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
If using the save
action for the machine, this option will be ignored as the transaction will be created by Sequel
within save
. To avoid this, use a different action like so:
class Vehicle < Sequel::Model 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 @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.
Attributes
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
Whether this integration is available. Only true if Sequel::Model is defined.
# File lib/state_machine/integrations/sequel.rb 279 def self.available? 280 defined?(::Sequel::Model) 281 end
Should this integration be used for state machines in the given class? Classes that include Sequel::Model will automatically use the Sequel
integration.
# File lib/state_machine/integrations/sequel.rb 286 def self.matches?(klass) 287 klass <= ::Sequel::Model 288 end
Public Instance Methods
# File lib/state_machine/integrations/sequel/versions.rb 44 def define_action_hook 45 if action == :save 46 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 47 def #{action_hook}(*) 48 yielded = false 49 result = self.class.state_machines.transitions(self, :save).perform do 50 yielded = true 51 super 52 end 53 54 if yielded || result 55 result 56 else 57 #{handle_save_failure} 58 end 59 end 60 end_eval 61 else 62 super 63 end 64 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/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 100 def handle_save_failure 101 'save_failure(:save)' 102 end
# File lib/state_machine/integrations/sequel/versions.rb 96 def handle_validation_failure 97 'raise_on_save_failure ? save_failure(:validation) : result' 98 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
Uses internal save hooks if using the :save action
# File lib/state_machine/integrations/sequel.rb 379 def action_hook 380 action == :save ? :around_save : super 381 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 Sequel
callbacks
# File lib/state_machine/integrations/sequel.rb 430 def add_callback(type, options, &block) 431 options[:bind_to_object] = true 432 options[:terminator] = @terminator ||= lambda {|result| result == false} 433 super 434 end
Generates the fully-qualifed column name for this machine's attribute
# File lib/state_machine/integrations/sequel.rb 417 def attribute_column 418 ::Sequel::SQL::QualifiedIdentifier.new(owner_class.table_name, attribute) 419 end
Creates a new named scope with the given name
# File lib/state_machine/integrations/sequel.rb 396 def create_scope(name, scope) 397 machine = self 398 owner_class.def_dataset_method(name) do |*states| 399 machine.send(:run_scope, scope, self, states) 400 end 401 402 false 403 end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb 385 def create_with_scope(name) 386 create_scope(name, lambda {|dataset, values| dataset.filter(attribute_column => values)}) 387 end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb 391 def create_without_scope(name) 392 create_scope(name, lambda {|dataset, values| dataset.exclude(attribute_column => values)}) 393 end
Defines validation hooks if the machine's action is to save the model
# File lib/state_machine/integrations/sequel.rb 364 def define_action_helpers 365 super 366 define_validation_hook if action == :save 367 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 355 def define_state_accessor 356 name = self.name 357 owner_class.validates_each(attribute) do |record, attr, value| 358 machine = record.class.state_machine(name) 359 machine.invalidate(record, :state, :invalid) unless machine.states.match(record) 360 end 361 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 346 def define_state_initializer 347 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 348 def initialize_set(*) 349 self.class.state_machines.initialize_states(self) { super } 350 end 351 end_eval 352 end
Adds hooks into validation for automatically firing events
# File lib/state_machine/integrations/sequel.rb 370 def define_validation_hook 371 define_helper :instance, <<-end_eval, __FILE__, __LINE__ + 1 372 def around_validation(*) 373 self.class.state_machines.transitions(self, :save, :after => false).perform { super } 374 end 375 end_eval 376 end
Loads the built-in inflector
# File lib/state_machine/integrations/sequel.rb 339 def load_inflector 340 require 'sequel/extensions/inflector' 341 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(:validation_class_methods) 335 owner_class.plugin(:hook_class_methods) 336 end
Determines the model associated with the given dataset
# File lib/state_machine/integrations/sequel.rb 412 def model_from_dataset(dataset) 413 dataset.model 414 end
Generates the results for the given scope based on one or more states to filter by
# File lib/state_machine/integrations/sequel.rb 407 def run_scope(scope, dataset, states) 408 super(scope, model_from_dataset(dataset).state_machine(name), dataset, states) 409 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 423 def transaction(object) 424 object.db.transaction {raise ::Sequel::Error::Rollback unless yield} 425 end