module StateMachine::Integrations::Mongoid
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'
Public Class Methods
# File lib/state_machine/integrations/mongoid/versions.rb, line 5 def self.active? ::Mongoid::VERSION =~ /^2\./ end
Classes that include Mongoid::Document will automatically use the Mongoid integration.
# File lib/state_machine/integrations/mongoid.rb, line 362 def self.matching_ancestors %w(Mongoid::Document) end
Protected Instance Methods
Runs state events around the machine's :save action
# File lib/state_machine/integrations/mongoid.rb, line 439 def around_save(object) object.class.state_machines.transitions(object, action).perform { yield } end
Gets the field for this machine's attribute (if it exists)
# File lib/state_machine/integrations/mongoid.rb, line 383 def attribute_field owner_class.fields[attribute.to_s] || owner_class.fields[owner_class.aliased_fields[attribute.to_s]] end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/mongoid.rb, line 445 def create_with_scope(name) define_scope(name, lambda {|values| {attribute => {'$in' => values}}}) end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/mongoid.rb, line 451 def create_without_scope(name) define_scope(name, lambda {|values| {attribute => {'$nin' => values}}}) end
Uses around callbacks to run state events if using the :save hook
# File lib/state_machine/integrations/mongoid.rb, line 417 def define_action_hook if action_hook == :save define_helper :instance, " def insert(*) self.class.state_machine(#{name.inspect}).send(:around_save, self) { super.persisted? } self end def update(*) self.class.state_machine(#{name.inspect}).send(:around_save, self) { super } end def upsert(*) self.class.state_machine(#{name.inspect}).send(:around_save, self) { super } end ", __FILE__, __LINE__ + 1 else super end end
Defines a new scope with the given name
# File lib/state_machine/integrations/mongoid.rb, line 456 def define_scope(name, scope) lambda {|model, values| model.criteria.where(scope.call(values))} end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/mongoid.rb, line 411 def define_state_accessor owner_class.field(attribute, :type => String) unless attribute_field super end
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/mongoid.rb, line 390 def define_state_initializer define_helper :instance, " def initialize(*) super do |*args| self.class.state_machines.initialize_states(self, :static => false) yield(*args) if block_given? end end def apply_pre_processed_defaults defaults = {} self.class.state_machines.initialize_states(self, :static => :force, :dynamic => false, :to => defaults) defaults.each do |attr, value| send(:"\#{attr}=", value) unless attributes.include?(attr) end super end ", __FILE__, __LINE__ + 1 end
Gets the db default for the machine's attribute
# File lib/state_machine/integrations/mongoid.rb, line 378 def owner_class_attribute_default attribute_field && attribute_field.default_val end
Only runs validations on the action if using :save
# File lib/state_machine/integrations/mongoid.rb, line 373 def runs_validations_on_action? action == :save end