Validator Behavior

Validator Behavior in MediatR pipeline within RCommon.

The validator behavior is useful anytime you want to de-couple request/DTO validation from your application logic. This is implemented in in MediatR via a FluentValidation extension.

Implementation

The validator behavior is injected as part of the MediatR pipeline and performs validations on incoming requests which have objects that match the validation pattern that is registered automatically via dependency injection (see usage):

public class ValidatorBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : class, IAppRequest<TResponse>
{
    private readonly IValidationService _validationService;
    private readonly ILogger<ValidatorBehavior<TRequest, TResponse>> _logger;

    public ValidatorBehavior(IValidationService validationService, ILogger<ValidatorBehavior<TRequest, TResponse>> logger)
    {
        _validationService = validationService;
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
    {
        var typeName = request.GetGenericTypeName();

        _logger.LogInformation("----- Validating command {CommandType}", typeName);
        await _validationService.ValidateAsync<TRequest>(request, true, cancellationToken);
        return await next();
    }
}

Usage

Begin with dependency injection:

builder.Services.AddRCommon()
    .WithMediator<MediatRBuilder>(mediator =>
    {
        // Conventional dependency injection w/ MediatR
        mediator.Configure(config =>
        {
            config.RegisterServicesFromAssemblies((typeof(ApplicationServicesRegistration).GetTypeInfo().Assembly));
        });
        
        // Utilizing MediatR pipeline registrations
        mediator.AddValidationToRequestPipeline();
    });

Now create your validators using FluentValidation which is very well documented.