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, line 5 def self.active? !defined?(::Sequel::MAJOR) || ::Sequel::MAJOR == 2 || ::Sequel::MAJOR == 3 && ::Sequel::MINOR <= 23 end
Classes that include Sequel::Model will automatically use the Sequel integration.
# File lib/state_machine/integrations/sequel.rb, line 286 def self.matching_ancestors %w(Sequel::Model) 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, line 310 def errors_for(object) object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', ' end
# File lib/state_machine/integrations/sequel/versions.rb, line 51 def handle_validation_failure 'raise_on_save_failure ? save_failure(:validation) : result' end
Adds a validation error to the given object
# File lib/state_machine/integrations/sequel.rb, line 304 def invalidate(object, attribute, message, values = []) object.errors.add(self.attribute(attribute), generate_message(message, values)) end
Pluralizes the name using the built-in inflector
# File lib/state_machine/integrations/sequel.rb, line 320 def pluralize(word) load_inflector super end
Resets any errors previously added when invalidating the given object
# File lib/state_machine/integrations/sequel.rb, line 315 def reset(object) object.errors.clear end
Forces the change in state to be recognized regardless of whether the state value actually changed
# File lib/state_machine/integrations/sequel.rb, line 292 def write(object, attribute, value, *args) result = super column = self.attribute.to_sym if (attribute == :state || attribute == :event && value) && owner_class.columns.include?(column) && !object.changed_columns.include?(column) object.changed_columns << column end result 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, line 479 def add_callback(type, options, &block) options[:bind_to_object] = true options[:terminator] = @terminator ||= lambda {|result| result == false} super end
Runs state events around the machine's :save action
# File lib/state_machine/integrations/sequel.rb, line 400 def around_save(object) result = transaction(object) do object.class.state_machines.transitions(object, action).perform { yield } end result end
Generates the fully-qualifed column name for this machine's attribute
# File lib/state_machine/integrations/sequel.rb, line 462 def attribute_column ::Sequel::SQL::QualifiedIdentifier.new(owner_class.table_name, attribute) end
Creates a new named scope with the given name
# File lib/state_machine/integrations/sequel.rb, line 441 def create_scope(name, scope) machine = self owner_class.def_dataset_method(name) do |*states| machine.send(:run_scope, scope, self, states) end false end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb, line 430 def create_with_scope(name) create_scope(name, lambda {|dataset, values| dataset.filter(attribute_column => values)}) end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/sequel.rb, line 436 def create_without_scope(name) create_scope(name, lambda {|dataset, values| dataset.exclude(attribute_column => values)}) end
Defines validation hooks if the machine's action is to save the model
# File lib/state_machine/integrations/sequel.rb, line 365 def define_action_helpers super define_validation_hook if action == :save end
Uses around callbacks to run state events if using the :save hook
# File lib/state_machine/integrations/sequel.rb, line 371 def define_action_hook if action == :save define_helper :instance, " def #{action_hook}(*args) opts = args.last.is_a?(Hash) ? args.last : {} yielded = false result = self.class.state_machine(#{name.inspect}).send(:around_save, self) do yielded = true super end if yielded || result result else #{handle_save_failure} end end ", __FILE__, __LINE__ + 1 else super end end
Initializes class-level extensions for this machine
# File lib/state_machine/integrations/sequel.rb, line 327 def define_helpers load_plugins super end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/sequel.rb, line 354 def define_state_accessor define_helper :instance, " def validate(*) super machine = self.class.state_machine(#{name.inspect}) machine.invalidate(self, :state, :invalid) unless machine.states.match(self) end ", __FILE__, __LINE__ + 1 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, line 345 def define_state_initializer define_helper :instance, " def initialize_set(*) self.class.state_machines.initialize_states(self, :static => :force) { super } end ", __FILE__, __LINE__ + 1 end
Adds hooks into validation for automatically firing events
# File lib/state_machine/integrations/sequel.rb, line 408 def define_validation_hook define_helper :instance, " def around_validation(*) self.class.state_machines.transitions(self, :save, :after => false).perform { super } end ", __FILE__, __LINE__ + 1 end
Handles how save failures (due to invalid transitions) are raised
# File lib/state_machine/integrations/sequel.rb, line 395 def handle_save_failure 'raise_hook_failure(:before_transition) if raise_on_failure?(opts)' end
Loads the built-in inflector
# File lib/state_machine/integrations/sequel.rb, line 338 def load_inflector require 'sequel/extensions/inflector' end
Loads all of the Sequel plugins necessary to run
# File lib/state_machine/integrations/sequel.rb, line 333 def load_plugins owner_class.plugin(:hook_class_methods) end
Determines the model associated with the given dataset
# File lib/state_machine/integrations/sequel.rb, line 457 def model_from_dataset(dataset) dataset.model end
Gets the db default for the machine's attribute
# File lib/state_machine/integrations/sequel.rb, line 417 def owner_class_attribute_default if owner_class.db.table_exists?(owner_class.table_name) && column = owner_class.db_schema[attribute.to_sym] column[:default] end end
Uses the DB literal to match the default against the specified state
# File lib/state_machine/integrations/sequel.rb, line 424 def owner_class_attribute_default_matches?(state) owner_class.db.literal(state.value) == owner_class_attribute_default end
Generates the results for the given scope based on one or more states to filter by
# File lib/state_machine/integrations/sequel.rb, line 452 def run_scope(scope, dataset, states) super(scope, model_from_dataset(dataset).state_machine(name), dataset, states) 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, line 468 def transaction(object) result = nil object.db.transaction do raise ::Sequel::Error::Rollback unless result = yield end result end