mhayes / transitions

State machine extracted from ActiveModel

Travis Build Status ¶ ↑

<img src=“https://secure.travis-ci.org/troessner/transitions.png”/>

Synopsis¶ ↑

‘transitions` is a ruby state machine implementation.

Installation¶ ↑

Rails¶ ↑

This goes into your Gemfile:

gem "transitions", :require => ["transitions", "active_record/transitions"]

… and this into your AR model:

include ActiveRecord::Transitions

Standalone¶ ↑

gem install transitions

Using transitions¶ ↑

require 'transitions'

class Product
  include Transitions

  state_machine do
    state :available # first one is initial state
    state :out_of_stock, :exit => :exit_out_of_stock
    state :discontinued, :enter => lambda { |product| product.cancel_orders }

    event :discontinued do
      transitions :to => :discontinued, :from => [:available, :out_of_stock], :on_transition => :do_discontinue
    end
    event :out_of_stock do
      transitions :to => :out_of_stock, :from => [:available, :discontinued]
    end
    event :available do
      transitions :to => :available, :from => [:out_of_stock], :guard => lambda { |product| product.in_stock > 0 }
    end
  end
end

Features¶ ↑

Events¶ ↑

When you declare an event, say discontinue, two methods are declared for you: discontinue and discontinue!. Both events will call write_state_without_persistence on successful transition, but only the bang(!)-version will call write_state.

Automatic scope generation¶ ↑

‘transitions` will automatically generate scopes for you if you are using ActiveRecord and tell it to do so via the `auto_scopes` option:

Given a model like this:

class Order < ActiveRecord::Base
  include ActiveRecord::Transitions
  state_machine :auto_scopes => true do
    state :pick_line_items
    state :picking_line_items
  end
end

you can use this feature a la:

>> Order.pick_line_items
=> []
>> Order.create!
=> #<Order id: 3, state: "pick_line_items", description: nil, created_at: "2011-08-23 15:48:46", updated_at: "2011-08-23 15:48:46">
>> Order.pick_line_items
=> [#<Order id: 3, state: "pick_line_items", description: nil, created_at: "2011-08-23 15:48:46", updated_at: "2011-08-23 15:48:46">]

Using ‘on_transition`¶ ↑

Each event definition takes an optional “on_transition” argument, which allows you to execute methods on transition. You can pass in a Symbol, a String, a Proc or an Array containing method names as Symbol or String like this:

event :discontinue do
  transitions :to => :discontinued, :from => [:available, :out_of_stock], :on_transition => [:do_discontinue, :notify_clerk]
end

Using ‘success`¶ ↑

In case you need to trigger a method call after a successful transition you can use ‘success`:

event :discontinue, :success => :notfiy_admin do
  transitions :to => :discontinued, :from => [:available, :out_of_stock]
end

In addition to just specify the method name on the record as a symbol you can pass a lambda to perfom some more complex success callbacks:

event :discontinue, :success => lambda { |order) AdminNotifier.notify_about_discontinued_order(order) } do
  transitions :to => :discontinued, :from => [:available, :out_of_stock]
end

Timestamps¶ ↑

If you’d like to note the time of a state change, Transitions comes with timestamps free! To activate them, simply pass the :timestamp option to the event definition with a value of either true or the name of the timestamp column. *NOTE - This should be either true, a String or a Symbol*

# This will look for an attribute called exploded_at or exploded_on (in that order)
# If present, it will be updated
event :explode, :timestamp => true do
  transitions :from => :complete, :to => :exploded
end

# This will look for an attribute named repaired_on to update upon save
event :rebuild, :timestamp => :repaired_on do
  transiions :from => :exploded, :to => :rebuilt
end

Listing all the available states¶ ↑

You can easily get a listing of all available states:

Order.available_states # Uses the `default` state machine
# => [:pick_line_items, :picking_line_items]

In case you have multiple state machines you can also pass the state machine name:

Order.available_states(:your_machine)

Documentation, Guides & Examples¶ ↑

• Online API Documentation

• Krzysiek Heród (aka Netizer) wrote a nice blog post about using Transitions in ActiveRecord.

Copyright¶ ↑

Copyright © 2010 Jakub Kuźma, Timo Rößner. See LICENSE for details.