module StateMachine::Integrations::Sequel
Adds support for integrating state machines with Sequel
models.
Examples¶ ↑
Below is an example of a simple state machine defined within a Sequel
model:
class Vehicle < Sequel::Model 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 made as well.
For example,
vehicle = Vehicle.create # => #<Vehicle @values={:state=>"parked", :name=>nil, :id=>1}> vehicle.name = 'Ford Explorer' vehicle.ignite # => true vehicle.refresh # => #<Vehicle @values={:state=>"idling", :name=>"Ford Explorer", :id=>1}>
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 Sequel
, 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 @values={:state=>"parked", :name=>nil, :id=>1}> 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 # => #<Vehicle @values={:state=>"idling", :name=>nil, :id=>1}> 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 @values={:state=>"idling", :name=>nil, :id=>1}> 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 < Sequel::Model set_restricted_columns :state_event # set_allowed_columns ... # 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 < Sequel::Model set_restricted_columns :state_event # Prevent access to events in the first machine state_machine do # Define private events here end # Allow both machines to share the same state state_machine :public_state, :attribute => :state do # Define public events here end end
Transactions¶ ↑
In order to ensure that any changes made during transition callbacks are rolled back during a failed attempt, every transition is wrapped within a transaction.
For example,
class Message < Sequel::Model end Vehicle.state_machine do before_transition do |transition| Message.create(:content => transition.inspect) false end end vehicle = Vehicle.create # => #<Vehicle @values={:state=>"parked", :name=>nil, :id=>1}> vehicle.ignite # => false Message.count # => 0
Note that only before callbacks that halt the callback chain and failed attempts to save the record will result in the transaction being rolled back. If an after callback halts the chain, the previous result still applies and the transaction is not rolled back.
To turn off transactions:
class Vehicle < Sequel::Model state_machine :initial => :parked, :use_transactions => false do ... 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 @values={:state=>"parked", :name=>nil, :id=>1}> 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 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 < Sequel::Model class << self def with_states(*states) filter(:state => states) end alias_method :with_state, :with_states def without_states(*states) filter(~{:state => states}) 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 Sequel
, they can be chained like so:
Vehicle.with_state(:parked).order(:id.desc)
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 Sequel
resources behave in the same way that other Sequel
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 < Sequel::Model 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.
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 Sequel
, a save failure will cause any records that get created in your callback to roll back. You can work around this issue like so:
DB = Sequel.connect('mysql://localhost/app') DB_LOGS = Sequel.connect('mysql://localhost/app') class TransitionLog < Sequel::Model(DB_LOGS[:transition_logs]) end class Vehicle < Sequel::Model(DB[:vehicles]) state_machine do after_failure do |transition| TransitionLog.create(:vehicle => vehicle, :transition => transition) end ... end end
The TransitionLog
model uses a second connection to the database that allows new records to be saved without being affected by rollbacks in the Vehicle
model’s transaction.
Callback
Order¶ ↑
Callbacks occur in the following order. Callbacks specific to state_machine are bolded. The remaining callbacks are part of Sequel
.
-
(-) save
-
(-) begin transaction (if enabled)
-
(1) before_transition
-
(2) before_validation
-
(-) validate
-
(3) after_validation
-
(4) before_save
-
(5) before_create
-
(-) create
-
(6) after_create
-
(7) after_save
-
(8) after_transition
-
(-) end transaction (if enabled)
-
(9) after_commit
Public Class Methods
# File lib/state_machine/integrations/sequel/versions.rb 5 def self.active? 6 !defined?(::Sequel::MAJOR) || ::Sequel::MAJOR == 2 || ::Sequel::MAJOR == 3 && ::Sequel::MINOR <= 23 7 end
Classes that include Sequel::Model will automatically use the Sequel
integration.
# File lib/state_machine/integrations/sequel.rb 286 def self.matching_ancestors 287 %w(Sequel::Model) 288 end
Public Instance Methods
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/sequel.rb 310 def errors_for(object) 311 object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', ' 312 end
# File lib/state_machine/integrations/sequel/versions.rb 51 def handle_validation_failure 52 'raise_on_save_failure ? save_failure(:validation) : result' 53 end
Adds a validation error to the given object
# File lib/state_machine/integrations/sequel.rb 304 def invalidate(object, attribute, message, values = []) 305 object.errors.add(self.attribute(attribute), generate_message(message, values)) 306 end
Pluralizes the name using the built-in inflector
# File lib/state_machine/integrations/sequel.rb 320 def pluralize(word) 321 load_inflector 322 super 323 end
Resets any errors previously added when invalidating the given object
# File lib/state_machine/integrations/sequel.rb 315 def reset(object) 316 object.errors.clear 317 end
Forces the change in state to be recognized regardless of whether the state value actually changed
# File lib/state_machine/integrations/sequel.rb 292 def write(object, attribute, value, *args) 293 result = super 294 295 column = self.attribute.to_sym 296 if (attribute == :state || attribute == :event && value) && owner_class.columns.include?(column) && !object.changed_columns.include?(column) 297 object.changed_columns << column 298 end 299 300 result 301 end
Protected Instance Methods
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 Sequel
callbacks
# File lib/state_machine/integrations/sequel.rb 479 def add_callback(type, options, &block) 480 options[:bind_to_object] = true 481 options[:terminator] = @terminator ||= lambda {|result| result == false} 482 super 483 end
Runs state events around the machine’s :save action
# File lib/state_machine/integrations/sequel.rb 400 def around_save(object) 401 result = transaction(object) do 402 object.class.state_machines.transitions(object, action).perform { yield } 403 end 404 result 405 end
Generates the fully-qualifed column name for this machine’s attribute
# File lib/state_machine/integrations/sequel.rb 462 def attribute_column 463 ::Sequel::SQL::QualifiedIdentifier.new(owner_class.table_name, attribute) 464 end
Creates a new named scope with the given name
# File lib/state_machine/integrations/sequel.rb 441 def create_scope(name, scope) 442 machine = self 443 owner_class.def_dataset_method(name) do |*states| 444 machine.send(:run_scope, scope, self, states) 445 end 446 447 false 448 end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb 430 def create_with_scope(name) 431 create_scope(name, lambda {|dataset, values| dataset.filter(attribute_column => values)}) 432 end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb 436 def create_without_scope(name) 437 create_scope(name, lambda {|dataset, values| dataset.exclude(attribute_column => values)}) 438 end
Defines validation hooks if the machine’s action is to save the model
# File lib/state_machine/integrations/sequel.rb 365 def define_action_helpers 366 super 367 define_validation_hook if action == :save 368 end
Uses around callbacks to run state events if using the :save hook
# File lib/state_machine/integrations/sequel.rb 371 def define_action_hook 372 if action == :save 373 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 374 def #{action_hook}(*args) 375 opts = args.last.is_a?(Hash) ? args.last : {} 376 yielded = false 377 result = self.class.state_machine(#{name.inspect}).send(:around_save, self) do 378 yielded = true 379 super 380 end 381 382 if yielded || result 383 result 384 else 385 #{handle_save_failure} 386 end 387 end 388 end_eval 389 else 390 super 391 end 392 end
Initializes class-level extensions for this machine
# File lib/state_machine/integrations/sequel.rb 327 def define_helpers 328 load_plugins 329 super 330 end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/sequel.rb 354 def define_state_accessor 355 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 356 def validate(*) 357 super 358 machine = self.class.state_machine(#{name.inspect}) 359 machine.invalidate(self, :state, :invalid) unless machine.states.match(self) 360 end 361 end_eval 362 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/sequel.rb 345 def define_state_initializer 346 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 347 def initialize_set(*) 348 self.class.state_machines.initialize_states(self, :static => :force) { super } 349 end 350 end_eval 351 end
Adds hooks into validation for automatically firing events
# File lib/state_machine/integrations/sequel.rb 408 def define_validation_hook 409 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 410 def around_validation(*) 411 self.class.state_machines.transitions(self, :save, :after => false).perform { super } 412 end 413 end_eval 414 end
Handles how save failures (due to invalid transitions) are raised
# File lib/state_machine/integrations/sequel.rb 395 def handle_save_failure 396 'raise_hook_failure(:before_transition) if raise_on_failure?(opts)' 397 end
Loads the built-in inflector
# File lib/state_machine/integrations/sequel.rb 338 def load_inflector 339 require 'sequel/extensions/inflector' 340 end
Loads all of the Sequel
plugins necessary to run
# File lib/state_machine/integrations/sequel.rb 333 def load_plugins 334 owner_class.plugin(:hook_class_methods) 335 end
Determines the model associated with the given dataset
# File lib/state_machine/integrations/sequel.rb 457 def model_from_dataset(dataset) 458 dataset.model 459 end
Gets the db default for the machine’s attribute
# File lib/state_machine/integrations/sequel.rb 417 def owner_class_attribute_default 418 if owner_class.db.table_exists?(owner_class.table_name) && column = owner_class.db_schema[attribute.to_sym] 419 column[:default] 420 end 421 end
Uses the DB literal to match the default against the specified state
# File lib/state_machine/integrations/sequel.rb 424 def owner_class_attribute_default_matches?(state) 425 owner_class.db.literal(state.value) == owner_class_attribute_default 426 end
Generates the results for the given scope based on one or more states to filter by
# File lib/state_machine/integrations/sequel.rb 452 def run_scope(scope, dataset, states) 453 super(scope, model_from_dataset(dataset).state_machine(name), dataset, states) 454 end
Runs a new database transaction, rolling back any changes if the yielded block fails (i.e. returns false).
# File lib/state_machine/integrations/sequel.rb 468 def transaction(object) 469 result = nil 470 object.db.transaction do 471 raise ::Sequel::Error::Rollback unless result = yield 472 end 473 result 474 end