Module StateMachine::Integrations::ActiveModel
In: lib/state_machine/integrations/active_model/versions.rb
lib/state_machine/integrations/active_model/observer.rb
lib/state_machine/integrations/active_model.rb

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:

  • ActiveModel::Observing
  • ActiveModel::Validations

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:

  • before/after/after_failure_to-_ignite_from_parked_to_idling
  • before/after/after_failure_to-_ignite_from_parked
  • before/after/after_failure_to-_ignite_to_idling
  • before/after/after_failure_to-_ignite
  • before/after/after_failure_to-_transition_state_from_parked_to_idling
  • before/after/after_failure_to-_transition_state_from_parked
  • before/after/after_failure_to-_transition_state_to_idling
  • before/after/after_failure_to-_transition_state
  • before/after/after_failure_to-_transition

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":

  • activemodel.state_machines.#{model_name}.#{machine_name}.states.#{state_name}
  • activemodel.state_machines.#{model_name}.states.#{state_name}
  • activemodel.state_machines.#{machine_name}.states.#{state_name}
  • activemodel.state_machines.states.#{state_name}

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

  • activemodel.state_machines.#{model_name}.#{machine_name}.events.#{event_name}
  • activemodel.state_machines.#{model_name}.events.#{event_name}
  • activemodel.state_machines.#{machine_name}.events.#{event_name}
  • activemodel.state_machines.events.#{event_name}

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.

Methods

Included Modules

Base

Classes and Modules

Module StateMachine::Integrations::ActiveModel::Observer

Public Class methods

[Source]

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

[Source]

    # File lib/state_machine/integrations/active_model/versions.rb, line 20
20:         def self.active?
21:           defined?(::ActiveModel::VERSION) && ::ActiveModel::VERSION::MAJOR == 3 && ::ActiveModel::VERSION::MINOR == 0
22:         end

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 371
371:       def self.available?
372:         defined?(::ActiveModel)
373:       end

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.

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 378
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

[Source]

    # File lib/state_machine/integrations/active_model/versions.rb, line 9
 9:         def define_validation_hook
10:           define_helper :instance, "def valid?(*)\nself.class.state_machines.transitions(self, \#{action.inspect}, :after => false).perform { super }\nend\n", __FILE__, __LINE__ + 1
11:         end

[Source]

    # File lib/state_machine/integrations/active_model/versions.rb, line 24
24:         def define_validation_hook
25:           # +around+ callbacks don't have direct access to results until AS 3.1
26:           owner_class.set_callback(:validation, :after, 'value', :prepend => true)
27:           super
28:         end

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 398
398:       def errors_for(object)
399:         object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', '
400:       end

Adds a validation error to the given object

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 383
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

Resets any errors previously added when invalidating the given object

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 403
403:       def reset(object)
404:         object.errors.clear if supports_validations?
405:       end

Protected Instance methods

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 526
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

Adds a set of default callbacks that utilize the Observer extensions

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 488
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

Configures new event with the built-in humanize scheme

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 546
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

Configures new states with the built-in humanize scheme

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 539
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

Initializes class-level extensions and defaults for this machine

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 470
470:         def after_initialize
471:           super
472:           load_locale
473:           load_observer_extensions
474:           add_default_callbacks
475:         end

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 465
465:         def ancestors_for(klass)
466:           klass.lookup_ancestors
467:         end

Runs state events around the object‘s validation process

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 519
519:         def around_validation(object)
520:           object.class.state_machines.transitions(object, action, :after => false).perform { yield }
521:         end

Gets the terminator to use for callbacks

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 428
428:         def callback_terminator
429:           @terminator ||= lambda {|result| result == false}
430:         end

The default options to use when generating messages for validation errors

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 439
439:         def default_error_message_options(object, attribute, message)
440:           {:message => @messages[message]}
441:         end

Adds hooks into validation for automatically firing events

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 507
507:         def define_action_helpers
508:           super
509:           define_validation_hook if runs_validations_on_action?
510:         end

Skips defining reader/writer methods since this is done automatically

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 497
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

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 514
514:         def define_validation_hook
515:           owner_class.set_callback(:validation, :around, self, :prepend => true)
516:         end

Determines the base scope to use when looking up translations

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 433
433:         def i18n_scope(klass)
434:           klass.i18n_scope
435:         end

Loads any locale files needed for translating validation errors

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 478
478:         def load_locale
479:           I18n.load_path.unshift(@integration.locale_path) unless I18n.load_path.include?(@integration.locale_path)
480:         end

Loads extensions to ActiveModel‘s Observers

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 483
483:         def load_observer_extensions
484:           require 'state_machine/integrations/active_model/observer'
485:         end

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.

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 567
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

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.

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 423
423:         def runs_validations_on_action?
424:           false
425:         end

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 410
410:         def supports_observers?
411:           defined?(::ActiveModel::Observing) && owner_class <= ::ActiveModel::Observing
412:         end

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

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 416
416:         def supports_validations?
417:           defined?(::ActiveModel::Validations) && owner_class <= ::ActiveModel::Validations
418:         end

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.

[Source]

     # File lib/state_machine/integrations/active_model.rb, line 451
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}""#{ancestor.model_name.underscore}.#{name}.#{group}.#{value}"}
458:           translations.concat(ancestors.map {|ancestor| "#{ancestor.model_name.underscore}.#{group}.#{value}""#{ancestor.model_name.underscore}.#{group}.#{value}"})
459:           translations.concat(["#{name}.#{group}.#{value}""#{name}.#{group}.#{value}", "#{group}.#{value}""#{group}.#{value}", value.humanize.downcase])
460:           I18n.translate(translations.shift, :default => translations, :scope => [i18n_scope(klass), :state_machines])
461:         end

[Validate]