Workflow Design Dilemma – State Machine, yes or no

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A state machine is a very powerful technique to implement, although I would recommend that you consider a framework called StateLess by Nicholas Blumhardt (Autofaq creator), as it is an amazingly simple implementation of a state machine that avoids the unnecessary complexity of Windows Workflow. His approach avoids the issue of long running workflows being held by a runtime engine, as the state is defined by a simple variable such as a string or int.

Here is a sample state machine:

var phoneCall = new StateMachine<State, Trigger>(State.OffHook);

phoneCall.Configure(State.OffHook)
    .Permit(Trigger.CallDialed, State.Ringing);

phoneCall.Configure(State.Ringing)
    .Permit(Trigger.HungUp, State.OffHook)
    .Permit(Trigger.CallConnected, State.Connected);

phoneCall.Configure(State.Connected)
    .OnEntry(() => StartCallTimer())
    .OnExit(() => StopCallTimer())
    .Permit(Trigger.LeftMessage, State.OffHook)
    .Permit(Trigger.HungUp, State.OffHook)
    .Permit(Trigger.PlacedOnHold, State.OnHold);

// ...

phoneCall.Fire(Trigger.CallDialled);
Assert.AreEqual(State.Ringing, phoneCall.State);

Your state can be an integer which will allow you to feed it the current state from a database. This can be set on the constructor of the state machine as follows:

var stateMachine = new StateMachine<State, Trigger>(
    () => myState.Value,
    s => myState.Value = s);

You can implement this in just one assembly, compared to the multiple projects you need to run Windows Workflow. Maintenance is extremely low, their is no “designer” that generates code for your, etc. Again, it is simple, and there lies the beauty.

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