Validator for Generic Request not found

I have a Generic SearchQuery used with MediatR

public record SearchQuery<TEntity, TEntityDto, TSearchDto>
    (TSearchDto Search) : IRequest<Result<PagedResultSet<TEntityDto>>>
    where TEntity : class, new()
    where TEntityDto : class, new()
    where TSearchDto : PagedResultsRequestDTO, new();

I defined a Validator for it:

public class SearchQueryValidator<TEntity, TEntityDto, TSearchDto> 
    : AbstractValidator<SearchQuery<TEntity, TEntityDto, TSearchDto>>
    where TEntity : class, new()
    where TEntityDto : class, new()
    where TSearchDto : PagedResultsRequestDTO, new()
{
    public SearchQueryValidator()
    {
        RuleFor(x => x.Search.PageSize).GreaterThan(0).
            WithMessage("Page size must be >= 0");
    }
}

There is a PipelineBehavior that handles the validation:

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

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

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

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

        var errorsDictionary = _validators
            .Select(x => x.Validate(context))
            .SelectMany(x => x.Errors)
            .Where(x => x != null);

        if (errorsDictionary.Any())
        {
            throw new ValidationException(errorsDictionary);
        }

        return await next();
    }
}

The validator and pipeline are registered

public static IServiceCollection AddApplication(this IServiceCollection services, IConfiguration configuration) =>
      services
          .AddAutoMapper(typeof(ApplicationServices))
          .AddMediatR(typeof(ApplicationServices).Assembly)
          .AddScoped<EventDispatcher>()
          .AddScoped(typeof(QueryService<,,>))
          .AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehavior<,>))
          .AddValidatorsFromAssemblyContaining(typeof(SearchQueryValidator<,,>),ServiceLifetime.Transient);

  public class ApplicationServicesModule : Module
  {
      protected override void Load(ContainerBuilder builder)
      {
          builder.RegisterGeneric(typeof(GetByIdHandler<,>)).AsImplementedInterfaces();
          builder.RegisterGeneric(typeof(GetLookupService<>)).AsImplementedInterfaces();
          builder.RegisterGeneric(typeof(SearchQueryHandler<,,>)).AsImplementedInterfaces();
      }
  }

However, if I set a breakpoint here, there are 0 Validators found, and it’s looking for the concrete SearchQuery signature:

What am I missing?

[jbogard]

Yep, MediatR delegates completely to the container to resolve services:

var behaviors = serviceProvider.GetServices<IPipelineBehavior<TRequest, TResponse>>();

No magic, pure DI. Try doing that yourself after registering everything, and if AutoFac can’t locate the services, it’s a registration or resolution problem.

[jbogard]

Yes typically open generics you have to register yourself (same with the MediatR.DI package). It’s too hard for these libraries to guess that you want to register open generics, they’ll only register the closed generics.