### Overview [![Build status](https://secure.travis-ci.org/troessner/transitions.png?branch=master)](http://travis-ci.org/troessner/transitions) [![Gem Version](https://badge.fury.io/rb/transitions.png)](http://badge.fury.io/rb/transitions) [![Code Climate](https://codeclimate.com/github/troessner/transitions.png)](https://codeclimate.com/github/troessner/transitions) [![Dependency Status](https://gemnasium.com/troessner/transitions.png)](https://gemnasium.com/troessner/transitions) [![Inline docs](http://inch-ci.org/github/troessner/transitions.png)](http://inch-ci.org/github/troessner/transitions) ### Synopsis `transitions` is a ruby state machine implementation. ### Installation #### Rails This goes into your Gemfile: ```ruby gem "transitions", :require => ["transitions", "active_model/transitions"] ``` … and this into your ORM model: ```ruby include ActiveModel::Transitions ``` #### Standalone ```shell gem install transitions ``` … and this into your class: ```ruby include Transitions ``` ### Using transitions ```ruby class Product include ActiveModel::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, :success => :reorder 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 ``` In this example we assume that you are in a rails project using Bundler, which would automatically require `transitions`. If this is not the case then you have to add ```ruby require 'transitions' ``` wherever you load your dependencies in your application. **Known limitations:** * You can only use one state machine per model. While in theory you can define two or more, this won't work as you would expect. Not supporting this was intentional, if you're interested in the rational look up version 0.1.0 in the CHANGELOG. * Use symbols, not strings for declaring the state machine. Using strings is **not** supported as is using whitespace in names (because `transitions` possibly generates methods out of this). ### Features #### Getting and setting the current state Use the (surprise ahead) `current_state` method - in case you didn't set a state explicitly you'll get back the state that you defined as initial state. ```ruby >> Product.new.current_state => :available ``` You can also set a new state explicitly via `update_current_state(new_state, persist = true / false)` but you should never do this unless you really know what you're doing and why - rather use events / state transitions (see below). Predicate methods are also available using the name of the state. ```ruby >> Product.new.available? => true ``` #### Events When you declare an event, say `discontinue`, three methods are declared for you: `discontinue`, `discontinue!` and `can_discontinue?`. The first two events will modify the `state` attribute on successful transition, but only the bang(!)-version will call `save!`. The `can_discontinue?` method will not modify state but instead returns a boolean letting you know if a given transition is possible. In addition, a `can_transition?` method is added to the object that expects one or more event names as arguments. This semi-verbose method name is used to avoid collisions with [https://github.com/ryanb/cancan](the authorization gem CanCan). ```ruby >> Product.new.can_transition? :out_of_stock => true ``` If you need to get all available transitions for the current state you can simply call: ```ruby >> Product.new.available_transitions => [:discontinued, :out_of_stock] ``` #### Callback overview `transitions` offers you the possibility to define a couple of callbacks during the different stages / places of transitioning from one state to another. So let's say you have an event `discontinue` which transitions the current state from `in_stock` to `sold_out`. The callback sequence would look like this: | discontinue event | | | | | current_state `in_stock` | ----> executes `exit` callback | | | | current_state `in_stock` | ----> executes `on_transition` callback if and only the `guard` check was successfull. If not successfull, the chain aborts here and the `event_failed` callback is executed | | | | current_state `in_stock` | ----> executes `enter` callback for new state `sold_out` | | | | current_state `in_stock` | ----> executes `event_fired` callback | | | | current_state `in_stock` | ----> move state from `in_stock` to `sold_out` | | | | current_state `sold_out` | ----> executes `success` callback of the `discontinue` event This all looks very complicated (I know), but don't worry, in 99% of all cases you don't have to care about the details and the usage itself is straightforward as you can see in the examples below where each callback is explained a little more throrough. #### Callback # 1: State callbacks `enter` and `exit` If you want to trigger a method call when the object enters or exits a state regardless of the transition that made that happen, use `enter` and `exit`. `exit` will be called before the transition out of the state is executed. If you want the method to only be called if the transition is successful, then use another approach. `enter` will be called after the transition has been made but before the object is persisted. If you want the method to only be called after a successful transition to a new state including persistence, use the `success` argument to an event instead. An example: ```ruby class Motor < ActiveRecord::Base include ActiveModel::Transitions state_machine do state :off, enter: :turn_power_off state :on, exit: :prepare_shutdown end end ``` #### Callback # 2: Transition callback `on_transition` Each event definition takes an optional `on_transition` argument, which allows you to execute code on transition. This callback is executed after the `exit` callback of the former state (if it has been defined) but before the `enter` callback of the new state and only if the `guard` check succeeds. There is no check if the callback itself succeeds (meaning that `transitions` does not evaluate its return value somewhere). However, you can easily add some properly abstracted error handling yourself by raising an exception in this callback and then handling this exception in the (also defined by you) `event_failed` callback (see below and / or the wonderful ascii diagram above). You can pass in a Symbol, a String, a Proc or an Array containing method names as Symbol or String like this: ```ruby event :discontinue do transitions :to => :discontinued, :from => [:available, :out_of_stock], :on_transition => [:do_discontinue, :notify_clerk] end ``` Any arguments passed to the event method will be passed on to the `on_transition` callback. #### Callback #3 : Event callback `success` In case you need to trigger a method call after a successful transition you can use `success`. This will be called after the `save!` is complete (if you use the `state_name!` method) and should be used for any methods that require that the object be persisted. ```ruby event :discontinue, :success => :notify_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: ```ruby event :discontinue, :success => lambda { |order| AdminNotifier.notify_about_discontinued_order(order) } do transitions :to => :discontinued, :from => [:available, :out_of_stock] end ``` If you need it, you can even call multiple methods or lambdas just passing an array: ```ruby event :discontinue, :success => [:notify_admin, lambda { |order| AdminNotifier.notify_about_discontinued_order(order) }] do transitions :to => :discontinued, :from => [:available, :out_of_stock] end ``` #### Callback caveats Since callbacks will not be called by you but by `transitions` the scope is different when they are called and you'll run into problems if you use classes / modules in those callbacks that have the same names like `transitions` ones, e.g. "Event": ```Ruby def event_fired(current_state, new_state, event) Event.create! end ``` This will crash because `transitions` uses an Event class as well, and, since the scope has changed when `transitions` calls this method, `transitions` will use it's own Event class here, not yours. In this case you can try to prefix your models with the "::" operator and see if that solves your problems. See https://github.com/troessner/transitions/issues/123 for details. #### 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: ```ruby class Order < ActiveRecord::Base include ActiveModel::Transitions state_machine :auto_scopes => true do state :pick_line_items state :picking_line_items event :move_cart do transitions to: :pick_line_items, from: :picking_line_items end end end ``` you can use this feature a la: ```ruby >> Order.pick_line_items => [] >> Order.create! => # >> Order.pick_line_items => [#] ``` #### Using `guard` Each event definition takes an optional `guard` argument, which acts as a predicate for the transition. You can pass in Symbols, Strings, or Procs like this: ```ruby event :discontinue do transitions :to => :discontinued, :from => [:available, :out_of_stock], :guard => :can_discontinue end ``` or ```ruby event :discontinue do transitions :to => :discontinued, :from => [:available, :out_of_stock], :guard => [:can_discontinue, :super_sure?] end ``` Any arguments passed to the event method will be passed on to the `guard` predicate. Note that guards will **not** raise on failure on their own. This means that if you want to treat the failure of a guard exceptional you'll need to raise an exception yourself explicitly in that guard (see [here](https://github.com/troessner/transitions/issues/149) for the corresponding discussion). #### 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* ```ruby # 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 transitions :from => :exploded, :to => :rebuilt end ``` #### Using `event_fired` and `event_failed` In case you define `event_fired` and / or `event_failed`, `transitions` will use those callbacks correspondingly. You can use those callbacks like this: ```ruby def event_fired(current_state, new_state, event) MyLogger.info "Event fired #{event.inspect}" end def event_failed(event) MyLogger.warn "Event failed #{event.inspect}" end ``` #### Listing all the available states and events You can easily get a listing of all available states: ```ruby Order.available_states # Uses the default state machine # => [:pick_line_items, :picking_line_items] ``` Same goes for the available events: ```ruby Order.available_events # => [:move_cart] ``` #### Explicitly setting the initial state with the `initial` option ```ruby state_machine :initial => :closed do state :open state :closed end ``` The explicitly specified state **must** be one of the states listed in the state definition below, otherwise `transitions` will raise a rather unhelpful exception like "NoMethodError: undefined method `call_action' for nil:NilClass" (there's a ticket to fix this already: https://github.com/troessner/transitions/issues/112) ### Configuring a different column name with ActiveRecord To use a different column than `state` to track it's value simply do this: ```ruby class Product < ActiveRecord::Base include Transitions state_machine :attribute_name => :different_column do ... end end ``` ### Ruby Compatibility Supported versions: * 2.1 * 2.2 Supported implementations: * MRI * Rubinius * Jruby ### Supported Rails versions: * 3 * 4 ### Known bugs / limitations * Right now it seems like `transitions` does not play well with `mongoid`. A possible fix had to be rolled back due to other side effects: https://github.com/troessner/transitions/issues/76. Since I know virtually zero about mongoid, a pull request would be highly appreciated. * Multiple state machines are not and will not be supported. For the rationale behind this see the Changelog. ### Documentation, Guides & Examples * [Online API Documentation](http://rdoc.info/github/troessner/transitions/master/Transitions) * [Railscasts #392: A Tour of State Machines](http://railscasts.com/episodes/392-a-tour-of-state-machines) (requires Pro subscription) ### Copyright Copyright (c) 2010 Jakub Kuźma, Timo Rößner. See LICENSE for details.