up? I've got version 2

[snpz]

Have a look at the CustomResultFactory in README @JimBobSquarePants.

[JimBobSquarePants]

I'm sorry, I read the README and I still do not understand. I just want to be able to return the page with validation errors instead of some JSON result. I can see the override and have registered the example there, but the result is still the same.

This additional setup for what used to be out-of-the box behavior is quite a barrier.

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Index(Application application)
{
    // I WANT TO BE ABLE TO HIT THIS CODE AND RETURN MY PAGE WIH VALIDATION ERRORS.
    if (!this.ModelState.IsValid)
    {
        return this.View(application);
    }

    Index.Command command = new()
    {
        Application = application
    };

    _ = await this.mediator.Send(command);
    return this.RedirectToAction(nameof(this.ThankYou));
}

UPDATE.

GOT IT!!

In Program.cs

_ = builder.Services.AddValidatorsFromAssemblyContaining<ApplicationValidator>();
_ = builder.Services.AddFluentValidationAutoValidation(c =>
{
    // Disable the built-in .NET model (data annotations) validation.
    c.DisableBuiltInModelValidation = true;

    // Replace the default result factory with a custom implementation.
    c.OverrideDefaultResultFactoryWith<NullResultFactory>();
});

/// <summary>
/// A custom implementation of the <see cref="IFluentValidationAutoValidationResultFactory"/> interface that allows us to
/// control how validation results are converted into action results.
/// </summary>
/// <remarks>
/// Returning <see langword="null"/> prevents the auto-validation system from short-circuiting the action.
/// Validation errors are still added to <see cref="ActionExecutingContext"/> model state before this method is called,
/// so the controller action can inspect <c>ModelState.IsValid</c> and decide how to respond.
/// </remarks>
public class NullResultFactory : IFluentValidationAutoValidationResultFactory
{
    /// <inheritdoc/>
    public Task<IActionResult?> CreateActionResult(
        ActionExecutingContext context,
        ValidationProblemDetails validationProblemDetails,
        IDictionary<IValidationContext, ValidationResult> validationResults)
        => Task.FromResult<IActionResult?>(null);
}

[mvdgun]

@snpz I just released v2

[snpz]

Thanks for the release and mention, I will test this soon (in about 1-2 weeks probably) and give feedback if any.

[snpz]

I successfully transitioned from FluentValidation.AspNetCore to FluentValidation.AutoValidation without issues.

A few things that are specific to my use case took a bit longer, maybe it helps someone else:

• FluentValidation.AspNetCore also contained client-side validators we were using and I needed to reimplement that (I wasn't aware of that before)
• we were updating the ModelState after it has been validated (set entries to valid under some circumstances) and as FluentValidation.AutoValidation is implemented as an ActionFilter the order of execution wasn't correct anymore (I just moved the existing code for that to another ActionFilter and added it directly afterwards - problem gone)

Thanks again for putting that feature in.