StateMachine::Integrations::ActiveModel

Adds support for integrating state machines with ActiveModel classes.

Examples

If using ActiveModel directly within your class, then any one of the following features need to be included in order for the integration to be detected:

Below is an example of a simple state machine defined within an ActiveModel class:

class Vehicle
  include ActiveModel::Dirty
  include ActiveModel::Observing
  include ActiveModel::Validations

  attr_accessor :state
  define_attribute_methods [:state]

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

The examples in the sections below will use the above class as a reference.

Actions

By default, no action will be invoked when a state is transitioned. This means that if you want to save changes when transitioning, you must define the action yourself like so:

class Vehicle
  include ActiveModel::Validations
  attr_accessor :state

  state_machine :action => :save do
    ...
  end

  def save
    # Save changes
  end
end

Validation errors

In order to hook in validation support for your model, the ActiveModel::Validations feature must be included. If this is included and an event fails to successfully fire because there are no matching transitions for the object, a validation error is added to the object's state attribute to help in determining why it failed.

For example,

vehicle = Vehicle.new
vehicle.ignite                # => false
vehicle.errors.full_messages  # => ["State cannot transition via \"ignite\""]

Security implications

Beware that public event attributes mean that events can be fired whenever mass-assignment is being used. If you want to prevent malicious users from tampering with events through URLs / forms, the attribute should be protected like so:

class Vehicle
  include ActiveModel::MassAssignmentSecurity
  attr_accessor :state

  attr_protected :state_event
  # attr_accessible ... # Alternative technique

  state_machine do
    ...
  end
end

If you want to only have some events be able to fire via mass-assignment, you can build two state machines (one public and one protected) like so:

class Vehicle
  include ActiveModel::MassAssignmentSecurity
  attr_accessor :state

  attr_protected :state_event # Prevent access to events in the first machine

  state_machine do
    # Define private events here
  end

  # Public machine targets the same state as the private machine
  state_machine :public_state, :attribute => :state do
    # Define public events here
  end
end

Callbacks

All before/after transition callbacks defined for ActiveModel models behave in the same way that other ActiveSupport callbacks behave. The object involved in the transition is passed in as an argument.

For example,

class Vehicle
  include ActiveModel::Validations
  attr_accessor :state

  state_machine :initial => :parked do
    before_transition any => :idling do |vehicle|
      vehicle.put_on_seatbelt
    end

    before_transition do |vehicle, transition|
      # log message
    end

    event :ignite do
      transition :parked => :idling
    end
  end

  def put_on_seatbelt
    ...
  end
end

Note, also, that the transition can be accessed by simply defining additional arguments in the callback block.

Observers

In order to hook in observer support for your application, the ActiveModel::Observing feature must be included. Because of the way ActiveModel observers are designed, there is less flexibility around the specific transitions that can be hooked in. However, a large number of hooks are supported. For example, if a transition for a object's state attribute changes the state from parked to idling via the ignite event, the following observer methods are supported:

The following class shows an example of some of these hooks:

class VehicleObserver < ActiveModel::Observer
  # Callback for :ignite event *before* the transition is performed
  def before_ignite(vehicle, transition)
    # log message
  end

  # Callback for :ignite event *after* the transition has been performed
  def after_ignite(vehicle, transition)
    # put on seatbelt
  end

  # Generic transition callback *before* the transition is performed
  def after_transition(vehicle, transition)
    Audit.log(vehicle, transition)
  end

  def after_failure_to_transition(vehicle, transition)
    Audit.error(vehicle, transition)
  end
end

More flexible transition callbacks can be defined directly within the model as described in StateMachine::Machine#before_transition and StateMachine::Machine#after_transition.

To define a single observer for multiple state machines:

class StateMachineObserver < ActiveModel::Observer
  observe Vehicle, Switch, Project

  def after_transition(object, transition)
    Audit.log(object, transition)
  end
end

Dirty Attribute Tracking

In order to hook in validation support for your model, the ActiveModel::Validations feature must be included. If this is included then state attributes will always be properly marked as changed whether they were a callback or not.

For example,

class Vehicle
  include ActiveModel::Dirty
  attr_accessor :state

  state_machine :initial => :parked do
    event :park do
      transition :parked => :parked
    end
  end
end

vehicle = Vehicle.new
vehicle.changed         # => []
vehicle.park            # => true
vehicle.changed         # => ["state"]

Creating new integrations

If you want to integrate state_machine with an ORM that implements parts or all of the ActiveModel API, the following features must be specified:

For example,

module StateMachine::Integrations::MyORM
  include StateMachine::Integrations::ActiveModel

  @defaults = {:action = > :persist}

  def self.matches?(klass)
    defined?(::MyORM::Base) && klass <= ::MyORM::Base
  end

  def self.extended(base)
    locale = "#{File.dirname(__FILE__)}/my_orm/locale.rb"
    I18n.load_path << locale unless I18n.load_path.include?(locale)
  end

  protected
    def runs_validations_on_action?
      action == :persist
    end

    def i18n_scope
      :myorm
    end
end

If you wish to implement other features, such as attribute initialization with protected attributes, named scopes, or database transactions, you must add these independent of the ActiveModel integration. See the ActiveRecord implementation for examples of these customizations.

Public Class Methods

active?() click to toggle source
# File lib/state_machine/integrations/active_model/versions.rb, line 5
def self.active?
  !defined?(::ActiveModel::VERSION) || ::ActiveModel::VERSION::MAJOR == 2
end
available?() click to toggle source

Whether this integration is available. Only true if ActiveModel is defined.

# File lib/state_machine/integrations/active_model.rb, line 272
def self.available?
  defined?(::ActiveModel)
end
matches?(klass) click to toggle source

Should this integration be used for state machines in the given class? Classes that include ActiveModel::Dirty, ActiveModel::Observing, or ActiveModel::Validations will automatically use the ActiveModel integration.

# File lib/state_machine/integrations/active_model.rb, line 280
def self.matches?(klass)
  %(Dirty Observing Validations).any? {|feature| ::ActiveModel.const_defined?(feature) && klass <= ::ActiveModel.const_get(feature)}
end

Public Instance Methods

define_validation_hook() click to toggle source
# File lib/state_machine/integrations/active_model/versions.rb, line 9
def define_validation_hook
  define_helper :instance,             def valid?(*)              self.class.state_machines.transitions(self, #{action.inspect}, :after => false).perform { super }            end, __FILE__, __LINE__ + 1
end
invalidate(object, attribute, message, values = []) click to toggle source

Adds a validation error to the given object

# File lib/state_machine/integrations/active_model.rb, line 297
def invalidate(object, attribute, message, values = [])
  if supports_validations?
    attribute = self.attribute(attribute)
    options = values.inject({}) do |options, (key, value)|
      options[key] = value
      options
    end
    
    default_options = default_error_message_options(object, attribute, message)
    object.errors.add(attribute, message, options.merge(default_options))
  end
end
reset(object) click to toggle source

Resets any errors previously added when invalidating the given object

# File lib/state_machine/integrations/active_model.rb, line 311
def reset(object)
  object.errors.clear if supports_validations?
end
write(object, attribute, value, *args) click to toggle source

Forces the change in state to be recognized regardless of whether the state value actually changed

# File lib/state_machine/integrations/active_model.rb, line 286
def write(object, attribute, value, *args)
  result = super
  
  if (attribute == :state || attribute == :event && value) && supports_dirty_tracking?(object) && !object.send("#{self.attribute}_changed?")
    object.send("#{self.attribute}_will_change!")
  end
  
  result
end

Protected Instance Methods

add_callback(type, options, &block) click to toggle source

Creates a new callback in the callback chain, always inserting it before the default Observer callbacks that were created after initialization.

# File lib/state_machine/integrations/active_model.rb, line 437
def add_callback(type, options, &block)
  options[:terminator] = callback_terminator
  
  if supports_observers?
    @callbacks[type == :around ? :before : type].insert(-2, callback = Callback.new(type, options, &block))
    add_states(callback.known_states)
    callback
  else
    super
  end
end
add_default_callbacks() click to toggle source

Adds a set of default callbacks that utilize the Observer extensions

# File lib/state_machine/integrations/active_model.rb, line 399
def add_default_callbacks
  if supports_observers?
    callbacks[:before] << Callback.new(:before) {|object, transition| notify(:before, object, transition)}
    callbacks[:after] << Callback.new(:after) {|object, transition| notify(:after, object, transition)}
    callbacks[:failure] << Callback.new(:failure) {|object, transition| notify(:after_failure_to, object, transition)}
  end
end
add_events(new_events) click to toggle source

Configures new event with the built-in humanize scheme

# File lib/state_machine/integrations/active_model.rb, line 457
def add_events(new_events)
  super.each do |event|
    event.human_name = lambda {|event, klass| translate(klass, :event, event.name)}
  end
end
add_states(new_states) click to toggle source

Configures new states with the built-in humanize scheme

# File lib/state_machine/integrations/active_model.rb, line 450
def add_states(new_states)
  super.each do |state|
    state.human_name = lambda {|state, klass| translate(klass, :state, state.name)}
  end
end
after_initialize() click to toggle source

Initializes class-level extensions and defaults for this machine

# File lib/state_machine/integrations/active_model.rb, line 382
def after_initialize
  load_locale
  load_observer_extensions
  add_default_callbacks
end
ancestors_for(klass) click to toggle source

Build a list of ancestors for the given class to use when determining which localization key to use for a particular string.

# File lib/state_machine/integrations/active_model.rb, line 377
def ancestors_for(klass)
  klass.lookup_ancestors
end
around_validation(object) click to toggle source

Runs state events around the object's validation process

# File lib/state_machine/integrations/active_model.rb, line 430
def around_validation(object)
  object.class.state_machines.transitions(object, action, :after => false).perform { yield }
end
callback_terminator() click to toggle source

Gets the terminator to use for callbacks

# File lib/state_machine/integrations/active_model.rb, line 342
def callback_terminator
  @terminator ||= lambda {|result| result == false}
end
default_error_message_options(object, attribute, message) click to toggle source

The default options to use when generating messages for validation errors

# File lib/state_machine/integrations/active_model.rb, line 353
def default_error_message_options(object, attribute, message)
  {:message => @messages[message]}
end
define_action_helpers() click to toggle source

Adds hooks into validation for automatically firing events

# File lib/state_machine/integrations/active_model.rb, line 418
def define_action_helpers
  super
  define_validation_hook if runs_validations_on_action?
end
define_state_accessor() click to toggle source

Skips defining reader/writer methods since this is done automatically

# File lib/state_machine/integrations/active_model.rb, line 408
def define_state_accessor
  name = self.name
  
  owner_class.validates_each(attribute) do |object, attr, value|
    machine = object.class.state_machine(name)
    machine.invalidate(object, :state, :invalid) unless machine.states.match(object)
  end if supports_validations?
end
i18n_scope(klass) click to toggle source

Determines the base scope to use when looking up translations

# File lib/state_machine/integrations/active_model.rb, line 347
def i18n_scope(klass)
  klass.i18n_scope
end
load_locale() click to toggle source

Loads any locale files needed for translating validation errors

# File lib/state_machine/integrations/active_model.rb, line 389
def load_locale
  I18n.load_path.unshift(@integration.locale_path) unless I18n.load_path.include?(@integration.locale_path)
end
load_observer_extensions() click to toggle source

Loads extensions to ActiveModel's Observers

# File lib/state_machine/integrations/active_model.rb, line 394
def load_observer_extensions
  require 'state_machine/integrations/active_model/observer'
end
notify(type, object, transition) click to toggle source

Notifies observers on the given object that a callback occurred involving the given transition. This will attempt to call the following methods on observers:

  • #{type}_#{qualified_event}from#{from}to#{to}

  • #{type}_#{qualified_event}from#{from}

  • #{type}_#{qualified_event}to#{to}

  • #{type}_#{qualified_event}

  • #{type}transition#{machine_name}from#{from}to#{to}

  • #{type}transition#{machine_name}from#{from}

  • #{type}transition#{machine_name}to#{to}

  • #{type}transition#{machine_name}

  • #{type}_transition

This will always return true regardless of the results of the callbacks.

# File lib/state_machine/integrations/active_model.rb, line 478
def notify(type, object, transition)
  name = self.name
  event = transition.qualified_event
  from = transition.from_name
  to = transition.to_name
  
  # Machine-specific updates
  ["#{type}_#{event}", "#{type}_transition_#{name}"].each do |event_segment|
    ["_from_#{from}", nil].each do |from_segment|
      ["_to_#{to}", nil].each do |to_segment|
        object.class.changed if object.class.respond_to?(:changed)
        object.class.notify_observers([event_segment, from_segment, to_segment].join, object, transition)
      end
    end
  end
  
  # Generic updates
  object.class.changed if object.class.respond_to?(:changed)
  object.class.notify_observers("#{type}_transition", object, transition)
  
  true
end
runs_validations_on_action?() click to toggle source

Do validations run when the action configured this machine is invoked? This is used to determine whether to fire off attribute-based event transitions when the action is run.

# File lib/state_machine/integrations/active_model.rb, line 331
def runs_validations_on_action?
  false
end
supports_dirty_tracking?(object) click to toggle source

Whether change (dirty) tracking is supported in the integration. Only true if the ActiveModel feature is enabled on the owner class.

# File lib/state_machine/integrations/active_model.rb, line 337
def supports_dirty_tracking?(object)
  defined?(::ActiveModel::Dirty) && owner_class <= ::ActiveModel::Dirty && object.respond_to?("#{self.attribute}_changed?")
end
supports_observers?() click to toggle source

Whether observers are supported in the integration. Only true if ActiveModel::Observer is available.

# File lib/state_machine/integrations/active_model.rb, line 318
def supports_observers?
  defined?(::ActiveModel::Observing) && owner_class <= ::ActiveModel::Observing
end
supports_validations?() click to toggle source

Whether validations are supported in the integration. Only true if the ActiveModel feature is enabled on the owner class.

# File lib/state_machine/integrations/active_model.rb, line 324
def supports_validations?
  defined?(::ActiveModel::Validations) && owner_class <= ::ActiveModel::Validations
end
translate(klass, key, value) click to toggle source

Translates the given key / value combo. Translation keys are looked up in the following order:

  • #{i18n_scope}.state_machines.#{model_name}.#{machine_name}.#{plural_key}.#{value}

  • #{i18n_scope}.state_machines.#{machine_name}.#{plural_key}.#{value}

  • #{i18n_scope}.state_machines.#{plural_key}.#{value}

If no keys are found, then the humanized value will be the fallback.

# File lib/state_machine/integrations/active_model.rb, line 364
def translate(klass, key, value)
  ancestors = ancestors_for(klass)
  group = key.to_s.pluralize
  value = value ? value.to_s : 'nil'
  
  # Generate all possible translation keys
  translations = ancestors.map {|ancestor| :"#{ancestor.model_name.underscore}.#{name}.#{group}.#{value}"}
  translations.concat([:"#{name}.#{group}.#{value}", :"#{group}.#{value}", value.humanize.downcase])
  I18n.translate(translations.shift, :default => translations, :scope => [i18n_scope(klass), :state_machines])
end

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