Question regarding IPipelineBehavior

Hi, I’m trying to use the IPipelineBehavior in a very specific way and (probably - likely - very much) I’m missing something because it is not working.

All my requests are of type IRequest<OperationResult> or IRequest<OperationResult<TResult>>. OperationResult is a class that’s basically a way for me to return a (possible) failed result, with errors, and if the result is not failed, a way to attach a value to it (the generic version).

Now, I want to add in a pipeline so I can short-circuit the flow if some condition is met. I then defined my pipeline like this: public sealed class AuthorizationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, OperationResult<TResponse>> where TRequest : class, IRequest<OperationResult<TResponse>> but on execution that throws because TResponse is not the type I want (the result type), but the type of the IResult<T>.

Of course that I can’t define an AuthorizationBehavior<TRequest, OperationResult<TResponse>>. That’s not valid. So, I’m blind right now as I don’t know how to define the pipeline in order for me to be able to short-circuit it, without throwing an exception, and be able to return my own OperationResult<TResponse> inside the handler if I need to…

Any hints or ideas? Maybe I’m using this wrong and I have to do it in another way?

[jbogard]

Yes! I should blog about this more 😛

On Thu, Nov 16, 2017 at 11:29 AM, Ricardo Peres [e-mail] wrote:

Not exactly the same, but similar: I want to register an implementation of IPipelineBehavior for a concrete type, like: svcs.AddScoped<IPipelineBehavior<Command, Command>, CommandPipelineBehavior>();

however, the CommandPipelineBehavior class is never resolved! But if I register an open implementation:

svcs.AddScoped<IPipelineBehavior<, >, GenericPipelineBehavior<, >>();

it does! Is this supposed to? Thanks!

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[jhoiby]

Oops, figured it out finally!

For others to reference, here is how I setup my validation pipeline behavior to return result metadata:

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

        public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators, ILogger logger)
        {
            _validators = validators ?? throw new ArgumentNullException(nameof(validators));
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        }

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

            if (failures.Count != 0)
            {
                CommonResult validationResult = new CommonResult(
                    messageId: request.MessageId,
                    outcome: Outcome.MessageValidationFailure,
                    flashMessage: "A validation error occured in request " + typeof(TRequest),
                    errors: failures.ToCommonResultErrorCollection() );

                validationResult.LogErrors(typeof(TRequest), CorrelationId, _logger);

                return Task.FromResult(validationResult as TResponse);
            }

            return next();
        }
    }

Feedback is welcome!