ValidatorPipeline.cs

public class MediatorPipeline<TRequest, TResponse> 
  : IRequestHandler<TRequest, TResponse>
  where TRequest : IRequest<TResponse>
{
    private readonly IRequestHandler<TRequest, TResponse> _inner;
    private readonly IEnumearble<IMessageValidator<TRequest>> _validators;

    public MediatorPipeline(IRequestHandler<TRequest, TResponse> inner,
        IEnumerable<IMessageValidator<TRequest>> validators)
    {
        _inner = inner;
        _validators = validators;
    }

    public TResponse Handle(TRequest message)
    {
        using (LogContext.PushProperty(LogConstants.MediatRRequestType, requestType))
        using (Metrics.Time(Timers.MediatRRequest))
        {
            var failuers = _validators
                .Select(v => v.Validate(message))
                .SelectMany(result => result.Errors)
                .Where(f => f != null)
                .ToList();
            if (failures.Any())
                throw new ValidationException(failures);
            
            return _inner.Handle(request);
        }
    }
 }