state_machine

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

Resources

API

http://rdoc.info/github/pluginaweek/state_machine/master/frames

Bugs

http://github.com/pluginaweek/state_machine/issues

Development

http://github.com/pluginaweek/state_machine

Testing

http://travis-ci.org/pluginaweek/state_machine

Source

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

Mailing List

http://groups.google.com/group/pluginaweek-talk

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/failure transition hooks with explicit transition requirements
Integration with ActiveModel, ActiveRecord, DataMapper, Mongoid, 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
Path analysis
Inheritance
Internationalization
GraphViz visualization creator
YARD integration (Ruby 1.9+ only)
Flexible machine syntax

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
Path analysis

Class definition:

class Vehicle
  attr_accessor :seatbelt_on, :time_used, :auto_shop_busy
  
  state_machine :state, :initial => :parked do
    before_transition :parked => any - :parked, :do => :put_on_seatbelt
    
    after_transition :on => :crash, :do => :tow
    after_transition :on => :repair, :do => :fix
    after_transition any => :parked do |vehicle, transition|
      vehicle.seatbelt_on = false
    end
    
    after_failure :on => :ignite, :do => :log_start_failure
    
    around_transition do |vehicle, transition, block|
      start = Time.now
      block.call
      vehicle.time_used += Time.now - start
    end
    
    event :park do
      transition [:idling, :first_gear] => :parked
    end
    
    event :ignite do
      transition :stalled => same, :parked => :idling
    end
    
    event :idle do
      transition :first_gear => :idling
    end
    
    event :shift_up do
      transition :idling => :first_gear, :first_gear => :second_gear, :second_gear => :third_gear
    end
    
    event :shift_down do
      transition :third_gear => :second_gear, :second_gear => :first_gear
    end
    
    event :crash do
      transition all - [:parked, :stalled] => :stalled, :if => lambda {|vehicle| !vehicle.passed_inspection?}
    end
    
    event :repair do
      # The first transition that matches the state and passes its conditions
      # will be used
      transition :stalled => :parked, :unless => :auto_shop_busy
      transition :stalled => same
    end
    
    state :parked do
      def speed
        0
      end
    end
    
    state :idling, :first_gear do
      def speed
        10
      end
    end
    
    state all - [:parked, :stalled, :idling] do
      def moving?
        true
      end
    end
    
    state :parked, :stalled, :idling do
      def moving?
        false
      end
    end
  end
  
  state_machine :alarm_state, :initial => :active, :namespace => 'alarm' do
    event :enable do
      transition all => :active
    end
    
    event :disable do
      transition all => :off
    end
    
    state :active, :value => 1
    state :off, :value => 0
  end
  
  def initialize
    @seatbelt_on = false
    @time_used = 0
    @auto_shop_busy = true
    super() # NOTE: This *must* be called, otherwise states won't get initialized
  end
  
  def put_on_seatbelt
    @seatbelt_on = true
  end
  
  def passed_inspection?
    false
  end
  
  def tow
    # tow the vehicle
  end
  
  def fix
    # get the vehicle fixed by a mechanic
  end
  
  def log_start_failure
    # log a failed attempt to start the vehicle
  end
end

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              # => :parked
vehicle.human_state_name        # => "parked"
vehicle.parked?                 # => true
vehicle.can_ignite?             # => true
vehicle.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                   # => 0
vehicle.moving?                 # => false

vehicle.ignite                  # => true
vehicle.parked?                 # => false
vehicle.idling?                 # => true
vehicle.speed                   # => 10
vehicle                         # => #<Vehicle:0xb7cf4eac @state="idling", @seatbelt_on=true>

vehicle.shift_up                # => true
vehicle.speed                   # => 10
vehicle.moving?                 # => true
vehicle                         # => #<Vehicle:0xb7cf4eac @state="first_gear", @seatbelt_on=true>

# A generic event helper is available to fire without going through the event's instance method
vehicle.fire_state_event(:shift_up) # => true

# Call state-driven behavior that's undefined for the state raises a NoMethodError
vehicle.speed                   # => NoMethodError: super: no superclass method `speed' for #<Vehicle:0xb7cf4eac>
vehicle                         # => #<Vehicle:0xb7cf4eac @state="second_gear", @seatbelt_on=true>

# The bang (!) operator can raise exceptions if the event fails
vehicle.park!                   # => StateMachine::InvalidTransition: Cannot transition state via :park from :second_gear

# Generic state predicates can raise exceptions if the value does not exist
vehicle.state?(:parked)         # => false
vehicle.state?(:invalid)        # => IndexError: :invalid is an invalid name

# Namespaced machines have uniquely-generated methods
vehicle.alarm_state             # => 1
vehicle.alarm_state_name        # => :active

vehicle.can_disable_alarm?      # => true
vehicle.disable_alarm           # => true
vehicle.alarm_state             # => 0
vehicle.alarm_state_name        # => :off
vehicle.can_enable_alarm?       # => true

vehicle.alarm_off?              # => true
vehicle.alarm_active?           # => false

# Events can be fired in parallel
vehicle.fire_events(:shift_down, :enable_alarm) # => true
vehicle.state_name                              # => :first_gear
vehicle.alarm_state_name                        # => :active

vehicle.fire_events!(:ignite, :enable_alarm)    # => StateMachine::InvalidTransition: Cannot run events in parallel: ignite, enable_alarm

# Human-friendly names can be accessed for states/events
Vehicle.human_state_name(:first_gear)               # => "first gear"
Vehicle.human_alarm_state_name(:active)             # => "active"

Vehicle.human_state_event_name(:shift_down)         # => "shift down"
Vehicle.human_alarm_state_event_name(:enable)       # => "enable"

# States / events can also be references by the string version of their name
Vehicle.human_state_name('first_gear')              # => "first gear"
Vehicle.human_state_event_name('shift_down')        # => "shift down"

# Available transition paths can be analyzed for an object
vehicle.state_paths                                       # => [[#<StateMachine::Transition ...], [#<StateMachine::Transition ...], ...]
vehicle.state_paths.to_states                             # => [:parked, :idling, :first_gear, :stalled, :second_gear, :third_gear]
vehicle.state_paths.events                                # => [:park, :ignite, :shift_up, :idle, :crash, :repair, :shift_down]

# Find all paths that start and end on certain states
vehicle.state_paths(:from => :parked, :to => :first_gear) # => [[
                                                          #       #<StateMachine::Transition attribute=:state event=:ignite from="parked" ...>,
                                                          #       #<StateMachine::Transition attribute=:state event=:shift_up from="idling" ...>
                                                          #    ]]
# Skipping state_machine and writing to attributes directly
vehicle.state = "parked"
vehicle.state                   # => "parked"
vehicle.state_name              # => :parked

# *Note* that the following is not supported (see StateMachine::MacroMethods#state_machine):
# vehicle.state = :parked

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
Mongoid models
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
  
  # Generic callback after the transition fails to perform
  def after_failure_to_transition(vehicle, transition)
    Audit.error(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
  
  # Generic callback after the transition fails to perform
  after_transition_failure do |transition|
    Audit.log(self, transition) # self is the record
  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.

Mongoid

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

class Vehicle
  include Mongoid::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

class VehicleObserver < Mongoid::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 Mongoid state machines, see StateMachine::Integrations::Mongoid.

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
  plugin :validation_class_methods
  
  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.

Additional Topics

Explicit vs. Implicit Event Transitions

Every event defined for a state machine generates an instance method on the class that allows the event to be explicitly triggered. Most of the examples in the state_machine documentation use this technique. However, with some types of integrations, like ActiveRecord, you can also implicitly fire events by setting a special attribute on the instance.

Suppose you're using the ActiveRecord integration and the following model is defined:

class Vehicle < ActiveRecord::Base
  state_machine :initial => :parked do
    event :ignite do
      transition :parked => :idling
    end
  end
end

To trigger the ignite event, you would typically call the Vehicle#ignite method like so:

vehicle = Vehicle.create    # => #<Vehicle id=1 state="parked">
vehicle.ignite              # => true
vehicle.state               # => "idling"

This is referred to as an explicit event transition. The same behavior can also be achieved implicitly by setting the state event attribute and invoking the action associated with the state machine. For example:

vehicle = Vehicle.create        # => #<Vehicle id=1 state="parked">
vehicle.state_event = "ignite"  # => "ignite"
vehicle.save                    # => true
vehicle.state                   # => "idling"
vehicle.state_event             # => nil

As you can see, the ignite event was automatically triggered when the save action was called. This is particularly useful if you want to allow users to drive the state transitions from a web API.

See each integration's API documentation for more information on the implicit approach.

Symbols vs. Strings

In all of the examples used throughout the documentation, you'll notice that states and events are almost always referenced as symbols. This isn't a requirement, but rather a suggested best practice.

You can very well define your state machine with Strings like so:

class Vehicle
  state_machine :initial => 'parked' do
    event 'ignite' do
      transition 'parked' => 'idling'
    end
    
    # ...
  end
end

You could even use numbers as your state / event names. The important thing to keep in mind is that the type being used for referencing states / events in your machine definition must be consistent. If you're using Symbols, then all states / events must use Symbols. Otherwise you'll encounter the following error:

class Vehicle
  state_machine do
    event :ignite do
      transition :parked => 'idling'
    end
  end
end

# => ArgumentError: "idling" state defined as String, :parked defined as Symbol; all states must be consistent

There is an exception to this rule. The consistency is only required within the definition itself. However, when the machine's helper methods are called with input from external sources, such as a web form, state_machine will map that input to a String / Symbol. For example:

class Vehicle
  state_machine :initial => :parked do
    event :ignite do
      transition :parked => :idling
    end
  end
end

v = Vehicle.new     # => #<Vehicle:0xb71da5f8 @state="parked">
v.state?('parked')  # => true
v.state?(:parked)   # => true

Note that none of this actually has to do with the type of the value that gets stored. By default, all state values are assumed to be string -- regardless of whether the state names are symbols or strings. If you want to store states as symbols instead you'll have to be explicit about it:

class Vehicle
  state_machine :initial => :parked do
    event :ignite do
      transition :parked => :idling
    end
    
    states.each do |state|
      self.state(state.name, :value => state.name.to_sym)
    end
  end
end

v = Vehicle.new     # => #<Vehicle:0xb71da5f8 @state=:parked>
v.state?('parked')  # => true
v.state?(:parked)   # => true

Syntax flexibility

Although state_machine introduces a simplified syntax, it still remains backwards compatible with previous versions and other state-related libraries by providing some flexibility around how transitions are defined. See below for an overview of these syntaxes.

Verbose syntax

In general, it's recommended that state machines use the implicit syntax for transitions. However, you can be a little more explicit and verbose about transitions by using the :from, :except_from, :to, and :except_to options.

For example, transitions and callbacks can be defined like so:

class Vehicle
  state_machine :initial => :parked do
    before_transition :from => :parked, :except_to => :parked, :do => :put_on_seatbelt
    after_transition :to => :parked do |transition|
      self.seatbelt = 'off' # self is the record
    end
    
    event :ignite do
      transition :from => :parked, :to => :idling
    end
  end
end

Transition context

Some flexibility is provided around the context in which transitions can be defined. In almost all examples throughout the documentation, transitions are defined within the context of an event. If you prefer to have state machines defined in the context of a state either out of preference or in order to easily migrate from a different library, you can do so as shown below:

class Vehicle
  state_machine :initial => :parked do
    ...
    
    state :parked do
      transition :to => :idling, :on => [:ignite, :shift_up], :if => :seatbelt_on?
      
      def speed
        0
      end
    end
    
    state :first_gear do
      transition :to => :second_gear, :on => :shift_up
      
      def speed
        10
      end
    end
    
    state :idling, :first_gear do
      transition :to => :parked, :on => :park
    end
  end
end

In the above example, there's no need to specify the from state for each transition since it's inferred from the context.

You can also define transitions completely outside the context of a particular state / event. This may be useful in cases where you're building a state machine from a data store instead of part of the class definition. See the example below:

class Vehicle
  state_machine :initial => :parked do
    ...
    
    transition :parked => :idling, :on => [:ignite, :shift_up]
    transition :first_gear => :second_gear, :second_gear => :third_gear, :on => :shift_up
    transition [:idling, :first_gear] => :parked, :on => :park
    transition [:idling, :first_gear] => :parked, :on => :park
    transition all - [:parked, :stalled] => :stalled, :unless => :auto_shop_busy?
  end
end

Notice that in these alternative syntaxes:

You can continue to configure :if and :unless conditions
You can continue to define from states (when in the machine context) using the all, any, and same helper methods

Static / Dynamic definitions

In most cases, the definition of a state machine is static. That is to say, the states, events and possible transitions are known ahead of time even though they may depend on data that's only known at runtime. For example, certain transitions may only be available depending on an attribute on that object it's being run on. All of the documentation in this library define static machines like so:

class Vehicle
  state_machine :state, :initial => :parked do
    event :park do
      transition [:idling, :first_gear] => :parked
    end
    
    ...
  end
end

However, there may be cases where the definition of a state machine is dynamic. This means that you don't know the possible states or events for a machine until runtime. For example, you may allow users in your application to manage the state machine of a project or task in your system. This means that the list of transitions (and their associated states / events) could be stored externally, such as in a database. In a case like this, you can define dynamically-generated state machines like so:

class Vehicle
  attr_accessor :state
  
  # Make sure the machine gets initialized so the initial state gets set properly
  def initialize(*)
    super
    machine
  end
  
  # Replace this with an external source (like a db)
  def transitions
    [
      {:parked => :idling, :on => :ignite},
      {:idling => :first_gear, :first_gear => :second_gear, :on => :shift_up}
      # ...
    ]
  end
  
  # Create a state machine for this vehicle instance dynamically based on the
  # transitions defined from the source above
  def machine
    vehicle = self
    @machine ||= Machine.new(vehicle, :initial => :parked, :action => :save) do
      vehicle.transitions.each {|attrs| transition(attrs)}
    end
  end
  
  def save
    # Save the state change...
    true
  end
end

# Generic class for building machines
class Machine
  def self.new(object, *args, &block)
    machine_class = Class.new
    machine = machine_class.state_machine(*args, &block)
    attribute = machine.attribute
    action = machine.action
    
    # Delegate attributes
    machine_class.class_eval do
      define_method(:definition) { machine }
      define_method(attribute) { object.send(attribute) }
      define_method("#{attribute}=") {|value| object.send("#{attribute}=", value) }
      define_method(action) { object.send(action) } if action
    end
    
    machine_class.new
  end
end

vehicle = Vehicle.new                   # => #<Vehicle:0xb708412c @state="parked" ...>
vehicle.state                           # => "parked"
vehicle.machine.ignite                  # => true
vehicle.machine.state                   # => "idling
vehicle.state                           # => "idling"
vehicle.machine.state_transitions       # => [#<StateMachine::Transition ...>]
vehicle.machine.definition.states.keys  # => :first_gear, :second_gear, :parked, :idling

As you can see, state_machine provides enough flexibility for you to be able to create new machine definitions on the fly based on an external source of transitions.

Core Extensions

By default, state_machine extends the Ruby core with a state_machine method on Class. All other parts of the library are confined within the StateMachine namespace. While this isn't wholly necessary, it also doesn't have any performance impact and makes it truly feel like an extension to the language. This is very similar to the way that you'll find yaml, json, or other libraries adding a simple method to all objects just by loading the library.

However, if you'd like to avoid having state_machine add this extension to the Ruby core, you can do so like so:

require 'state_machine/core'

class Vehicle
  extend StateMachine::MacroMethods
  
  state_machine do
    # ...
  end
end

If you're using a gem loader like Bundler, you can explicitly indicate which file to load:

# In Gemfile
...
gem 'state_machine', :require => 'state_machine/core'

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

See http://rdoc.info/github/glejeune/Ruby-Graphviz/Constants for the list of supported image formats. If resolution is an issue, the svg format may offer better results.

To generate multiple state machine graphs:

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

To use human state / event names:

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

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.

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.

Generating documentation

If you use YARD to generate documentation for your projects, state_machine can be enabled to generate API docs for auto-generated methods from each state machine definition as well as providing embedded visualizations.

See the generated API documentation under the examples folder to see what the output looks like.

To enable the YARD integration, you'll need to add state_machine to the list of YARD's plugins by editing the global YARD config:

~/.yard/config:

load_plugins: true
autoload_plugins:
  - state_machine

Once enabled, simply generate your documentation like you normally do.

Note that this only works for Ruby 1.9+.

Web Frameworks

Ruby on Rails

Integrating state_machine into your Ruby on Rails application is straightforward and provides a few additional features specific to the framework. To get started, following the steps below.

1. Install the gem

If using Rails 2.x:

# In config/environment.rb
...
Rails::Initializer.run do |config|
  ...
  config.gem 'state_machine', :version => '~> 1.0'
  ...
end

If using Rails 3.x or up:

# In Gemfile
...
gem 'state_machine'
gem 'ruby-graphviz', :require => 'graphviz' # Optional: only required for graphing

As usual, run bundle install to load the gems.

2. Create a model

Create a model with a field to store the state, along with other any other fields your application requires:

$ rails generate model Vehicle state:string
$ rake db:migrate

3. Configure the state machine

Add the state machine to your model. Following the examples above, app/models/vehicle.rb might become:

class Vehicle < ActiveRecord::Base
  state_machine :initial => :parked do
    before_transition :parked => any - :parked, :do => :put_on_seatbelt
    ...
  end
end

Rake tasks

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'

Merb

Rake tasks

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

Testing

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

bundle install
bundle exec rake test

To run integration tests:

bundle install
rake appraisal:install
rake appraisal:test

You can also test a specific version:

rake appraisal:active_model-3.0.0 test
rake appraisal:active_record-2.0.0 test
rake appraisal:data_mapper-0.9.4 test
rake appraisal:mongoid-2.0.0 test
rake appraisal:mongo_mapper-0.5.5 test
rake appraisal:sequel-2.8.0 test

Caveats

The following caveats should be noted when using state_machine:

Overridden event methods won't get invoked when using attribute-based event transitions
DataMapper: Attribute-based event transitions are disabled when using dm-validations 0.9.4 - 0.9.6
DataMapper: Transitions cannot persist states when run from after :create / :save callbacks
JRuby / Rubinius: around_transition callbacks in ORM integrations won't work on JRuby since it doesn't support continuations
Factory Girl: Dynamic initial states don't work because of the way factory_girl builds objects. You can work around this in a few ways:
1. Use a default state that is common across all objects and rely on events to determine the actual initial state for your object.
2. Assuming you're not using state-driven behavior on initialization, you can re-initialize states after the fact:

# Re-initialize in FactoryGirl
FactoryGirl.define do
  factory :vehicle do
    after_build {|user| user.send(:initialize_state_machines, :dynamic => :force)}
  end
end

# Alternatively re-initialize in your model
class Vehicle < ActiveRecord::Base
  ...
  before_validation :on => :create {|user| user.send(:initialize_state_machines, :dynamic => :force)}
end

Dependencies

Ruby versions officially supported and tested:

Ruby (MRI) 1.8.6+
JRuby (1.8, 1.9)
Rubinius (1.8, 1.9)

ORM versions officially supported and tested:

ActiveModel integration: 3.0.0 or later
ActiveRecord integration: 2.0.0 or later
DataMapper integration: 0.9.4 or later
Mongoid integration: 2.0.0 or later
MongoMapper integration: 0.5.5 or later
Sequel integration: 2.8.0 or later

If graphing state machine:

ruby-graphviz: 0.9.17 or later