Module: StateMachine::Integrations::MongoMapper

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

Overview

Adds support for integrating state machines with MongoMapper models.

Examples

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

class Vehicle
  include MongoMapper::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: 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 MongoMapper, 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
  include MongoMapper::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 MongoMapper::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

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 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 MongoMapper::Document

  def self.with_states(*states)
    all(:conditions => {:state => {'$in' => states}})
  end
  # with_states also aliased to with_state

  def self.without_states(*states)
    all(:conditions => {:state => {'$nin' => states}})
  end
  # 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 MongoMapper, they cannot be chained.

Callbacks

All before/after transition callbacks defined for MongoMapper models behave in the same way that other MongoMapper callbacks behave. The object involved in the transition is passed in as an argument.

For example,

class Vehicle
  include MongoMapper::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.

Instance Attribute Summary

Attributes included from Base::ClassMethods

#defaults

Class Method Summary collapse

Methods included from ActiveModel

included, #invalidate, #reset, #write

Methods included from ClassMethods

extended, #state_machines

Methods included from Base

included

Methods included from Base::ClassMethods

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

Class Method Details

.available? ⇒ Boolean

Whether this integration is available. Only true if MongoMapper::Document is defined.

Returns:

  • (Boolean) 


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# File 'lib/state_machine/integrations/mongo_mapper.rb', line 199

def self.available?
  defined?(::MongoMapper::Document)
end

.matches?(klass) ⇒ Boolean

Should this integration be used for state machines in the given class? Classes that include MongoMapper::Document will automatically use the MongoMapper integration.

Returns:

  • (Boolean) 


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# File 'lib/state_machine/integrations/mongo_mapper.rb', line 206

def self.matches?(klass)
  klass <= ::MongoMapper::Document
end