Module StateMachine::Integrations::MongoMapper
In: lib/state_machine/integrations/mongo_mapper.rb
lib/state_machine/integrations/mongo_mapper/versions.rb

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.

Methods

Included Modules

Base ActiveModel

Public Class methods

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

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

Public Instance methods

Protected Instance methods

Runs state events around the machine‘s :save action

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

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

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

Defines a new scope with the given name

Skips defining reader/writer methods since this is done automatically

Defines an initialization hook into the owner class for setting the initial state of the machine before any attributes are set on the object

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.

Only runs validations on the action if using :save

[Validate]