How can I correlate events in a masstransit state machine without using a Guid?

Question

I have defined the following state machine in Masstransit:

public class OrderStateMachine : MassTransitStateMachine<OrderState>
{
    public OrderStateMachine()
    {
        InstanceState(x => x.Status);

        Event(() => OrderCreated, x => x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode).SelectId(ctx => NewId.NextGuid()));

        //How should I select an id for these events?
        Event(() => OrderProvisioned, x => x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode));
        Event(() => OrderInvoiced, x => x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode));

        State(() => Created);
        State(() => Finished);

        CompositeEvent(() => OrderFinished, order => order.CompositeStatus, OrderProvisioned, OrderInvoiced);

        Initially(
            When(OrderCreated)
                .Then(context => Console.WriteLine("Order created"))
                .TransitionTo(Created));

        During(Created,
            When(OrderFinished)
                .Then(context => Console.WriteLine("Order finished"))
                .TransitionTo(Finished)
                .Finalize());

    }

    public State Created { get; set; }
    public State Finished { get; set; }

    public Event<OrderCreated> OrderCreated { get; set; }
    public Event<OrderProvisioned> OrderProvisioned { get; set; }
    public Event<OrderInvoiced> OrderInvoiced { get; set; }
    public Event OrderFinished { get; set; }

}

public class OrderState : SagaStateMachineInstance
{
    public Guid CorrelationId { get; set; }

    public string OrderCode { get; set; }
    public string Status { get; set; }
    public CompositeEventStatus CompositeStatus { get; set; }

}

public class OrderCreated
{
    public string OrderCode { get; set; }

    public OrderCreated(string orderCode)
    {
        OrderCode = orderCode;
    }
}

public class OrderInvoiced
{
    public string OrderCode { get; set; }

    public OrderInvoiced(string orderCode)
    {
        OrderCode = orderCode;
    }

}

public class OrderProvisioned
{
    public string OrderCode { get; set; }

    public OrderProvisioned(string orderCode)
    {
        OrderCode = orderCode;
    }
}

How can I correlate the OrderProvisoned and the OrderInvoiced event to the same OrderState instance as the initial OrderCreated event without sending Guids in my events and only use the ordercode property to correlate them? If I run this example, I never get the OrderFinished event if both OrderProvisioned and OrderInvoiced are sent, but if I add Guids to the events and correlate them based on that Guid it is executed correctly.

Sven Schelfaut · Accepted Answer · 2016-02-11T08:39:31.433

I solved it, apparently you must explicitly set the custom correlationid on the statemachine instance, I would expect that masstransit would do that for me. So this is the adapted code for the initial state:

            Initially(
            When(OrderCreated)
                .Then(context => context.Instance.OrderCode = context.Data.OrderCode)
                .Then(context => Console.WriteLine("Order created"))
                .TransitionTo(Created));

Also using a saga factory works, but I would think that you could drop the selectid logic as the saga factory overrules this, but than I get an exception.

        Event(() => OrderCreated,
            x =>
            {
                x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode);
                x.InsertOnInitial = true;
                x.SetSagaFactory(context => new OrderState
                {
                    CorrelationId = NewId.NextGuid(),
                    OrderCode = context.Message.OrderCode
                });
                x.SelectId(context => NewId.NextGuid());
            });

FYI, the `x.SelectId(...)` call is superfluous as the `SetSagaFactory` is creating the saga and initializing the value. I should verify, but I believe this is correct. — Chris Patterson, Jan 17 '17 at 15:14
I tried leaving out `SelectId`, but then I get a "The correlationId was not present and the saga could not be created" error. What does work is when I leave `SelectId` in to generate a new GUID, and then in the saga factory lambda I use `context.CorrelationId` to assign to the state's CorrelationId. This to avoid creating two GUIDs where the first one would just be thrown out. — Sipke Schoorstra, Oct 18 '19 at 12:52

score 1 · Answer 2 · answered Feb 05 '16 at 18:18

Is there a broken unit test that would be usable to see if this behavior is not working? From the edited code above, that seems to be how I would expect it to be correlated - using the OrderCode. That's how the shopping cart example works as well.

The SelectId() function is only needed for an event that initiates the state machine, since that is where the CorrelationId is assigned. If it isn't used by the other events, there is no need to "select" it since the Query (the orderCode) would do the correlation.

That's how the shopping cart example works in the sample: https://github.com/MassTransit/Sample-ShoppingWeb/blob/master/src/CartTracking/ShoppingCartStateMachine.cs#L15

In your example above:

Event(() => OrderCreated, x => x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode).SelectId(ctx => NewId.NextGuid()));

Event(() => OrderProvisioned, x => x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode));
Event(() => OrderInvoiced, x => x.CorrelateBy(order => order.OrderCode, ctx => ctx.Message.OrderCode));

This is exactly how I would configure it, and it seems like you're on the right track.

I solved it, apparently you must explicitly set the custom correlationid on the statemachine instance, I would expect that masstransit would do that for me. — Sven Schelfaut, Feb 11 '16 at 08:09

How can I correlate events in a masstransit state machine without using a Guid?

2 Answers2