Adds support for integrating state machines with ActiveModel classes.
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::Dirty
ActiveModel::Observing
ActiveModel::Validations
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.
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
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\""]
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
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.
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
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"]
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:
i18n scope (locale)
Machine defaults
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.
# File lib/state_machine/integrations/active_model/versions.rb, line 5 def self.active? !defined?(::ActiveModel::VERSION) || ::ActiveModel::VERSION::MAJOR == 2 end
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Hooks into validations by defining around callbacks for the :validation event
# File lib/state_machine/integrations/active_model.rb, line 425 def define_validation_hook owner_class.set_callback(:validation, :around, self, :prepend => true) end
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
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
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
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
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
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
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
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
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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