Rollback persisted finite machine: An example

work_request.rb

class WorkRequest < ActiveRecord::Base

  # Attributes include :state_history (text) and :state (string)

  serialize :state_history, Array

  after_find :restore_process
  after_initialize :restore_process

  def rollback_state_to_previous
    previous_state = state_history.pop
    return unless previous_state
    process.restore! previous_state.to_sym
    self.state = previous_state
    save
  end

  def process
    @process ||= new_process
  end
  delegate :request, :submit, to: :process

  private
  def new_process
    new_process = WorkRequestProcess.new
    new_process.target(self)
    new_process
  end

  def restore_process
    process.restore!(state.to_sym) if state.present?
  end

end

work_request_process.rb

class WorkRequestProcess < FiniteMachine::Definition
  
  initial :draft

  alias_target :work_request

  events {

    event :request, {
      :draft => :requested
    }
    event :submit, {
      :requested => :submitted
    }
    
  }

  callbacks {
    on_transition do |event|
      work_request.state = event.to
      work_request.state_history << event.from
      work_request.save
    end
  }

end

A work request starts in the draft state. To move to the next state:

work_request.request

This triggers the request event and the new state is stored in work_request#state, and the previous state is added to state_history

work_request.state               == 'requested'
work_request.state_history  == ['draft']

The work request can then be progressed to the next state:

work_request.submit

Which changes the stored attributes to:

work_request.state               == 'submitted'
work_request.state_history  == ['draft', 'requested']

To roll back:

work_request.rollback_state_to_previous

Which returns the stored attributes to:

work_request.state               == 'requested'
work_request.state_history  == ['draft']