MassTransit saga with Redis persistence gives Method Accpet does not have an implementation exception

0
votes

I'm trying to add Redis persistence to my saga which is managing calls to a routing slip (as well as additional messages to other consumers depending on the result of the routing slip) in the hopes that it will solve another timeout issue I keep getting.

However, I get an error message which goes in to my saga_error queue in RabbitMQ.

The error shown in the message is:

Method 'Accept' in type 'GreenPipes.DynamicInternal.Automatonymous.State' from assembly 'AutomatonymousGreenPipes.DynamicInternalc83411641fad46798326d78fe60522c9, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation

My correlation configuration code is:

InstanceState(s => s.CurrentState);

Event(() => RequestLinkEvent, x => x.CorrelateById(context => context.Message.LinkId).SelectId(y => y.Message.LinkId));
Event(() => LinkCreatedEvent, x => x.CorrelateById(context => context.Message.LinkId));
Event(() => CreateLinkGroupFailedEvent, x => x.CorrelateById(context => context.Message.LinkId));
Event(() => CreateLinkFailedEvent, x => x.CorrelateById(context => context.Message.LinkId));
Event(() => RequestLinkFailedEvent, x => x.CorrelateById(context => context.Message.LinkId));

Request(() => LinkRequest, x => x.UrlRequestId, cfg =>
            {
                cfg.ServiceAddress = new Uri($"{hostAddress}/{nameof(SelectUrlByPublicId)}");
                cfg.SchedulingServiceAddress = new Uri($"{hostAddress}/{nameof(SelectUrlByPublicId)}");
                cfg.Timeout = TimeSpan.FromSeconds(30);
            });

The LinkId in the above code is always a unique Guid.

The issue seems to happen when the saga is reading back an event that has been sent from my routing slip (be it a success or failure event).

An example event interface that is not working is:

public interface ILinkCreated
{
    Guid? CorrelationId { get; set; }
    int DatabaseId { get; set; }
    Guid LinkId { get; set; }
    string LinkName { get; set; }
}

If I switch back to an InMemorySagaRepository everything works (locally). I've tried so many different combinations of things and have now hit a brick wall.

I've updated all packages to the latest version. I've also been checking my redis database and can see that the state machine instance goes in each time correctly.

I also saw that someone on Google groups had the same issue but there's no response to their post.

2
asp.net-coreredismasstransitautomatonymous
Post your correlation configuration code. – Alexey Zimarev
I've updated my post – Ben Thomson
Post the code for your Event, my guess it is an interface with a method, and methods are not supported and should not be added to message contracts. Your Accept is probably that method. – Chris Patterson
I have updated my post. As you can see it's really simple interface and has no methods (the implementing class is identical too). I did originally think my interfaces might be causing it and have played around with a few different configurations but no luck. If you think it might be a bug in MT I might try and connect everything up and debug through it (I would love to be able to give help MT in some way as you guys have been super helpful and I love how it works). – Ben Thomson
I've been debugging through MassTransit.RedisIntegration and have found more out. The method Deserialize<T>(string json) in TypedDatabase.cs is where the error occurs. If you change T to my actual class (I copied it over to check) and then do Deserialize<MyClass> no errors occur. I think T comes through as a GreenPipes.DynamicInternal.Automatonymous.State type which I think is programmatically created in the GreenPipes DynamicImplementationBuilder.cs class. I'm guessing that adds the Accpet method but I don't understand enough of what's going on to fix it. – Ben Thomson

2 Answers

0
votes

The problem here is request-response.

It works like this:

  1. MT puts the request id to the saga state property UrlRequestId
  2. The request is sent
  3. You get a response back, the response contains the requestor address and the request id in its header
  4. MT uses saga repository to find your instance using repo.Find(x => x.UrlRequestId == message.Headers.RequestId) (hence this is not the real code but this is what happens)
  5. Redis (or any other KVS) doesn't support queries so we don't support queries in saga repositories too and you get "not implemented" exception

Your correlation specification for responses has no effect since Request always uses headers to find a saga instance for which the response belongs to.

You can workaround this by not using request-response and instead emit an event using context.Publish(new LinkCreatedEvent { ... , CorrelationId = context.Message.CorrelationId }) and using the usual correlation.

0
votes

So to answer my own question and perhaps shine a light on my own stupidity. The issue was in fact being caused by how I had setup my StateMachineInstance.

Instead of having CurrentState of type State as below:

public State CurrentState {get; set;}

I should have specified it as a string as such:

public string CurrentState { get; set;}

Now it can be deserialized in to the object correctly. I suspect this may have been causing my timeout issues with the InMemorySagaRepository on my staging server too.