Adds support for integrating state machines with ActiveRecord models.
Below is an example of a simple state machine defined within an ActiveRecord model:
class Vehicle < ActiveRecord::Base 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, the action that will be invoked when a state is transitioned is the save action. This will cause the record to save the changes made to the state machine's attribute. Note that if any other changes were made to the record prior to transition, then those changes will be saved as well.
For example,
vehicle = Vehicle.create # => #<Vehicle id: 1, name: nil, state: "parked"> vehicle.name = 'Ford Explorer' vehicle.ignite # => true vehicle.reload # => #<Vehicle id: 1, name: "Ford Explorer", state: "idling">
As described in StateMachine::InstanceMethods#state_machine, event attributes are created for every machine that allow transitions to be performed automatically when the object's action (in this case, :save) is called.
In ActiveRecord, these automated events are run in the following order:
before validation - Run before callbacks and persist new states, then validate
before save - If validation was skipped, run before callbacks and persist new states, then save
after save - Run after callbacks
For example,
vehicle = Vehicle.create # => #<Vehicle id: 1, name: nil, state: "parked"> vehicle.state_event # => nil vehicle.state_event = 'invalid' vehicle.valid? # => false vehicle.errors.full_messages # => ["State event is invalid"] vehicle.state_event = 'ignite' vehicle.valid? # => true vehicle.save # => true vehicle.state # => "idling" vehicle.state_event # => nil
Note that this can also be done on a mass-assignment basis:
vehicle = Vehicle.create(:state_event => 'ignite') # => #<Vehicle id: 1, name: nil, state: "idling"> vehicle.state # => "idling"
This technique is always used for transitioning states when the save action (which is the default) is configured for the machine.
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 < ActiveRecord::Base 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 < ActiveRecord::Base 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
In order to ensure that any changes made during transition callbacks are rolled back during a failed attempt, every transition is wrapped within a transaction.
For example,
class Message < ActiveRecord::Base end Vehicle.state_machine do before_transition do |vehicle, transition| Message.create(:content => transition.inspect) false end end vehicle = Vehicle.create # => #<Vehicle id: 1, name: nil, state: "parked"> vehicle.ignite # => false Message.count # => 0
Note that only before callbacks that halt the callback chain and failed attempts to save the record will result in the transaction being rolled back. If an after callback halts the chain, the previous result still applies and the transaction is not rolled back.
To turn off transactions:
class Vehicle < ActiveRecord::Base state_machine :initial => :parked, :use_transactions => false do ... end end
If using the save action for the machine, this option will be ignored as the transaction will be created by ActiveRecord within save.
If an event fails to successfully fire because there are no matching transitions for the current record, a validation error is added to the record's state attribute to help in determining why it failed and for reporting via the UI.
For example,
vehicle = Vehicle.create(:state => 'idling') # => #<Vehicle id: 1, name: nil, state: "idling"> vehicle.ignite # => false vehicle.errors.full_messages # => ["State cannot transition via \"ignite\""]
If an event fails to fire because of a validation error on the record and not because a matching transition was not available, no error messages will be added to the state attribute.
To assist in filtering models with specific states, a series of named scopes are defined on the model for finding records with or without a particular set of states.
These named scopes are essentially the functional equivalent of the following definitions:
class Vehicle < ActiveRecord::Base named_scope :with_states, lambda {|*states| {:conditions => {:state => states}}} # with_states also aliased to with_state named_scope :without_states, lambda {|*states| {:conditions => ['state NOT IN (?)', states]}} # without_states also aliased to without_state end
Note, however, that the states are converted to their stored values before being passed into the query.
Because of the way named scopes work in ActiveRecord, they can be chained like so:
Vehicle.with_state(:parked).all(:order => 'id DESC')
All before/after transition callbacks defined for ActiveRecord models behave in the same way that other ActiveRecord callbacks behave. The object involved in the transition is passed in as an argument.
For example,
class Vehicle < ActiveRecord::Base 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 addition to support for ActiveRecord-like hooks, there is additional support for ActiveRecord observers. Because of the way ActiveRecord 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 record'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 < ActiveRecord::Observer def before_save(vehicle) # log message end # 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 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 < ActiveRecord::Observer observe Vehicle, Switch, Project def after_transition(record, transition) Audit.log(record, transition) end end
In Rails 2.2+, any error message that is generated from performing invalid transitions can be localized. The following default translations are used:
en: activerecord: errors: messages: invalid: "is invalid" invalid_event: "cannot transition when %{state}" invalid_transition: "cannot transition via %{event}"
Notice that the interpolation syntax is %{key} in Rails 3+. In Rails 2.x, the appropriate syntax is {{key}}.
You can override these for a specific model like so:
en: activerecord: 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:
activerecord.state_machines.vehicle.state.states.parked
<tt>activerecord.state_machines.state.states.parked
activerecord.state_machines.states.parked
Event translations will be looked for using the following keys:
activerecord.state_machines.vehicle.state.events.ignite
<tt>activerecord.state_machines.state.events.ignite
activerecord.state_machines.events.ignite
An example translation configuration might look like so:
es: activerecord: state_machines: states: parked: 'estacionado' events: park: 'estacionarse'
# File lib/state_machine/integrations/active_record/versions.rb, line 5 def self.active? ::ActiveRecord::VERSION::MAJOR == 2 end
Whether this integration is available. Only true if ActiveRecord::Base is defined.
# File lib/state_machine/integrations/active_record.rb, line 328 def self.available? defined?(::ActiveRecord::Base) end
Should this integration be used for state machines in the given class? Classes that inherit from ActiveRecord::Base will automatically use the ActiveRecord integration.
# File lib/state_machine/integrations/active_record.rb, line 335 def self.matches?(klass) klass <= ::ActiveRecord::Base end
# File lib/state_machine/integrations/active_record/versions.rb, line 68 def action_hook action == :save ? :create_or_update : super end
# File lib/state_machine/integrations/active_record/versions.rb, line 95 def ancestors_for(klass) klass.self_and_descendents_from_active_record end
# File lib/state_machine/integrations/active_record/versions.rb, line 85 def default_error_message_options(object, attribute, message) {:default => @messages[message]} end
# File lib/state_machine/integrations/active_record/versions.rb, line 64 def i18n_scope(klass) :activerecord end
# File lib/state_machine/integrations/active_record/versions.rb, line 36 def invalidate(object, attribute, message, values = []) if defined?(I18n) super else object.errors.add(self.attribute(attribute), generate_message(message, values)) end end
# File lib/state_machine/integrations/active_record/versions.rb, line 9 def load_locale super if defined?(I18n) end
# File lib/state_machine/integrations/active_record/versions.rb, line 72 def load_observer_extensions super ::ActiveRecord::Observer.class_eval do include StateMachine::Integrations::ActiveModel::Observer end unless ::ActiveRecord::Observer < StateMachine::Integrations::ActiveModel::Observer end
# File lib/state_machine/integrations/active_record/versions.rb, line 105 def supports_dirty_tracking?(object) false end
# File lib/state_machine/integrations/active_record/versions.rb, line 60 def supports_mass_assignment_security? true end
# File lib/state_machine/integrations/active_record/versions.rb, line 52 def supports_observers? true end
Runs state events around the machine's :save action
# File lib/state_machine/integrations/active_record.rb, line 382 def around_save(object) object.class.state_machines.transitions(object, action).perform { yield } end
Generates the fully-qualifed column name for this machine's attribute
# File lib/state_machine/integrations/active_record.rb, line 399 def attribute_column connection = owner_class.connection "#{connection.quote_table_name(owner_class.table_name)}.#{connection.quote_column_name(attribute)}" end
Defines a new named scope with the given name
# File lib/state_machine/integrations/active_record.rb, line 412 def create_scope(name, scope) lambda {|model, values| model.where(scope.call(values))} end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/active_record.rb, line 388 def create_with_scope(name) create_scope(name, lambda {|values| ["#{attribute_column} IN (?)", values]}) end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/active_record.rb, line 394 def create_without_scope(name) create_scope(name, lambda {|values| ["#{attribute_column} NOT IN (?)", values]}) end
Uses around callbacks to run state events if using the :save hook
# File lib/state_machine/integrations/active_record.rb, line 373 def define_action_hook if action_hook == :save owner_class.set_callback(:save, :around, self, :prepend => true) else super end end
Defines an initialization hook into the owner class for setting the initial state of the machine before any attributes are set on the object
# File lib/state_machine/integrations/active_record.rb, line 353 def define_state_initializer define_helper :instance, # Initializes dynamic states def initialize(*) super do |*args| self.class.state_machines.initialize_states(self, :static => false) yield(*args) if block_given? end end # Initializes static states def attributes_from_column_definition(*) result = super self.class.state_machines.initialize_states(self, :dynamic => false, :to => result) result end, __FILE__, __LINE__ + 1 end
ActiveModel's use of method_missing / respond_to for attribute methods breaks both ancestor lookups and defined?(super). Need to special-case the existence of query attribute methods.
# File lib/state_machine/integrations/active_record.rb, line 419 def owner_class_ancestor_has_method?(method) method == "#{name}?" || super end
Only runs validations on the action if using :save
# File lib/state_machine/integrations/active_record.rb, line 346 def runs_validations_on_action? action == :save end
Runs a new database transaction, rolling back any changes by raising an ActiveRecord::Rollback exception if the yielded block fails (i.e. returns false).
# File lib/state_machine/integrations/active_record.rb, line 407 def transaction(object) object.class.transaction {raise ::ActiveRecord::Rollback unless yield} end
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