module StateMachine::Integrations::ActiveRecord
Adds support for integrating state machines with ActiveRecord models.
Examples¶ ↑
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.
Actions¶ ↑
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">
Events¶ ↑
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.
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 < 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
Transactions¶ ↑
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
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 ActiveRecord's validation framework, custom validators will not work as expected when defined to run in multiple states. For example:
class Vehicle < ActiveRecord::Base 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 < ActiveRecord::Base state_machine do ... state :first_gear, :second_gear do validate {|vehicle| vehicle.speed_is_legal} end end end
Validation errors¶ ↑
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.
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)
Scopes¶ ↑
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')
Note that states can also be referenced by the string version of their name:
Vehicle.with_state('parked')
Callbacks¶ ↑
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.
Failure callbacks¶ ↑
after_failure
callbacks allow you to execute behaviors when a
transition is allowed, but fails to save. This could be useful for
something like auditing transition attempts. Since callbacks run within
transactions in ActiveRecord, a save
failure will cause any records that get created in your callback to roll
back. You can work around this issue like so:
class TransitionLog < ActiveRecord::Base establish_connection Rails.env.to_sym end class Vehicle < ActiveRecord::Base state_machine do after_failure do |vehicle, transition| TransitionLog.create(:vehicle => vehicle, :transition => transition) end ... end end
The TransitionLog
model establishes a second connection to the
database that allows new records to be saved without being affected by
rollbacks in the Vehicle
model's transaction.
Callback Order¶ ↑
Callbacks occur in the following order. Callbacks specific to state_machine are bolded. The remaining callbacks are part of ActiveRecord.
-
(-) save
-
(-) begin transaction (if enabled)
-
(1) before_transition
-
(-) valid
-
(2) before_validation
-
(-) validate
-
(3) after_validation
-
(4) before_save
-
(5) before_create
-
(-) create
-
(6) after_create
-
(7) after_save
-
(8) after_transition
-
(-) end transaction (if enabled)
-
(9) after_commit
Observers¶ ↑
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
Internationalization¶ ↑
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" # %{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}"
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, where
model_name
= “vehicle”, machine_name
= “state”
and state_name
= “parked”:
-
activerecord.state_machines.#{model_name}.#{machine_name}.states.#{state_name}
-
activerecord.state_machines.#{model_name}.states.#{state_name}
-
activerecord.state_machines.#{machine_name}.states.#{state_name}
-
activerecord.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”:
-
activerecord.state_machines.#{model_name}.#{machine_name}.events.#{event_name}
-
activerecord.state_machines.#{model_name}.events.#{event_name}
-
activerecord.state_machines.#{machine_name}.events.#{event_name}
-
activerecord.state_machines.events.#{event_name}
An example translation configuration might look like so:
es: activerecord: state_machines: states: parked: 'estacionado' events: park: 'estacionarse'
Public Class Methods
# File lib/state_machine/integrations/active_record/versions.rb, line 5 def self.active? ::ActiveRecord::VERSION::MAJOR == 2 || ::ActiveRecord::VERSION::MAJOR == 3 && ::ActiveRecord::VERSION::MINOR == 0 end
Classes that inherit from ActiveRecord::Base will automatically use the ActiveRecord integration.
# File lib/state_machine/integrations/active_record.rb, line 421 def self.matching_ancestors %w(ActiveRecord::Base) end
Public Instance Methods
# File lib/state_machine/integrations/active_record/versions.rb, line 107 def ancestors_for(klass) klass.self_and_descendents_from_active_record end
# File lib/state_machine/integrations/active_record/versions.rb, line 97 def default_error_message_options(object, attribute, message) {:default => @messages[message]} end
# File lib/state_machine/integrations/active_record/versions.rb, line 80 def i18n_scope(klass) :activerecord end
# File lib/state_machine/integrations/active_record/versions.rb, line 52 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 25 def load_locale super if defined?(I18n) end
# File lib/state_machine/integrations/active_record/versions.rb, line 84 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 76 def supports_mass_assignment_security? true end
# File lib/state_machine/integrations/active_record/versions.rb, line 68 def supports_observers? true end
# File lib/state_machine/integrations/active_record/versions.rb, line 72 def supports_validations? true end
# File lib/state_machine/integrations/active_record/versions.rb, line 60 def translate(klass, key, value) if defined?(I18n) super else value ? value.to_s.humanize.downcase : 'nil' end end
Protected Instance Methods
Runs state events around the machine's :save action
# File lib/state_machine/integrations/active_record.rb, line 500 def around_save(object) transaction(object) do object.class.state_machines.transitions(object, action).perform { yield } end end
Generates the fully-qualifed column name for this machine's attribute
# File lib/state_machine/integrations/active_record.rb, line 519 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 536 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 508 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 514 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 479 def define_action_hook if action_hook == :save define_helper :instance, " def save(*) self.class.state_machine(#{name.inspect}).send(:around_save, self) { super } end def save!(*) self.class.state_machine(#{name.inspect}).send(:around_save, self) { super } || raise(ActiveRecord::RecordInvalid.new(self)) end def changed_for_autosave? super || self.class.state_machines.any? {|name, machine| machine.action == :save && machine.read(self, :event)} end ", __FILE__, __LINE__ + 1 else super end end
Initializes dynamic states
# File lib/state_machine/integrations/active_record.rb, line 467 def define_dynamic_state_initializer define_helper :instance, " def initialize(*) super do |*args| self.class.state_machines.initialize_states(self, :static => false) yield(*args) if block_given? end end ", __FILE__, __LINE__ + 1 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 446 def define_state_initializer define_static_state_initializer define_dynamic_state_initializer end
Initializes static states
# File lib/state_machine/integrations/active_record.rb, line 452 def define_static_state_initializer # This is the only available hook where the default set of attributes # can be overridden for a new object *prior* to the processing of the # attributes passed into #initialize define_helper :class, " def column_defaults(*) #:nodoc: result = super # No need to pass in an object, since the overrides will be forced self.state_machines.initialize_states(nil, :static => :force, :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 543 def owner_class_ancestor_has_method?(scope, method) scope == :instance && method == "#{attribute}?" ? owner_class : super end
Gets the db default for the machine's attribute
# File lib/state_machine/integrations/active_record.rb, line 437 def owner_class_attribute_default if owner_class.connected? && owner_class.table_exists? && column = owner_class.columns_hash[attribute.to_s] column.default end end
Only runs validations on the action if using :save
# File lib/state_machine/integrations/active_record.rb, line 432 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 527 def transaction(object) result = nil object.class.transaction do raise ::ActiveRecord::Rollback unless result = yield end result end