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.

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.

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')

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.

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"
        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:

Event translations will be looked for using the following keys:

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, line 5
def self.active?
  ::ActiveRecord::VERSION::MAJOR == 2
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, line 328
def self.available?
  defined?(::ActiveRecord::Base)
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, line 335
def self.matches?(klass)
  klass <= ::ActiveRecord::Base
end

Public Instance Methods

action_hook() click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 68
def action_hook
  action == :save ? :create_or_update : super
end
ancestors_for(klass) click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 95
def ancestors_for(klass)
  klass.self_and_descendents_from_active_record
end
default_error_message_options(object, attribute, message) click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 85
def default_error_message_options(object, attribute, message)
  {:default => @messages[message]}
end
i18n_scope(klass) click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 64
def i18n_scope(klass)
  :activerecord
end
invalidate(object, attribute, message, values = []) click to toggle source
# 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
load_locale() click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 9
def load_locale
  super if defined?(I18n)
end
load_observer_extensions() click to toggle source
# 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
supports_dirty_tracking?(object) click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 105
def supports_dirty_tracking?(object)
  false
end
supports_mass_assignment_security?() click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 60
def supports_mass_assignment_security?
  true
end
supports_observers?() click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 52
def supports_observers?
  true
end
supports_validations?() click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 56
def supports_validations?
  true
end
translate(klass, key, value) click to toggle source
# File lib/state_machine/integrations/active_record/versions.rb, line 44
def translate(klass, key, value)
  if defined?(I18n)
    super
  else
    value ? value.to_s.humanize.downcase : 'nil'
  end
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, line 382
def around_save(object)
  object.class.state_machines.transitions(object, action).perform { yield }
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, line 399
def attribute_column
  connection = owner_class.connection
  "#{connection.quote_table_name(owner_class.table_name)}.#{connection.quote_column_name(attribute)}"
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, line 412
def create_scope(name, scope)
  lambda {|model, values| model.where(scope.call(values))}
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, line 388
def create_with_scope(name)
  create_scope(name, lambda {|values| ["#{attribute_column} IN (?)", values]})
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, line 394
def create_without_scope(name)
  create_scope(name, lambda {|values| ["#{attribute_column} NOT IN (?)", values]})
end
define_action_hook() click to toggle source

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
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, 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
owner_class_ancestor_has_method?(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.

# File lib/state_machine/integrations/active_record.rb, line 419
def owner_class_ancestor_has_method?(method)
  method == "#{name}?" || super
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, line 346
def runs_validations_on_action?
  action == :save
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, line 407
def transaction(object)
  object.class.transaction {raise ::ActiveRecord::Rollback unless yield}
end

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