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:

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

If using the save action for the machine, this option will be ignored as the transaction will be created by ActiveRecord within save. To avoid this, use a different action like so:

class Vehicle < ActiveRecord::Base
  state_machine :initial => :parked, :use_transactions => false, :action => :save_state do
    ...
  end

  alias_method :save_state, :save
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.

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:

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”:

Event translations will be looked for using the following keys, where model_name = “vehicle”, machine_name = “state” and event_name = “ignite”:

An example translation configuration might look like so:

es:
  activerecord:
    state_machines:
      states:
        parked: 'estacionado'
      events:
        park: 'estacionarse'

Public Class Methods

active?() click to toggle source
  # File lib/state_machine/integrations/active_record/versions.rb
5 def self.active?
6   ::ActiveRecord::VERSION::MAJOR == 2 || ::ActiveRecord::VERSION::MAJOR == 3 && ::ActiveRecord::VERSION::MINOR == 0
7 end
available?() click to toggle source

Whether this integration is available. Only true if ActiveRecord::Base is defined.

    # File lib/state_machine/integrations/active_record.rb
412 def self.available?
413   defined?(::ActiveRecord::Base)
414 end
matches?(klass) click to toggle source

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
419 def self.matches?(klass)
420   klass <= ::ActiveRecord::Base
421 end

Public Instance Methods

action_hook() click to toggle source
Calls superclass method
   # File lib/state_machine/integrations/active_record/versions.rb
84 def action_hook
85   action == :save ? :create_or_update : super
86 end
ancestors_for(klass) click to toggle source
    # File lib/state_machine/integrations/active_record/versions.rb
111 def ancestors_for(klass)
112   klass.self_and_descendents_from_active_record
113 end
default_error_message_options(object, attribute, message) click to toggle source
    # File lib/state_machine/integrations/active_record/versions.rb
101 def default_error_message_options(object, attribute, message)
102   {:default => @messages[message]}
103 end
i18n_scope(klass) click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
80 def i18n_scope(klass)
81   :activerecord
82 end
invalidate(object, attribute, message, values = []) click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
52 def invalidate(object, attribute, message, values = [])
53   if defined?(I18n)
54     super
55   else
56     object.errors.add(self.attribute(attribute), generate_message(message, values))
57   end
58 end
load_locale() click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
25 def load_locale
26   super if defined?(I18n)
27 end
load_observer_extensions() click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
88 def load_observer_extensions
89   super
90   ::ActiveRecord::Observer.class_eval do
91     include StateMachine::Integrations::ActiveModel::Observer
92   end unless ::ActiveRecord::Observer < StateMachine::Integrations::ActiveModel::Observer
93 end
supports_mass_assignment_security?() click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
76 def supports_mass_assignment_security?
77   true
78 end
supports_observers?() click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
68 def supports_observers?
69   true
70 end
supports_validations?() click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
72 def supports_validations?
73   true
74 end
translate(klass, key, value) click to toggle source
   # File lib/state_machine/integrations/active_record/versions.rb
60 def translate(klass, key, value)
61   if defined?(I18n)
62     super
63   else
64     value ? value.to_s.humanize.downcase : 'nil'
65   end
66 end

Protected Instance Methods

around_save(object) { || ... } click to toggle source

Runs state events around the machine's :save action

    # File lib/state_machine/integrations/active_record.rb
479 def around_save(object)
480   object.class.state_machines.transitions(object, action).perform { yield }
481 end
attribute_column() click to toggle source

Generates the fully-qualifed column name for this machine's attribute

    # File lib/state_machine/integrations/active_record.rb
496 def attribute_column
497   connection = owner_class.connection
498   "#{connection.quote_table_name(owner_class.table_name)}.#{connection.quote_column_name(attribute)}"
499 end
create_scope(name, scope) click to toggle source

Defines a new named scope with the given name

    # File lib/state_machine/integrations/active_record.rb
509 def create_scope(name, scope)
510   lambda {|model, values| model.where(scope.call(values))}
511 end
create_with_scope(name) click to toggle source

Creates a scope for finding records with a particular state or states for the attribute

    # File lib/state_machine/integrations/active_record.rb
485 def create_with_scope(name)
486   create_scope(name, lambda {|values| ["#{attribute_column} IN (?)", values]})
487 end
create_without_scope(name) click to toggle source

Creates a scope for finding records without a particular state or states for the attribute

    # File lib/state_machine/integrations/active_record.rb
491 def create_without_scope(name)
492   create_scope(name, lambda {|values| ["#{attribute_column} NOT IN (?)", values]})
493 end
define_action_hook() click to toggle source

Uses around callbacks to run state events if using the :save hook

Calls superclass method
    # File lib/state_machine/integrations/active_record.rb
470 def define_action_hook
471   if action_hook == :save
472     owner_class.set_callback(:save, :around, self, :prepend => true)
473   else
474     super
475   end
476 end
define_dynamic_state_initializer() click to toggle source

Initializes dynamic states

    # File lib/state_machine/integrations/active_record.rb
458         def define_dynamic_state_initializer
459           define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1
460             def initialize(*)
461               super do |*args|
462                 self.class.state_machines.initialize_states(self, :static => false)
463                 yield(*args) if block_given?
464               end
465             end
466           end_eval
467         end
define_state_initializer() click to toggle source

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
437 def define_state_initializer
438   define_static_state_initializer
439   define_dynamic_state_initializer
440 end
define_static_state_initializer() click to toggle source

Initializes static states

    # File lib/state_machine/integrations/active_record.rb
443         def define_static_state_initializer
444           # This is the only available hook where the default set of attributes
445           # can be overridden for a new object *prior* to the processing of the
446           # attributes passed into #initialize
447           define_helper :class, <<-end_eval, __FILE__, __LINE__ + 1
448             def column_defaults(*) #:nodoc:
449               result = super
450               # No need to pass in an object, since the overrides will be forced
451               self.state_machines.initialize_states(nil, :dynamic => false, :to => result)
452               result
453             end
454           end_eval
455         end
owner_class_ancestor_has_method?(scope, method) click to toggle source

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.

Calls superclass method
    # File lib/state_machine/integrations/active_record.rb
516 def owner_class_ancestor_has_method?(scope, method)
517   scope == :instance && method == "#{attribute}?" ? owner_class : super
518 end
runs_validations_on_action?() click to toggle source

Only runs validations on the action if using :save

    # File lib/state_machine/integrations/active_record.rb
430 def runs_validations_on_action?
431   action == :save
432 end
transaction(object) { || ... } click to toggle source

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
504 def transaction(object)
505   object.class.transaction {raise ::ActiveRecord::Rollback unless yield}
506 end