How do you model state_machine style transitions?

[markquezada]

Hi, I just came across Statesman and it looks awesome.

This is more of a question than a bug, but I didn't know where else to ask. I'm trying out Statesman by converting an old project that used the state_machine gem. A common pattern used with that gem is to define several transitions on an event like so:

    event :deliver do
      # The first transition that matches the state and passes its conditions
      # will be used
      transition :pending => :delivered, :if => :deliver_text_message
      transition :pending => :delivery_failed
    end

The key point being that you can define a transition for what happens if deliver_text_message fails.

I can't quite figure out how to model something like this with Statesman since all transitions are defined by their "from" and "to" states, not with an explicit "event" like in state_machine. The only thing I can think of is that you're deliberately pushing this type of functionality up the stack into a service object, or the like.

I'm curious how you're modeling something like this where state transition is dependent on say, an API's return value?

[iurimatias]

#63

[gogiel]

#63 doesn't solve the problem. It's not possible to make two transitions from one state in a single event,. The only way now is to implement "event" method manually with branching statement. @mrappleton what do you think about adding :if statement to transition method?

[isaacseymour]

I believe #78 would allow you to put a guard on the transition from: :pending, to: :delivered which passes only when deliver_text_message is true. Then the first acceptable transition would be performed, which I think is the desired effect?

[markquezada]

@isaacseymour Yes, that's exactly what I'd hope to happen. That's the only issue keeping me from using statesman on our project right now.

[isaacseymour]

@markquezada we've discussed adding this kind of behaviour to Statesman in the office and decided it goes against the underlying philosophy of the gem - see [this comment[(https://github.com//pull/78#issuecomment-56190184). We think this behaviour belongs in your controller, or something like a MessageDeliveryService.

[markquezada]

I've added some comments directly on that pull request.

[jackfranklin]

Most of the discussion on this is now in #78 (comment), so I'm going to close this.