state_machine

state_machine adds support for creating state machines for attributes on any Ruby class.

Resources

API

• rdoc.info/projects/pluginaweek/state_machine

Bugs

• pluginaweek.lighthouseapp.com/projects/13288-state_machine

Development

• github.com/pluginaweek/state_machine

Source

• git://github.com/pluginaweek/state_machine.git

Description

State machines make it dead-simple to manage the behavior of a class. Too often, the state of an object is kept by creating multiple boolean attributes and deciding how to behave based on the values. This can become cumbersome and difficult to maintain when the complexity of your class starts to increase.

state_machine simplifies this design by introducing the various parts of a real state machine, including states, events, transitions, and callbacks. However, the api is designed to be so simple you don’t even need to know what a state machine is :)

Some brief, high-level features include:

• Defining state machines on any Ruby class

• Multiple state machines on a single class

• Namespaced state machines

• before/after/around transition hooks with explicit transition requirements

• Integration with ActiveModel, ActiveRecord, DataMapper, MongoMapper, and Sequel

• State predicates

• State-driven instance / class behavior

• State values of any data type

• Dynamically-generated state values

• Event parallelization

• Attribute-based event transitions

• Inheritance

• Internationalization

• GraphViz visualization creator

Examples of the usage patterns for some of the above features are shown below. You can find much more detailed documentation in the actual API.

Usage

Example

Below is an example of many of the features offered by this plugin, including:

• Initial states

• Namespaced states

• Transition callbacks

• Conditional transitions

• State-driven instance behavior

• Customized state values

• Parallel events

Class definition:

classVehicleattr_accessor:seatbelt_on, :time_usedstate_machine:state, :initial=>:parkeddobefore_transition:parked=>any-:parked, :do=>:put_on_seatbeltafter_transition:on=>:crash, :do=>:towafter_transition:on=>:repair, :do=>:fixafter_transitionany=>:parkeddo|vehicle, transition|vehicle.seatbelt_on = falseendaround_transitiondo|vehicle, transition, block|start = Time.nowblock.callvehicle.time_used+=Time.now-startendevent:parkdotransition [:idling, :first_gear] =>:parkedendevent:ignitedotransition:stalled=>same, :parked=>:idlingendevent:idledotransition:first_gear=>:idlingendevent:shift_updotransition:idling=>:first_gear, :first_gear=>:second_gear, :second_gear=>:third_gearendevent:shift_downdotransition:third_gear=>:second_gear, :second_gear=>:first_gearendevent:crashdotransitionall- [:parked, :stalled] =>:stalled, :unless=>:auto_shop_busy?endevent:repairdotransition:stalled=>:parked, :if=>:auto_shop_busy?transition:stalled=>same# Loopback if we have toendstate:parkeddodefspeed0endendstate:idling, :first_geardodefspeed10endendstate:second_geardodefspeed20endendendstate_machine:alarm_state, :initial=>:active, :namespace=>'alarm'doevent:enabledotransitionall=>:activeendevent:disabledotransitionall=>:offendstate:active, :value=>1state:off, :value=>0enddefinitialize@seatbelt_on = false@time_used = 0super() # NOTE: This *must* be called, otherwise states won't get initializedenddefput_on_seatbelt@seatbelt_on = trueenddefauto_shop_busy?falseenddeftow# tow the vehicleenddeffix# get the vehicle fixed by a mechanicendend

Note the comment made on the initialize method in the class. In order for state machine attributes to be properly initialized, super() must be called. See StateMachine::MacroMethods for more information about this.

Using the above class as an example, you can interact with the state machine like so:

vehicle = Vehicle.new# => #<Vehicle:0xb7cf4eac @state="parked", @seatbelt_on=false>vehicle.state# => "parked"vehicle.state_name# => :parkedvehicle.parked?# => truevehicle.can_ignite?# => truevehicle.ignite_transition# => #<StateMachine::Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>vehicle.state_events# => [:ignite]vehicle.state_transitions# => [#<StateMachine::Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>]vehicle.speed# => 0vehicle.ignite# => truevehicle.parked?# => falsevehicle.idling?# => truevehicle.speed# => 10vehicle# => #<Vehicle:0xb7cf4eac @state="idling", @seatbelt_on=true>vehicle.shift_up# => truevehicle.speed# => 10vehicle# => #<Vehicle:0xb7cf4eac @state="first_gear", @seatbelt_on=true>vehicle.shift_up# => truevehicle.speed# => 20vehicle# => #<Vehicle:0xb7cf4eac @state="second_gear", @seatbelt_on=true># The bang (!) operator can raise exceptions if the event failsvehicle.park!# => StateMachine::InvalidTransition: Cannot transition state via :park from :second_gear# Generic state predicates can raise exceptions if the value does not existvehicle.state?(:parked) # => falsevehicle.state?(:invalid) # => IndexError: :invalid is an invalid name# Namespaced machines have uniquely-generated methodsvehicle.alarm_state# => 1vehicle.alarm_state_name# => :activevehicle.can_disable_alarm?# => truevehicle.disable_alarm# => truevehicle.alarm_state# => 0vehicle.alarm_state_name# => :offvehicle.can_enable_alarm?# => truevehicle.alarm_off?# => truevehicle.alarm_active?# => false# Events can be fired in parallelvehicle.fire_events(:shift_down, :enable_alarm) # => truevehicle.state_name# => :first_gearvehicle.alarm_state_name# => :activevehicle.fire_events!(:ignite, :enable_alarm) # => StateMachine::InvalidTransition: Cannot run events in parallel: ignite, enable_alarm

Integrations

In addition to being able to define state machines on all Ruby classes, a set of out-of-the-box integrations are available for some of the more popular Ruby libraries. These integrations add library-specific behavior, allowing for state machines to work more tightly with the conventions defined by those libraries.

The integrations currently available include:

• ActiveModel classes

• ActiveRecord models

• DataMapper resources

• MongoMapper models

• Sequel models

A brief overview of these integrations is described below.

ActiveModel

The ActiveModel integration is useful for both standalone usage and for providing the base implementation for ORMs which implement the ActiveModel API. This integration adds support for validation errors, dirty attribute tracking, and observers. For example,

class Vehicle
include ActiveModel::Dirty
include ActiveModel::Validations
include ActiveModel::Observing
attr_accessor :state
define_attribute_methods [:state]
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |vehicle, transition|
vehicle.seatbelt = 'off'
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end
class VehicleObserver < ActiveModel::Observer
# Callback for :ignite event *before* the transition is performed
def before_ignite(vehicle, transition)
# log message
end
# Generic transition callback *after* the transition is performed
def after_transition(vehicle, transition)
Audit.log(vehicle, transition)
end
end

For more information about the various behaviors added for ActiveModel state machines and how to build new integrations that use ActiveModel, see StateMachine::Integrations::ActiveModel.

ActiveRecord

The ActiveRecord integration adds support for database transactions, automatically saving the record, named scopes, validation errors, and observers. For example,

class Vehicle < ActiveRecord::Base
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |vehicle, transition|
vehicle.seatbelt = 'off'
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end
class VehicleObserver < ActiveRecord::Observer
# Callback for :ignite event *before* the transition is performed
def before_ignite(vehicle, transition)
# log message
end
# Generic transition callback *after* the transition is performed
def after_transition(vehicle, transition)
Audit.log(vehicle, transition)
end
end

For more information about the various behaviors added for ActiveRecord state machines, see StateMachine::Integrations::ActiveRecord.

DataMapper

Like the ActiveRecord integration, the DataMapper integration adds support for database transactions, automatically saving the record, named scopes, Extlib-like callbacks, validation errors, and observers. For example,

class Vehicle
include DataMapper::Resource
property :id, Serial
property :state, String
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |transition|
self.seatbelt = 'off' # self is the record
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end
class VehicleObserver
include DataMapper::Observer
observe Vehicle
# Callback for :ignite event *before* the transition is performed
before_transition :on => :ignite do |transition|
# log message (self is the record)
end
# Generic transition callback *after* the transition is performed
after_transition do |transition|
Audit.log(self, transition) # self is the record
end
around_transition do |transition, block|
# mark start time
block.call
# mark stop time
end
end

Note that the DataMapper::Observer integration is optional and only available when the dm-observer library is installed.

For more information about the various behaviors added for DataMapper state machines, see StateMachine::Integrations::DataMapper.

MongoMapper

The MongoMapper integration adds support for automatically saving the record, basic scopes, validation errors and callbacks. For example,

class Vehicle
include MongoMapper::Document
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |vehicle, transition|
vehicle.seatbelt = 'off' # self is the record
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end

For more information about the various behaviors added for MongoMapper state machines, see StateMachine::Integrations::MongoMapper.

Sequel

Like the ActiveRecord integration, the Sequel integration adds support for database transactions, automatically saving the record, named scopes, validation errors and callbacks. For example,

class Vehicle < Sequel::Model
state_machine :initial => :parked do
before_transition :parked => any - :parked, :do => :put_on_seatbelt
after_transition any => :parked do |transition|
self.seatbelt = 'off' # self is the record
end
around_transition :benchmark
event :ignite do
transition :parked => :idling
end
state :first_gear, :second_gear do
validates_presence_of :seatbelt_on
end
end
def put_on_seatbelt
...
end
def benchmark
...
yield
...
end
end

For more information about the various behaviors added for Sequel state machines, see StateMachine::Integrations::Sequel.

Compatibility

Although state_machine introduces a simplified syntax, it still remains backwards compatible with previous versions and other state-related libraries. For example, transitions and callbacks can continue to be defined like so:

classVehiclestate_machine:initial=>:parkeddobefore_transition:from=>:parked, :except_to=>:parked, :do=>:put_on_seatbeltafter_transition:to=>:parkeddo|transition|self.seatbelt = 'off'# self is the recordendevent:ignitedotransition:from=>:parked, :to=>:idlingendendend

Although this verbose syntax will most likely always be supported, it is recommended that any state machines eventually migrate to the syntax introduced in version 0.6.0.

Tools

Generating graphs

This library comes with built-in support for generating di-graphs based on the events, states, and transitions defined for a state machine using GraphViz. This requires that both the ruby-graphviz gem and graphviz library be installed on the system.

Examples

To generate a graph for a specific file / class:

rake state_machine:draw FILE=vehicle.rb CLASS=Vehicle

To save files to a specific path:

rake state_machine:draw FILE=vehicle.rb CLASS=Vehicle TARGET=files

To customize the image format / orientation:

rake state_machine:draw FILE=vehicle.rb CLASS=Vehicle FORMAT=jpg ORIENTATION=landscape

To generate multiple state machine graphs:

rake state_machine:draw FILE=vehicle.rb,car.rb CLASS=Vehicle,Car

Note that this will generate a different file for every state machine defined in the class. The generated files will use an output filename of the format #{class_name}_#{machine_name}.#{format}.

For examples of actual images generated using this task, see those under the examples folder.

Ruby on Rails Integration

There is a special integration Rake task for generating state machines for classes used in a Ruby on Rails application. This task will load the application environment, meaning that it’s unnecessary to specify the actual file to load.

For example,

rake state_machine:draw CLASS=Vehicle

If you are using this library as a gem in Rails 2.x, the following must be added to the end of your application’s Rakefile in order for the above task to work:

require'tasks/state_machine'

If you are using Rails 3.0+, you must also add the following to your application’s Gemfile:

gem'ruby-graphviz', :require=>'graphviz'

Merb Integration

Like Ruby on Rails, there is a special integration Rake task for generating state machines for classes used in a Merb application. This task will load the application environment, meaning that it’s unnecessary to specify the actual files to load.

For example,

rake state_machine:draw CLASS=Vehicle

Interactive graphs

Jean Bovet’s Visual Automata Simulator is a great tool for “simulating, visualizing and transforming finite state automata and Turing Machines”. It can help in the creation of states and events for your models. It is cross-platform, written in Java.

Testing

To run the core test suite (does not test any of the integrations):

raketest

Test specific versions of integrations like so:

rake test INTEGRATION=active_model VERSION=3.0.0
rake test INTEGRATION=active_record VERSION=2.0.0
rake test INTEGRATION=data_mapper VERSION=0.9.4
rake test INTEGRATION=mongo_mapper VERSION=0.5.5
rake test INTEGRATION=sequel VERSION=2.8.0

Caveats

The following caveats should be noted when using state_machine:

• DataMapper: Attribute-based event transitions are disabled when dm-validations 0.9.4 - 0.9.6 is in use

• Overridden event methods won’t get invoked when using attribute-based event transitions

• around_transition callbacks in ORM integrations won’t work on JRuby since it doesn’t support continuations

Dependencies

• Ruby 1.8.6 or later

If using specific integrations:

• ActiveModel integration: 3.0.0 or later

• ActiveRecord integration: 2.0.0 or later

• DataMapper integration: 0.9.4 or later

• MongoMapper integration: 0.5.5 or later

• Sequel integration: 2.8.0 or later

If graphing state machine:

• ruby-graphviz: 0.9.0 or later