Module | StateMachine::Integrations::Mongoid |
In: |
lib/state_machine/integrations/mongoid.rb
lib/state_machine/integrations/mongoid/versions.rb |
Adds support for integrating state machines with Mongoid models.
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.
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">
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:
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.
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
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.
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.
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.
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:
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
Should this integration be used for state machines in the given class? Classes that include Mongoid::Document will automatically use the Mongoid integration.
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.
Mongoid uses its own implementation of dirty tracking instead of ActiveModel‘s and doesn‘t support the #{attribute}_will_change! APIs