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:
-
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.
Public Class Methods
# File lib/state_machine/integrations/active_model/versions.rb 5 def self.active? 6 !defined?(::ActiveModel::VERSION) || ::ActiveModel::VERSION::MAJOR == 2 7 end
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
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
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
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
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
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 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
# 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
Configures new event with the built-in humanize scheme
# 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
Configures new states with the built-in humanize scheme
# 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
Initializes class-level extensions and defaults for this machine
# 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
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
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
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
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
Adds hooks into validation for automatically firing events
# 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
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
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
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
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
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
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
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
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
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
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