How to encapsulate .NET Stateless state machine

Question

I have a project where there is a mostly linear workflow. I\'m attempting to use the .NET Stateless library to act as workflow engine/state machine. The number of examples out

Answer 1

This is how I achieved it in my project.

Separated workflow logic to separate class. I had couple of workflows based on one of the flags present in the request object; below is one of the workflow classes:

public class NationalWorkflow : BaseWorkflow
{
    public NationalWorkflow(SwiftRequest request) : this(request, Objects.RBDb)
    { }

    public NationalWorkflow(SwiftRequest request, RBDbContext dbContext)
    {
        this.request = request;
        this.dbContext = dbContext;
        this.ConfigureWorkflow();
    }

    protected override void ConfigureWorkflow()
    {
        workflow = new StateMachine<SwiftRequestStatus, SwiftRequestTriggers>(
           () => request.SwiftRequestStatus, state => request.SwiftRequestStatus = state);

        workflow.OnTransitioned(Transitioned);

        workflow.Configure(SwiftRequestStatus.New)
            .OnEntry(NotifyRequestCreation)
            .Permit(SwiftRequestTriggers.ProcessRequest, SwiftRequestStatus.InProgress);

        workflow.Configure(SwiftRequestStatus.InProgress)
            .OnEntry(ValidateRequestEligibility)
            .Permit(SwiftRequestTriggers.AutoApprove, SwiftRequestStatus.Approved)
            .Permit(SwiftRequestTriggers.AdvancedServicesReview, SwiftRequestStatus.PendingAdvancedServices);

.....................
}

Which is triggered from the controller/any other layer:

private static void UpdateRequest(SwiftRequestDTO dtoRequest)
    {
            var workflow = WorkflowFactory.Get(request);
            workflow.UpdateRequest();
    }

As mentioned above, I had different workflow rules based on conditions in the request object and hence used a factory pattern WorkflowFactory.Get(request); you may create an instance of your workflow/inject it as desired

And inside the workflow class (BaseWorkflow class in my case), I have exposed the actions:

    public void UpdateRequest()
    {
        using (var trans = this.dbContext.Database.BeginTransaction())
        {
            this.actionComments = "Updating the request";
            this.TryFire(SwiftRequestTriggers.Update);

            SaveChanges();
            trans.Commit();
        }
    }

  protected void TryFire(SwiftRequestTriggers trigger)
    {
        if (!workflow.CanFire(trigger))
        {
            throw new Exception("Cannot fire " + trigger.ToString() + " from state- " + workflow.State);
        }
        workflow.Fire(trigger);
    }

Answer 2

There is an article by Scott Hanselman with an example and introduction to a library. Also there few examples available on their GitHub including Bug implementation example mentioned in Scott's article that encapsulates the state machine.

Below is an example of how the state can be extracted from behavior:

public class PatientRegistrationState
{
    private StateMachine<WorkflowState, WorkflowTrigger> stateMachine;
    private StateMachine<WorkflowState, WorkflowStateTrigger>.TriggerWithParameters<DateTime> registrationTrigger;

    public PatientRegistrationState(State initialState = default(State)) {
        stateMachine = new StateMachine<WorkflowState, WorkflowTrigger>(initialState);

        stateMachine.Configure(WorkflowState.Unregistered)
            .Permit(WorkflowTrigger.Register, WorkflowStateType.Registered);

        stateMachine.Configure(WorkflowState.Registered)
            .Permit(WorkflowTrigger.ScheduleSampling, WorkflowState.SamplingScheduled)
            .OnEntryFrom(registrationTrigger, (date) => OnPatientRegistered(date));
    }

    public WorkflowState State => stateMachine.State;
    public Action<DateTime> OnPatientRegistered {get; set;} = (date) => { };

    // For state changes that do not require parameters.
    public void ChangeTo(WorkflowTrigger trigger)
    {
        stateMachine.Fire<DateTime>(trigger);
    }

    // For state changes that require parameters.
    public void ChangeToRegistered(DateTime dateOfBirth)
    {
        stateMachine.Fire<DateTime>(registrationTrigger, dateOfBirth);        
    }

    // Change to other states that require parameters...
}

public class PatientRegistration
{
    private PatientRegistrationState registrationState;
    private Patient patient;

    public PatientRegistration()
    {
        registrationState = PatientRegistrationState(WorkflowState.Unregistered)
        {
            OnPatientRegistered = RegisterPatient;
        }
    }

    public Patient RegisterPatient(DateTime dateOfBirth)
    {
        registrationState.ChangeToRegistered(dateOfBirth);
        logger.Info("State changed to: " + registrationState.State);
        return patient;
    }

    private void RegisterPatient(DateTime dateOfBirth)
    {
        // Registration code
    }
}