module StateMachines::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::Validations
Below is an example of a simple state machine defined within an ActiveModel
class:
class Vehicle 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 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.current 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 ActiveModel mattr_accessor(: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.
Constants
- VERSION
Public Class Methods
Classes that include ActiveModel::Validations will automatically use the ActiveModel
integration.
# File lib/state_machines/integrations/active_model.rb, line 369 def self.matching_ancestors [::ActiveModel, ::ActiveModel::Validations] end
Public Instance Methods
Runs state events around the object's validation process
# File lib/state_machines/integrations/active_model.rb, line 399 def around_validation(object) object.class.state_machines.transitions(object, action, after: false).perform { yield } end
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_machines/integrations/active_model.rb, line 389 def errors_for(object) object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', ' end
Adds a validation error to the given object
# File lib/state_machines/integrations/active_model.rb, line 374 def invalidate(object, attribute, message, values = []) if supports_validations? attribute = self.attribute(attribute) options = values.reduce({}) do |h, (key, value)| h[key] = value h end default_options = default_error_message_options(object, attribute, message) object.errors.add(attribute, message, **options, **default_options) end end
Resets any errors previously added when invalidating the given object
# File lib/state_machines/integrations/active_model.rb, line 394 def reset(object) object.errors.clear if supports_validations? 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_machines/integrations/active_model.rb, line 493 def add_callback(type, options, &block) options[:terminator] = callback_terminator super end
Configures new event with the built-in humanize scheme
# File lib/state_machines/integrations/active_model.rb, line 506 def add_events(*) super.each do |new_event| new_event.human_name = ->(event, klass) { translate(klass, :event, event.name) } end end
Configures new states with the built-in humanize scheme
# File lib/state_machines/integrations/active_model.rb, line 499 def add_states(*) super.each do |new_state| new_state.human_name = ->(state, klass) { translate(klass, :state, state.name) } end 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_machines/integrations/active_model.rb, line 464 def ancestors_for(klass) klass.lookup_ancestors end
Gets the terminator to use for callbacks
# File lib/state_machines/integrations/active_model.rb, line 427 def callback_terminator @terminator ||= ->(result) { result == false } end
The default options to use when generating messages for validation errors
# File lib/state_machines/integrations/active_model.rb, line 438 def default_error_message_options(_object, _attribute, message) { message: @messages[message] } end
Adds hooks into validation for automatically firing events
# File lib/state_machines/integrations/active_model.rb, line 479 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_machines/integrations/active_model.rb, line 469 def define_state_accessor name = self.name owner_class.validates_each(attribute) do |object| machine = object.class.state_machine(name) machine.invalidate(object, :state, :invalid) unless machine.states.match(object) end if supports_validations? end
# File lib/state_machines/integrations/active_model.rb, line 405 def define_state_initializer define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 def initialize(params = {}) self.class.state_machines.initialize_states(self, {}, params) { super } end end_eval end
Hooks into validations by defining around callbacks for the :validation event
# File lib/state_machines/integrations/active_model.rb, line 486 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_machines/integrations/active_model.rb, line 432 def i18n_scope(klass) klass.i18n_scope 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_machines/integrations/active_model.rb, line 422 def runs_validations_on_action? false end
Whether validations are supported in the integration. Only true if the ActiveModel
feature is enabled on the owner class.
# File lib/state_machines/integrations/active_model.rb, line 415 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.#{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_machines/integrations/active_model.rb, line 450 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.to_s.underscore}.#{name}.#{group}.#{value}" } translations.concat(ancestors.map { |ancestor| :"#{ancestor.model_name.to_s.underscore}.#{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