Module: StateMachine::Integrations::Mongoid

Includes:
ActiveModel, Base
Defined in:
lib/state_machine/integrations/mongoid.rb,
lib/state_machine/integrations/mongoid/versions.rb

Overview

Adds support for integrating state machines with Mongoid models.

Examples

Below is an example of a simple state machine defined within a Mongoid model:

class Vehicle
  include Mongoid::Document

  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: 4d70e028b876bb54d9000003, name: nil, state: "parked">
vehicle.name = 'Ford Explorer'
vehicle.ignite                    # => true
vehicle.reload                    # => #<Vehicle _id: 4d70e028b876bb54d9000003, 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 Mongoid, 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: 4d70e028b876bb54d9000003, 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: 4d70e028b876bb54d9000003, 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
  include Mongoid::Document

  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 Mongoid::Document

  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

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 Mongoid’s validation framework, custom validators will not work as expected when defined to run in multiple states. For example:

class Vehicle
  include Mongoid::Document

  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
  include Mongoid::Document

  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: 4d70e028b876bb54d9000003, 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 basic scopes are defined on the model for finding records with or without a particular set of states.

These scopes are essentially the functional equivalent of the following definitions:

class Vehicle
  include Mongoid::Document

  scope :with_states, lambda {|*states| where(:state => {'$in' => states})}
  # with_states also aliased to with_state

  scope :without_states, lambda {|*states| where(:state => {'$nin' => 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 Mongoid, they cannot be chained.

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 Mongoid models behave in the same way that other Mongoid callbacks behave. The object involved in the transition is passed in as an argument.

For example,

class Vehicle
  include Mongoid::Document

  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 Mongoid-like hooks, there is additional support for Mongoid observers. Because of the way Mongoid 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 < Mongoid::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 < Mongoid::Observer
  observe Vehicle, Switch, Project

  def after_transition(record, transition)
    Audit.log(record, transition)
  end
end

Callback Order

Callbacks occur in the following order. Callbacks specific to state_machine are bolded. The remaining callbacks are part of Mongoid.

  • (-) save

  • (1) before_transition

  • (-) valid

  • (2) before_validation

  • (3) after_validation

  • (4) before_save

  • (5) before_create

  • (6) after_create

  • (7) after_save

  • (8) after_transition

Internationalization

Any error message that is generated from performing invalid transitions can be localized. The following default translations are used:

en:
  mongoid:
    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}"

You can override these for a specific model like so:

en:
  mongoid:
    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”:

  • mongoid.state_machines.#{model_name}.#{machine_name}.states.#{state_name}

  • mongoid.state_machines.#{model_name}.states.#{state_name}

  • mongoid.state_machines.#{machine_name}.states.#{state_name}

  • mongoid.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”:

  • mongoid.state_machines.#{model_name}.#{machine_name}.events.#{event_name}

  • mongoid.state_machines.#{model_name}.events.#{event_name}

  • mongoid.state_machines.#{machine_name}.events.#{event_name}

  • mongoid.state_machines.events.#{event_name}

An example translation configuration might look like so:

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

Instance Attribute Summary

Attributes included from Base::ClassMethods

#defaults

Class Method Summary collapse

Methods included from ActiveModel

#errors_for, included, #invalidate, #reset

Methods included from ClassMethods

#state_machines

Methods included from Base

included

Methods included from Base::ClassMethods

#available?, #extended, #integration_name, #locale_path, #matches?, #matches_ancestors?, #matching_ancestors, #version, #versions

Class Method Details

.extended(base) ⇒ Object

:nodoc:



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# File 'lib/state_machine/integrations/mongoid.rb', line 366

def self.extended(base) #:nodoc:
  require 'mongoid/version'
  super
end

.matching_ancestors ⇒ Object

Classes that include Mongoid::Document will automatically use the Mongoid integration.



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# File 'lib/state_machine/integrations/mongoid.rb', line 362

def self.matching_ancestors
  %w(Mongoid::Document)
end