Mike Owens

Rails State Machine

I think it’s crazy when I implement something that “Surely, I’m the only one that’ll ever use this”, and then another implementation ends up in Rails proper. Last year, I wrote acts_as_fsm; a state machine implementation for ActiveRecord models:

SaleMachine = Fsm::state_machine do
  state :new    => :queued
  state :queued => :new

  state :queued => :on_site do |sale, old, new|
    sale.started_at = Time.now
  end

  state :on_site => :processing_orders do |sale, old, new|

    sale.ended_at = Time.now
    sale.orders.each do |o|
      o.status_items <<
        OrderStatusItem.new(:status  => "CLOSE_WAIT",
                            :message => "Sale ended.  Waiting for a few stragglers" );
      o.save!
    end
  end

  state :processing_orders => :shipped
end

And then, to use the machine:

class Sale < ActiveRecord::Base
  acts_as_fsm :machine => SaleMachine
end

There is nothing I love more than throwing away code I wrote and migrating to something in the framework. Less stuff for me to maintain. Check out ActiveRecord::StateMachine.