Composite State Machine Events

A composite event is configured by specifying one or more events that must be consumed, after which the composite event will be raised. A composite event uses an instance property to keep track of the required events, which is specified during configuration.

To define a composite event, the required events must first be configured along with any event behaviors, after which the composite event can be configured.

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

    public int ReadyEventStatus { get; set; }
}

public class OrderStateMachine :
    MassTransitStateMachine<OrderState>
{
    public OrderStateMachine()
    {
        Initially(
            When(SubmitOrder)
                .TransitionTo(Submitted),
            When(OrderAccepted)
                .TransitionTo(Accepted));

        During(Submitted,
            When(OrderAccepted)
                .TransitionTo(Accepted));

        CompositeEvent(() => OrderReady, x => x.ReadyEventStatus, SubmitOrder, OrderAccepted);

        DuringAny(
            When(OrderReady)
                .Then(context => Console.WriteLine("Order Ready: {0}", context.Saga.CorrelationId)));
    }

    public Event OrderReady { get; private set; }
}

Once the SubmitOrder and OrderAccepted events have been consumed, the OrderReady event will be triggered.

Caution

The order of events being declared can impact the order in which they execute. Therefore, it is best to declare composite events at the end of the state machine declaration, after all other events and behaviors are declared. That way, the composite events will be raised after the dependent event behaviors.