Allow adding failures programmatically

[ramduq]

FluentValidationValidator does not allow adding failures to the failure collection. This is needed in the following scenario:

Scenario
Client is a Blazor web assembly app. Server is an API project. Both perform validations using fluent validation. Thus, an API request from the client might get a response containing a List<ValidationFailure>. If it were possible to add these (backend) failures to the current collection, the UI would be updated accordingly (e.g. coloring the related fields in red).

Proposed solution

A new method

AddFailures(Dictionary<FieldIdentifier, List<ValidationFailure> failures)

** Alternatives considered**
I considered extending the class FluentValidationValidator in my project. However LastValidationResult (the dictionary of failures) is an internal field, which prevents accessing it from external projects.

An alternative solution would be to make this field protected, making it possible to manipulate this collection in derived classes.

[it4factory]

Upvote :)
Im actually trying to find out how to do exactly the same thing - display validation errors received from the server on WASM client form.

[Albiniivari]

You can add it to the EditContext messagestore, but you have to create a FieldIdentifier from the backend. It's a bit hacky when you get to an error in a collection. Cause then the backend would return something like "Key: Model.People[2].Name" which doesn't directly work as a fieldidentifier. If it's a simple property (not collection), you can do something like this

fieldIdentifier = new FieldIdentifier(myModel, err.Key); messageStore.Add(fieldIdentifier, err.Value);

[MarredCheese]

Cause then the backend would return something like something like "Key: Model.People[2].Name" which doesn't directly work as a fieldidentifier.

This repo already has the ability to translate paths to field identifiers:

FluentValidation/src/Blazored.FluentValidation/EditContextFluentValidationExtensions.cs

Line 181 in 8afbf82

private static FieldIdentifier ToFieldIdentifier(in EditContext editContext, in string propertyPath)

And it already uses that to copy the fluent validation results into the message store:

FluentValidation/src/Blazored.FluentValidation/EditContextFluentValidationExtensions.cs

Lines 52 to 55 in 8afbf82

	foreach (var validationResult in validationResults.Errors)
	{
	var fieldIdentifier = ToFieldIdentifier(editContext, validationResult.PropertyName);
	messages.Add(fieldIdentifier, validationResult.ErrorMessage);

So a method for manually adding backend errors could have a friendlier parameter type that doesn't involve FieldIdentifier. How about IDictionary<string, string[]> (mapping paths to error message lists)? It's the same type returned by ValidationResult.ToDictionary() and the same type as ValidationProblemDetails.Errors, which you'd likely have available in your server response.

[Albiniivari]

foreach (var validationResult in validationResults.Errors)
{
var fieldIdentifier = ToFieldIdentifier(editContext, validationResult.PropertyName);
messages.Add(fieldIdentifier, validationResult.ErrorMessage);

So a method for manually adding backend errors could have a friendlier parameter type that doesn't involve FieldIdentifier. How about IDictionary<string, string[]> (mapping paths to error message lists)? It's the same type returned by ValidationResult.ToDictionary() and the same type as ValidationProblemDetails.Errors, which you'd likely have available in your server response.

Yes that's exactly what I'd like. But when I try to add paths with collections to the errors, it doesn't correctly connect to the correct field. If I do it with a simple property such as "Name", then messages.Add(FieldIdentifier.Create(() => model.Name), validationResult.ErrorMessage); works correctly. But If it's a collection property such as "Addresses", so the path looks like "Model.Addresses[2].Street", then this doesn't work. (At least for me.)

Perhaps you have another way of doing this?

[slator]

Upvote :) Im actually trying to find out how to do exactly the same thing - display validation errors received from the server on WASM client form.

Same for me. What I ended up doing was using a bit of Reflection magic to access the CurrentEditContext contained in the FluentValidationValidator class. It gets the job done so far but must say I just wrote this piece of code and still testing for caveats and bugs.

Replace ErrorResponse with whatever fits to you needs.

public static class FluentValidationExtensions
{
    private static readonly PropertyInfo? CurrentEditContextProperty =
        typeof(FluentValidationValidator).GetProperty("CurrentEditContext", BindingFlags.NonPublic | BindingFlags.Instance);

    public static void AddServerErrors(this FluentValidationValidator validator, object model, ErrorResponse response)
    {
        ArgumentNullException.ThrowIfNull(validator);
        if (response.Errors is null) return;

        var editContext = CurrentEditContextProperty?.GetValue(validator) as EditContext;
        if (editContext is null)
        {
            throw new InvalidOperationException("Could not access CurrentEditContext from FluentValidationValidator");
        }

        var messageStore = new ValidationMessageStore(editContext);

        foreach (var kvp in response.Errors)
        {
            var fieldIdentifier = new FieldIdentifier(model, kvp.Key);
            foreach (var error in kvp.Value)
            {
                messageStore.Add(fieldIdentifier, error);
            }
        }

        editContext.OnFieldChanged += (s, e) => messageStore.Clear();
        editContext.NotifyValidationStateChanged();
    }
}