module StateMachine::Integrations::DataMapper
Adds support for integrating state machines with DataMapper
resources.
Examples¶ ↑
Below is an example of a simple state machine defined within a DataMapper
resource:
class Vehicle include DataMapper::Resource property :id, Serial property :name, String property :state, String 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 resource to save the changes made to the state machine's attribute. Note that if any other changes were made to the resource 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 DataMapper
, these automated events are run in the following order:
-
before validation - If validation feature loaded, run before callbacks and persist new states, then validate
-
before save - If validation feature was skipped/not loaded, 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 # => #<DataMapper::Validate::ValidationErrors:0xb7a48b54 @errors={"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 DataMapper::Resource ... state_machine do ... end protected :state_event 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 DataMapper::Resource ... state_machine do # Define private events here end protected :state_event= # Prevent access to events in the first machine # Allow both machines to share the same state state_machine :public_state, :attribute => :state do # Define public events here end end
Transactions¶ ↑
By default, the use of transactions during an event transition is turned off to be consistent with DataMapper
. This means that if changes are made to the database during a before callback, but the transition fails to complete, those changes will not be rolled back.
For example,
class Message include DataMapper::Resource property :id, Serial property :content, String end Vehicle.state_machine do before_transition do |transition| Message.create(:content => transition.inspect) throw :halt end end vehicle = Vehicle.create # => #<Vehicle id=1 name=nil state="parked"> vehicle.ignite # => false Message.all.count # => 1
To turn on transactions:
class Vehicle include DataMapper::Resource ... state_machine :initial => :parked, :use_transactions => true do ... end end
If using the save
action for the machine, this option will be ignored as the transaction behavior will depend on the save
implementation within DataMapper
. To avoid this, use a different action like so:
class Vehicle include DataMapper::Resource ... state_machine :initial => :parked, :use_transactions => false, :action => :save_state do ... end alias_method :save_state, :save 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 # => ["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 class methods are defined on the model for finding records with or without a particular set of states.
These named scopes are the functional equivalent of the following definitions:
class Vehicle include DataMapper::Resource property :id, Serial property :state, String class << self def with_states(*states) all(:state => states.flatten) end alias_method :with_state, :with_states def without_states(*states) all(:state.not => states.flatten) end alias_method :without_state, :without_states end end
Note, however, that the states are converted to their stored values before being passed into the query.
Because of the way scopes work in DataMapper
, they can be chained like so:
Vehicle.with_state(:parked).all(:order => [:id.desc])
Note that states can also be referenced by the string version of their name:
Vehicle.with_state('parked')
Callbacks / Observers¶ ↑
All before/after transition callbacks defined for DataMapper
resources behave in the same way that other DataMapper
hooks behave. Rather than passing in the record as an argument to the callback, the callback is instead bound to the object and evaluated within its context.
For example,
class Vehicle include DataMapper::Resource property :id, Serial property :state, String state_machine :initial => :parked do before_transition any => :idling do put_on_seatbelt end before_transition do |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 DataMapper-like hooks, there is additional support for DataMapper
observers. See StateMachine::Integrations::DataMapper::Observer
for more information.
Failure callbacks¶ ↑
after_failure
callbacks allow you to execute behaviors when a transition is allowed, but fails to save. This could be useful for something like auditing transition attempts. Since callbacks run within transactions in DataMapper
, a save failure will cause any records that get created in your callback to roll back. Note that this is only a problem if the machine is configured to use transactions. If it is, you can work around this issue like so:
DataMapper.setup(:default, 'mysql://localhost/app') DataMapper.setup(:logs, 'mysql://localhost/app') class TransitionLog include DataMapper::Resource end class Vehicle < ActiveRecord::Base include DataMapper::Resource state_machine :use_transactions => true do after_failure do |transition| DataMapper.repository(:logs) do TransitionLog.create(:vehicle => vehicle, :transition => transition) end end ... end end
The failure callback creates TransitionLog
records using a second connection to the database, allowing them to be saved without being affected by rollbacks in the Vehicle
resource's transaction.
Attributes
Public Class Methods
# File lib/state_machine/integrations/data_mapper/versions.rb 5 def self.active? 6 ::DataMapper::VERSION =~ /^0\.9\./ 7 end
Whether this integration is available. Only true if DataMapper::Resource is defined.
# File lib/state_machine/integrations/data_mapper.rb 316 def self.available? 317 defined?(::DataMapper::Resource) 318 end
Should this integration be used for state machines in the given class? Classes that include DataMapper::Resource will automatically use the DataMapper
integration.
# File lib/state_machine/integrations/data_mapper.rb 323 def self.matches?(klass) 324 klass <= ::DataMapper::Resource 325 end
Public Instance Methods
0.9.4 - 0.9.6 fails to run after callbacks when validations are enabled because of the way dm-validations integrates
# File lib/state_machine/integrations/data_mapper/versions.rb 31 def define_action_helpers? 32 super if action != :save || !supports_validations? 33 end
Describes the current validation errors on the given object. If none are specific, then the default error is interpeted as a “halt”.
# File lib/state_machine/integrations/data_mapper.rb 340 def errors_for(object) 341 if object.errors.empty? 342 'Transition halted' 343 else 344 errors = [] 345 object.errors.each_pair do |field_name, field_errors| 346 field_errors.each {|error| errors << "#{field_name} #{error}"} 347 end 348 errors * ', ' 349 end 350 end
Adds a validation error to the given object
# File lib/state_machine/integrations/data_mapper.rb 334 def invalidate(object, attribute, message, values = []) 335 object.errors.add(self.attribute(attribute), generate_message(message, values)) if supports_validations? 336 end
Resets any errors previously added when invalidating the given object
# File lib/state_machine/integrations/data_mapper.rb 353 def reset(object) 354 object.errors.clear if supports_validations? 355 end
Protected Instance Methods
Uses internal save hooks if using the :save action
# File lib/state_machine/integrations/data_mapper.rb 417 def action_hook 418 action == :save ? :save_self : super 419 end
Creates a new callback in the callback chain, always ensuring that it's configured to bind to the object as this is the convention for DataMapper/Extlib callbacks
# File lib/state_machine/integrations/data_mapper.rb 442 def add_callback(type, options, &block) 443 options[:bind_to_object] = true 444 super 445 end
Initializes class-level extensions and defaults for this machine
# File lib/state_machine/integrations/data_mapper.rb 359 def after_initialize 360 super 361 load_observer_extensions 362 end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/data_mapper.rb 423 def create_with_scope(name) 424 lambda {|resource, values| resource.all(attribute => values)} 425 end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/data_mapper.rb 429 def create_without_scope(name) 430 lambda {|resource, values| resource.all(attribute.to_sym.not => values)} 431 end
Adds hooks into validation for automatically firing events
# File lib/state_machine/integrations/data_mapper.rb 404 def define_action_helpers 405 super 406 407 if action == :save && supports_validations? 408 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 409 def valid?(*) 410 self.class.state_machines.transitions(self, :save, :after => false).perform { super } 411 end 412 end_eval 413 end 414 end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/data_mapper.rb 391 def define_state_accessor 392 owner_class.property(attribute, String) unless owner_class.properties.detect {|property| property.name == attribute} 393 394 if supports_validations? 395 name = self.name 396 owner_class.validates_with_block(attribute) do 397 machine = self.class.state_machine(name) 398 machine.states.match(self) ? true : [false, machine.generate_message(:invalid)] 399 end 400 end 401 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/data_mapper.rb 382 def define_state_initializer 383 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 384 def initialize(*args) 385 self.class.state_machines.initialize_states(self) { super } 386 end 387 end_eval 388 end
Loads extensions to DataMapper's Observers
# File lib/state_machine/integrations/data_mapper.rb 365 def load_observer_extensions 366 require 'state_machine/integrations/data_mapper/observer' if ::DataMapper.const_defined?('Observer') 367 end
Pluralizes the name using the built-in inflector
# File lib/state_machine/integrations/data_mapper.rb 375 def pluralize(word) 376 ::DataMapper::Inflector.pluralize(word.to_s) 377 end
Is validation support currently loaded?
# File lib/state_machine/integrations/data_mapper.rb 370 def supports_validations? 371 @supports_validations ||= ::DataMapper.const_defined?('Validate') 372 end
Runs a new database transaction, rolling back any changes if the yielded block fails (i.e. returns false).
# File lib/state_machine/integrations/data_mapper.rb 435 def transaction(object) 436 object.class.transaction {|t| t.rollback unless yield} 437 end