Track using a saga

Because Routing Slips carry their state on the wire, it’s not possible to query the state of a currently executing routing slip. Use this pattern when your solution requires tracking the progress of a Routing Slip that’s in-flight.

Build a routing slip

var builder = new RoutingSlipBuilder(NewId.NextGuid());

// add your activities as normal
builder.AddActivity("DownloadImage", new Uri("queue:download-image_execute?bind=false"),
    new
    {
        ImageUri = new Uri("https://images.google.com/someImage.jpg")
    });
builder.AddActivity("FilterImage", new Uri("queue:filter-image_execute?bind=false"));
builder.AddVariable("WorkPath", @"\dfs\work");

Create the saga state machine

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

public class MonitorRoutingSlip :
    MassTransitStateMachine<MonitorState>
{
    public MonitorRoutingSlip()
    {
        InstanceState(x => x.CurrentState);

        Event(() => RoutingSlipCompleted, x => x.CorrelateById(context => context.Message.TrackingNumber));

        During(Initial, Active,
            When(RoutingSlipActivityCompleted)
                .Then(context => context.Saga.CurrentActivity = context.Message.ActivityName)
                .TransitionTo(Active),
            When(RoutingSlipCompleted)
                .Then(context => context.Saga.CurrentActivity = "Completed")
                .TransitionTo(Completed)
        );
    }

    public State Completed { get; private set; }
    public State Active { get; private set; }

    public Event<RoutingSlipActivityCompleted> RoutingSlipActivityCompleted { get; private set; }
    public Event<RoutingSlipCompleted> RoutingSlipCompleted { get; private set; }
}

Add a subscription to the routing slip

builder.AddSubscription(new Uri("queue:monitor-state?bind=false"),
    RoutingSlipEvents.Completed | RoutingSlipEvents.ActivityCompleted);

var routingSlip = builder.Build();