Module | StateMachine::Integrations::ActiveModel |
In: |
lib/state_machine/integrations/active_model.rb
lib/state_machine/integrations/active_model/observer.rb lib/state_machine/integrations/active_model/versions.rb |
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:
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:
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:
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.
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.
Creates a new callback in the callback chain, always inserting it before the default Observer callbacks that were created after initialization.
Build a list of ancestors for the given class to use when determining which localization key to use for a particular string.
Notifies observers on the given object that a callback occurred involving the given transition. This will attempt to call the following methods on observers:
This will always return true regardless of the results of the callbacks.
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.
Whether change (dirty) tracking is supported in the integration. Only true if the ActiveModel feature is enabled on the owner class.
Whether observers are supported in the integration. Only true if ActiveModel::Observer is available.
Whether validations are supported in the integration. Only true if the ActiveModel feature is enabled on the owner class.
Translates the given key / value combo. Translation keys are looked up in the following order:
If no keys are found, then the humanized value will be the fallback.