📦 statesman/ gocardless

Installation

To get started, just add Statesman to your Gemfile, and then run bundle:

gem 'statesman', '~> 13.0.0'

Usage

First, create a state machine based on Statesman::Machine:

class OrderStateMachine
  include Statesman::Machine

  state :pending, initial: true
  state :checking_out
  state :purchased
  state :shipped
  state :cancelled
  state :failed
  state :refunded

  transition from: :pending,      to: [:checking_out, :cancelled]
  transition from: :checking_out, to: [:purchased, :cancelled]
  transition from: :purchased,    to: [:shipped, :failed]
  transition from: :shipped,      to: :refunded

  guard_transition(to: :checking_out) do |order|
    order.products_in_stock?
  end

  before_transition(from: :checking_out, to: :cancelled) do |order, transition|
    order.reallocate_stock
  end

  before_transition(to: :purchased) do |order, transition|
    PaymentService.new(order).submit
  end

  after_transition(to: :purchased) do |order, transition|
    MailerService.order_confirmation(order).deliver
  end
end

Then, link it to your model:

class Order < ActiveRecord::Base
  has_many :order_transitions, autosave: false

  include Statesman::Adapters::ActiveRecordQueries[
    transition_class: OrderTransition,
    initial_state: :pending
  ]

  def state_machine
    @state_machine ||= OrderStateMachine.new(self, transition_class: OrderTransition)
  end
end

Next, you'll need to create a further model to represent state transitions:

class OrderTransition < ActiveRecord::Base
  include Statesman::Adapters::ActiveRecordTransition

  validates :to_state, inclusion: { in: OrderStateMachine.states }

  belongs_to :order, inverse_of: :order_transitions
end

Now, you can start working with your state machine:

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