implement orders' common state machine through state_machine or workflow

state_machine.rb

# state_machine: https://github.com/pluginaweek/state_machine

class Order < ActiveRecord::Base
  state_machine :state, initial: :cart do
    before_transition on: :checkout, do: :reduce_buyer_balance
    after_transition on: :dispatch_goods, do: :create_shipping_log
    after_transition on: :confirm, do: :charge_to_seller

    event :checkout do
      transition :cart => :paid
    end

    event :dispatch_goods do
      transition :paid => :shipping
    end

    event :confirm do
      transition :shipping => :finished
    end
  end
end

workflow.rb

# workflow: https://github.com/geekq/workflow

class Order < ActiveRecord::Base
  include Workflow

  workflow do
    state :cart do
      event :checkout, transition_to: :paid
    end

    state :paid do
      event :dispatch_goods, transition_to: :shipping
    end

    state :shipping do
      event :confirm, transition_to: :finished
    end

    state :finished  # this state declaration is required, even that no transition
  end

  def on_cart_exit
    reduce_buyer_balance
  end

  def on_shipping_entry
    create_shipping_log
  end

  def on_finished_entry
    charge_to_seller
  end
end