module 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::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

Validations

As mentioned in StateMachine::Machine#state, you can define behaviors, like validations, that only execute for certain states. One important caveat here is that, due to a constraint in ActiveModel's validation framework, custom validators will not work as expected when defined to run in multiple states. For example:

class Vehicle
  include ActiveModel::Validations

  state_machine do
    ...
    state :first_gear, :second_gear do
      validate :speed_is_legal
    end
  end
end

In this case, the :speed_is_legal validation will only get run for the :second_gear state. To avoid this, you can define your custom validation like so:

class Vehicle
  include ActiveModel::Validations

  state_machine do
    ...
    state :first_gear, :second_gear do
      validate {|vehicle| vehicle.speed_is_legal}
    end
  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\""]

In addition, if you're using the ignite! version of the event, then the failure reason (such as the current validation errors) will be included in the exception that gets raised when the event fails. For example, assuming there's a validation on a field called name on the class:

vehicle = Vehicle.new
vehicle.ignite!       # => StateMachine::InvalidTransition: Cannot transition state via :ignite from :parked (Reason(s): Name cannot be blank)

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

Internationalization

Any error message that is generated from performing invalid transitions can be localized. The following default translations are used:

en:
  activemodel:
    errors:
      messages:
        invalid: "is invalid"
        # %{value} = attribute value, %{state} = Human state name
        invalid_event: "cannot transition when %{state}"
        # %{value} = attribute value, %{event} = Human event name, %{state} = Human current state name
        invalid_transition: "cannot transition via %{event}"

You can override these for a specific model like so:

en:
  activemodel:
    errors:
      models:
        user:
          invalid: "is not valid"

In addition to the above, you can also provide translations for the various states / events in each state machine. Using the Vehicle example, state translations will be looked for using the following keys, where model_name = “vehicle”, machine_name = “state” and state_name = “parked”:

Event translations will be looked for using the following keys, where model_name = “vehicle”, machine_name = “state” and event_name = “ignite”:

An example translation configuration might look like so:

es:
  activemodel:
    state_machines:
      states:
        parked: 'estacionado'
      events:
        park: 'estacionarse'

Dirty Attribute Tracking

When using the ActiveModel::Dirty extension, your model will keep track of any changes that are made to attributes. Depending on your ORM, an object will only be saved when there are attributes that have changed on the object. When integrating with state_machine, typically the state field will be marked as dirty after a transition occurs. In some situations, however, this isn't the case.

If you define loopback transitions in your state machine, the value for the machine's attribute (e.g. state) will not change. Unless you explicitly indicate so, this means that your object won't persist anything on a loopback. For example:

class Vehicle
  include ActiveModel::Validations
  include ActiveModel::Dirty
  attr_accessor :state

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

If, instead, you'd like your object to always persist regardless of whether the value actually changed, you can do so by using the #{attribute}_will_change! helpers or defining a before_transition callback that actually changes an attribute on the model. For example:

class Vehicle
  ...
  state_machine :initial => :parked do
    before_transition all => same do |vehicle|
      vehicle.state_will_change!

      # Alternative solution, updating timestamp
      # vehicle.updated_at = Time.curent
    end
  end
end

Creating new integrations

If you want to integrate state_machine with an ORM that implements parts or all of the ActiveModel API, only the machine defaults need to be specified. Otherwise, the implementation is similar to any other integration.

For example,

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

  @defaults = {:action = > :persist}

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

  protected
    def runs_validations_on_action?
      action == :persist
    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
5 def self.active?
6   !defined?(::ActiveModel::VERSION) || ::ActiveModel::VERSION::MAJOR == 2
7 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
371 def self.available?
372   defined?(::ActiveModel)
373 end
matches?(klass) click to toggle source

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

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

Public Instance Methods

errors_for(object) click to toggle source

Describes the current validation errors on the given object. If none are specific, then the default error is interpeted as a “halt”.

    # File lib/state_machine/integrations/active_model.rb
398 def errors_for(object)
399   object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', '
400 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
383 def invalidate(object, attribute, message, values = [])
384   if supports_validations?
385     attribute = self.attribute(attribute)
386     options = values.inject({}) do |options, (key, value)|
387       options[key] = value
388       options
389     end
390     
391     default_options = default_error_message_options(object, attribute, message)
392     object.errors.add(attribute, message, options.merge(default_options))
393   end
394 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
403 def reset(object)
404   object.errors.clear if supports_validations?
405 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.

Calls superclass method
    # File lib/state_machine/integrations/active_model.rb
526 def add_callback(type, options, &block)
527   options[:terminator] = callback_terminator
528   
529   if supports_observers?
530     @callbacks[type == :around ? :before : type].insert(-2, callback = Callback.new(type, options, &block))
531     add_states(callback.known_states)
532     callback
533   else
534     super
535   end
536 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
488 def add_default_callbacks
489   if supports_observers?
490     callbacks[:before] << Callback.new(:before) {|object, transition| notify(:before, object, transition)}
491     callbacks[:after] << Callback.new(:after) {|object, transition| notify(:after, object, transition)}
492     callbacks[:failure] << Callback.new(:failure) {|object, transition| notify(:after_failure_to, object, transition)}
493   end
494 end
add_events(new_events) click to toggle source

Configures new event with the built-in humanize scheme

Calls superclass method
    # File lib/state_machine/integrations/active_model.rb
546 def add_events(new_events)
547   super.each do |event|
548     event.human_name = lambda {|event, klass| translate(klass, :event, event.name)}
549   end
550 end
add_states(new_states) click to toggle source

Configures new states with the built-in humanize scheme

Calls superclass method
    # File lib/state_machine/integrations/active_model.rb
539 def add_states(new_states)
540   super.each do |state|
541     state.human_name = lambda {|state, klass| translate(klass, :state, state.name)}
542   end
543 end
after_initialize() click to toggle source

Initializes class-level extensions and defaults for this machine

Calls superclass method
    # File lib/state_machine/integrations/active_model.rb
470 def after_initialize
471   super
472   load_locale
473   load_observer_extensions
474   add_default_callbacks
475 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
465 def ancestors_for(klass)
466   klass.lookup_ancestors
467 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
519 def around_validation(object)
520   object.class.state_machines.transitions(object, action, :after => false).perform { yield }
521 end
callback_terminator() click to toggle source

Gets the terminator to use for callbacks

    # File lib/state_machine/integrations/active_model.rb
428 def callback_terminator
429   @terminator ||= lambda {|result| result == false}
430 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
439 def default_error_message_options(object, attribute, message)
440   {:message => @messages[message]}
441 end
define_action_helpers() click to toggle source

Adds hooks into validation for automatically firing events

Calls superclass method
    # File lib/state_machine/integrations/active_model.rb
507 def define_action_helpers
508   super
509   define_validation_hook if runs_validations_on_action?
510 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
497 def define_state_accessor
498   name = self.name
499   
500   owner_class.validates_each(attribute) do |object, attr, value|
501     machine = object.class.state_machine(name)
502     machine.invalidate(object, :state, :invalid) unless machine.states.match(object)
503   end if supports_validations?
504 end
define_validation_hook() click to toggle source

Hooks into validations by defining around callbacks for the :validation event

    # File lib/state_machine/integrations/active_model.rb
514 def define_validation_hook
515   owner_class.set_callback(:validation, :around, self, :prepend => true)
516 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
433 def i18n_scope(klass)
434   klass.i18n_scope
435 end
load_locale() click to toggle source

Loads any locale files needed for translating validation errors

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

Loads extensions to ActiveModel's Observers

    # File lib/state_machine/integrations/active_model.rb
483 def load_observer_extensions
484   require 'state_machine/integrations/active_model/observer'
485 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
567 def notify(type, object, transition)
568   name = self.name
569   event = transition.qualified_event
570   from = transition.from_name || 'nil'
571   to = transition.to_name || 'nil'
572   
573   # Machine-specific updates
574   ["#{type}_#{event}", "#{type}_transition_#{name}"].each do |event_segment|
575     ["_from_#{from}", nil].each do |from_segment|
576       ["_to_#{to}", nil].each do |to_segment|
577         object.class.changed if object.class.respond_to?(:changed)
578         object.class.notify_observers('update_with_transition', [[event_segment, from_segment, to_segment].join, object, transition])
579       end
580     end
581   end
582   
583   # Generic updates
584   object.class.changed if object.class.respond_to?(:changed)
585   object.class.notify_observers('update_with_transition', ["#{type}_transition", object, transition])
586   
587   true
588 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
423 def runs_validations_on_action?
424   false
425 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
410 def supports_observers?
411   defined?(::ActiveModel::Observing) && owner_class <= ::ActiveModel::Observing
412 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
416 def supports_validations?
417   defined?(::ActiveModel::Validations) && owner_class <= ::ActiveModel::Validations
418 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.#{model_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
451 def translate(klass, key, value)
452   ancestors = ancestors_for(klass)
453   group = key.to_s.pluralize
454   value = value ? value.to_s : 'nil'
455   
456   # Generate all possible translation keys
457   translations = ancestors.map {|ancestor| :"#{ancestor.model_name.underscore}.#{name}.#{group}.#{value}"}
458   translations.concat(ancestors.map {|ancestor| :"#{ancestor.model_name.underscore}.#{group}.#{value}"})
459   translations.concat([:"#{name}.#{group}.#{value}", :"#{group}.#{value}", value.humanize.downcase])
460   I18n.translate(translations.shift, :default => translations, :scope => [i18n_scope(klass), :state_machines])
461 end