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:

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.

Public Class Methods

active?() click to toggle source
  # 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
matching_ancestors() click to toggle source

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

errors_for(object) click to toggle source

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
handle_validation_failure() click to toggle source
   # File lib/state_machine/integrations/sequel/versions.rb
51 def handle_validation_failure
52   'raise_on_save_failure ? save_failure(:validation) : result'
53 end
invalidate(object, attribute, message, values = []) click to toggle source

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
pluralize(word) click to toggle source

Pluralizes the name using the built-in inflector

Calls superclass method
    # File lib/state_machine/integrations/sequel.rb
320 def pluralize(word)
321   load_inflector
322   super
323 end
reset(object) click to toggle source

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
write(object, attribute, value, *args) click to toggle source

Forces the change in state to be recognized regardless of whether the state value actually changed

Calls superclass method
    # 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

add_callback(type, options, &block) click to toggle source

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

Calls superclass method
    # 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
around_save(object) { || ... } click to toggle source

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
attribute_column() click to toggle source

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
create_scope(name, scope) click to toggle source

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
create_with_scope(name) click to toggle source

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
create_without_scope(name) click to toggle source

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
define_action_helpers() click to toggle source

Defines validation hooks if the machine’s action is to save the model

Calls superclass method
    # File lib/state_machine/integrations/sequel.rb
365 def define_action_helpers
366   super
367   define_validation_hook if action == :save
368 end
define_action_hook() click to toggle source

Uses around callbacks to run state events if using the :save hook

Calls superclass method
    # 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
define_helpers() click to toggle source

Initializes class-level extensions for this machine

Calls superclass method
    # File lib/state_machine/integrations/sequel.rb
327 def define_helpers
328   load_plugins
329   super
330 end
define_state_accessor() click to toggle source

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
define_state_initializer() click to toggle source

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
define_validation_hook() click to toggle source

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
handle_save_failure() click to toggle source

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
load_inflector() click to toggle source

Loads the built-in inflector

    # File lib/state_machine/integrations/sequel.rb
338 def load_inflector
339   require 'sequel/extensions/inflector'
340 end
load_plugins() click to toggle source

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
model_from_dataset(dataset) click to toggle source

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
owner_class_attribute_default() click to toggle source

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
owner_class_attribute_default_matches?(state) click to toggle source

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
run_scope(scope, dataset, states) click to toggle source

Generates the results for the given scope based on one or more states to filter by

Calls superclass method
    # 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
transaction(object) { || ... } click to toggle source

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