Singleton NServiceBus Saga

Question

What would be the correct way to have all the messages processed by a single saga?

I don't think I can not specify some message-to-saga correlation. Can I? I believe it would result in a "saga not found" error.

A naive way would be to have some constant ID in the saga, but that seems wrong.

class SomePolicy :
    Saga<SomePolicy.State>,
    IAmStartedByMessages<SomeEvent>
{
    internal class State : ContainSagaData
    {
        public int Id { get { return 1; } }
    }

    protected override void ConfigureHowToFindSaga(SagaPropertyMapper<State> mapper)
    {
        mapper
            .ConfigureMapping<SomeEvent>(message => message.MagicConstant)
            .ToSaga(saga => saga.Id);
    }

    public void Handle(SomeEvent message)
    {
        // Modify the saga state here.
    }
}

This looks correct (didn't run the code), what is your issue? What are you trying to do? — Sean Farmar, Dec 22 '15 at 18:14
@TomRedfern let's say I want to aggregate some global information, such as how many times certain events occur in the system, I could use a singleton saga to receive all these events, increment some counter and perform an action when the counter reaches a certain threshold. — izildur, Dec 22 '15 at 23:53
@SeanFarmar I'm really just looking for some sort of best practice, if there is any. It feels wrong that I have to correlate things that way, given that correlation should always give the same result. — izildur, Dec 22 '15 at 23:56
But why do you need the correlation to give the same result? What's the functional reasoning behind this? What are you trying to accomplish? — Dennis van der Stelt, Dec 23 '15 at 08:00
If you can explain your business use case it will help to suggest a good solution, at the moment I find it difficult to understand what you are trying to achieve... There is no one solution for all scenarios, and your question sounds like a special case (to me) — Sean Farmar, Dec 23 '15 at 12:14

score 2 · Accepted Answer · answered Dec 23 '15 at 05:37

Rather than override ConfigureHowToFindSaga you can supply an implementation of IFindSagas<T>.Using<M> which is used to find a saga of type T from a message of type M. Then just have it always return the same instance.

See Complex Saga Finding Logic for more details and some samples.

Singleton NServiceBus Saga

1 Answers1