MassTransit Saga State to Instance State Mapping

Question

I'm new to MassTransit, and I can't seem to figure out how it maps the States that I define on a saga (MassTransitStateMachine) to the "State" property on the related SagaStateMachineInstance class.

For example, if I have a state machine class with three states:

public class MySaga :
   MassTransitStateMachine<MySagaState>
{
    public State Executing { get; private set; }
    public State Completed { get; private set; }
    public State Failed { get; private set; }
    ...
}

And my state machine instance class has a "State" property

public class MySagaState : SagaStateMachineInstance
{
    public Guid CorrelationId { get; set; }
    public int State { get; set; }
}

How does MT decide which saga state is which integer?

There also appear to be two built-in saga states, "Initial" and "Final", so this example would have 5 states. How is the State to integer mapping done?

score 5 · Answer 1 · answered Apr 07 '17 at 16:25

You need to specify the states in order to assign numbers to them as part of the state machine definition:

public class MySaga :
  MassTransitStateMachine<MySagaState>
{
    public MySaga()
    {
        InstanceState(x => x.State, Executing, Completed, Failed);
        // 1 = Initial, 2 = Final, 3 = Executing, 4 = Completed
        // 5 - Failed (1 & 2 are built-in states)
    }

    public State Executing { get; private set; }
    public State Completed { get; private set; }
    public State Failed { get; private set; }
    ...
}

score 3 · Accepted Answer · answered Apr 05 '17 at 07:27

The State property indicates the current state machine state. It changes whenever the state machine gets to another state.

It can either be of a complex type State or primitive type string or int. The first case, if you use database persistence, the Name property of the State object will be stored in the database. If you use string (all MassTransit examples suggest this) - it is obvious that the property will contain the state name, representing the state machine property name. If you use int - it is the hardest to understand by looking at the value, since it has come convention like zero is no state, one is the initial state, 2 is the final state and 3 onwards represent all other states.

I would really suggest using string, since it is easier to map and there is no confusion.

So your saga state will look like:

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

you should also configure the state property of the state machine state object in the state machine constructor:

InstanceState(x => x.CurrentState);

Along the execution of this saga, this property will get values Executing, Completed or Failed as you have defined the state properties.

MassTransit Saga State to Instance State Mapping

2 Answers2