How do we add a validation handler into the pipeline of the Meditr

[sokrethchhem]

How do we add a validator handle into the pipeline with Blazor-State?

[sokrethchhem]

This blazor-state librarie is great. I just need setup in the MediatR and I have my validation handle.

services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly());
services.AddBlazorState
(
    (aOptions) => aOptions.Assemblies =
        new Assembly[]
        {
            typeof(Program).GetTypeInfo().Assembly,
        }
);
services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehavior<,>));

[paulreicherdt]

Can you please share this example again? I'm trying to implement a validation behavior for actions. But without success :(

[sokrethchhem]

Paul you need to add, In Program.cs or Startup.cs

builder.Services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly());
builder.Services.AddBlazorState
(
    (options) =>
    {
        options.UseReduxDevTools();
        options.Assemblies =
        new Assembly[]
        {
            typeof(Program).GetTypeInfo().Assembly,
        };
    }
);
builder.Services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehavior<,>));

---

And ValidationBehavior.cs

public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
    {
        private readonly IEnumerable<IValidator<TRequest>> _validators;

        public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
        {
            _validators = validators;
        }

        public Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
        {
            var context = new ValidationContext<TRequest>(request);
            var failures = _validators
                .Select(v => v.Validate(context))
                .SelectMany(result => result.Errors)
                .Where(f => f != null)
                .ToList();

            if (failures.Count != 0)
            {
                throw new ValidationException(failures);
            }

            return next();
        }
    }

Then create CreateHandlerValidator.cs for the action

public class CreateHandlerValidator : AbstractValidator<CreateFaqAction>
        {
            public CreateHandlerValidator(FaqValidator faqValidator)
            {
                RuleFor(v => v.faq).SetValidator(faqValidator);
            }
        }

[paulreicherdt]

Hm this is actually exactly what I did...

Program.cs

builder.Services
    .AddBlazorState
    (
        options =>
        {
            options.UseReduxDevTools();
            options.Assemblies =
                new[]
                {
                    typeof(Program).GetTypeInfo().Assembly,
                };
        }
    )    
    .AddValidatorsFromAssembly(Assembly.GetExecutingAssembly())
    .AddTransient(typeof(IPipelineBehavior<,>), typeof(FluentValidationBehavior<,>));

FluentValidationBehavior.cs

internal class FluentValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    private readonly IEnumerable<IValidator<TRequest>> _validators;

    public FluentValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
    {
        _validators = validators;
    }

    public Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        if (!_validators.Any())
        {
            return next();
        }

        var context = new ValidationContext<TRequest>(request);

        var failures = _validators
            .Select(x => x.Validate(context))
            .SelectMany(result => result.Errors)
            .Where(f => f != null)
            .ToList();

        if (failures.Count == 0)
        {
            return next();
        }

        failures.Insert(0, new ValidationFailure($"{request.GetType().Name}", $"{failures.Count} validation error(s)."));

        throw new ValidationException(failures);
    }
}

IncrementCountAction and Validator

public partial class CounterState
{
    public class IncrementCountAction : IAction
    {
        public int Amount { get; init; }
    }
    
}

public class IncrementCountActionValidator : AbstractValidator<CounterState.IncrementCountAction>
{
    public IncrementCountActionValidator()
    {
        RuleFor(x => x.Amount).GreaterThan(0);
    }
}

But it doesn't work. The behavior and validator are not triggered. The action just go directly into the handler.
What do I wrong?

Thank you
Paul

[paulreicherdt]

@StevenTCramer any ideas?

[paulreicherdt]

Ok, got it to work. Since the changed within MediatR 12, the behavior needs to be changed
From:

internal class FluentValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
}

to

internal class FluentValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest
{
}

as the IAction does not have a Response.