Module StateMachine::Integrations::Sequel
In: lib/state_machine/integrations/sequel.rb
lib/state_machine/integrations/sequel/versions.rb

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.

Methods

Included Modules

Base

Attributes

defaults  [R] 

Public Class methods

[Source]

     # File lib/state_machine/integrations/sequel/versions.rb, line 109
109:         def self.active?
110:           defined?(::Sequel::MAJOR) && ::Sequel::MAJOR == 3 && ::Sequel::MINOR >= 14 && ::Sequel::MINOR <= 23
111:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 75
75:         def self.active?
76:           !defined?(::Sequel::MAJOR) || ::Sequel::MAJOR == 2 && ::Sequel::MINOR <= 11
77:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 95
95:         def self.active?
96:           !defined?(::Sequel::MAJOR) || ::Sequel::MAJOR == 2 || ::Sequel::MAJOR == 3 && ::Sequel::MINOR <= 13
97:         end

[Source]

   # File lib/state_machine/integrations/sequel/versions.rb, line 5
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.

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 279
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.

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 286
286:       def self.matches?(klass)
287:         klass <= ::Sequel::Model
288:       end

Public Instance methods

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 69
69:         def action_hook
70:           action == :save ? :_save : super
71:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 85
85:         def action_hook
86:           action == :save ? :save : super
87:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 46
46:         def define_action_hook
47:           if action == :save
48:             define_helper :instance, "def \#{action_hook}(*)\nyielded = false\nresult = self.class.state_machines.transitions(self, :save).perform do\nyielded = true\nsuper\nend\n\nif yielded || result\nresult\nelse\n\#{handle_save_failure}\nend\nend\n", __FILE__, __LINE__ + 1
49:           else
50:             super
51:           end
52:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 9
 9:         def define_state_initializer
10:           define_helper :instance, "def initialize(*)\nsuper do |*args|\nself.class.state_machines.initialize_states(self, :static => false)\nchanged_columns.clear\nyield(*args) if block_given?\nend\nend\n\ndef set(*)\nself.class.state_machines.initialize_states(self, :dynamic => false) if values.empty?\nsuper\nend\n", __FILE__, __LINE__ + 1
11:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 27
27:         def define_validation_hook
28:           define_helper :instance, "def valid?(*args)\nyielded = false\nresult = self.class.state_machines.transitions(self, :save, :after => false).perform do\nyielded = true\nsuper\nend\n\nif yielded || result\nresult\nelse\n\#{handle_validation_failure}\nend\nend\n", __FILE__, __LINE__ + 1
29:         end

Describes the current validation errors on the given object. If none are specific, then the default error is interpeted as a "halt".

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 310
310:       def errors_for(object)
311:         object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', '
312:       end

[Source]

     # File lib/state_machine/integrations/sequel/versions.rb, line 103
103:         def handle_save_failure
104:           'save_failure(:save)'
105:         end

[Source]

     # File lib/state_machine/integrations/sequel/versions.rb, line 117
117:         def handle_save_failure
118:           'raise_hook_failure(:save)'
119:         end

[Source]

     # File lib/state_machine/integrations/sequel/versions.rb, line 99
 99:         def handle_validation_failure
100:           'raise_on_save_failure ? save_failure(:validation) : result'
101:         end

[Source]

     # File lib/state_machine/integrations/sequel/versions.rb, line 113
113:         def handle_validation_failure
114:           'raise_on_failure?(args.first || {}) ? raise_hook_failure(:validation) : result'
115:         end

Adds a validation error to the given object

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 304
304:       def invalidate(object, attribute, message, values = [])
305:         object.errors.add(self.attribute(attribute), generate_message(message, values))
306:       end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 82
82:         def load_inflector
83:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 79
79:         def load_plugins
80:         end

[Source]

    # File lib/state_machine/integrations/sequel/versions.rb, line 89
89:         def model_from_dataset(dataset)
90:           dataset.model_classes[nil]
91:         end

Pluralizes the name using the built-in inflector

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 320
320:       def pluralize(word)
321:         load_inflector
322:         super
323:       end

Resets any errors previously added when invalidating the given object

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 315
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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 292
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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 381
381:         def action_hook
382:           action == :save ? :around_save : super
383:         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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 432
432:         def add_callback(type, options, &block)
433:           options[:bind_to_object] = true
434:           options[:terminator] = @terminator ||= lambda {|result| result == false}
435:           super
436:         end

Generates the fully-qualifed column name for this machine‘s attribute

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 419
419:         def attribute_column
420:           ::Sequel::SQL::QualifiedIdentifier.new(owner_class.table_name, attribute)
421:         end

Creates a new named scope with the given name

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 398
398:         def create_scope(name, scope)
399:           machine = self
400:           owner_class.def_dataset_method(name) do |*states|
401:             machine.send(:run_scope, scope, self, states)
402:           end
403:           
404:           false
405:         end

Creates a scope for finding records with a particular state or states for the attribute

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 387
387:         def create_with_scope(name)
388:           create_scope(name, lambda {|dataset, values| dataset.filter(attribute_column => values)})
389:         end

Creates a scope for finding records without a particular state or states for the attribute

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 393
393:         def create_without_scope(name)
394:           create_scope(name, lambda {|dataset, values| dataset.exclude(attribute_column => values)})
395:         end

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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 365
365:         def define_action_helpers
366:           super
367:           define_validation_hook if action == :save
368:         end

Initializes class-level extensions for this machine

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 327
327:         def define_helpers
328:           load_plugins
329:           super
330:         end

Skips defining reader/writer methods since this is done automatically

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 356
356:         def define_state_accessor
357:           name = self.name
358:           owner_class.validates_each(attribute) do |record, attr, value|
359:             machine = record.class.state_machine(name)
360:             machine.invalidate(record, :state, :invalid) unless machine.states.match(record)
361:           end
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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 346
346:         def define_state_initializer
347:           define_helper :instance, "def initialize_set(*)\nself.class.state_machines.initialize_states(self) { super }\nend\n", __FILE__, __LINE__ + 1
348:         end

Adds hooks into validation for automatically firing events

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 371
371:         def define_validation_hook
372:           define_helper :instance, "def around_validation(*)\nself.class.state_machines.transitions(self, :save, :after => false).perform { super }\nend\n", __FILE__, __LINE__ + 1
373:         end

Loads the built-in inflector

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 339
339:         def load_inflector
340:           require 'sequel/extensions/inflector'
341:         end

Loads all of the Sequel plugins necessary to run

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 333
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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 414
414:         def model_from_dataset(dataset)
415:           dataset.model
416:         end

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

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 409
409:         def run_scope(scope, dataset, states)
410:           super(scope, model_from_dataset(dataset).state_machine(name), dataset, states)
411:         end

Runs a new database transaction, rolling back any changes if the yielded block fails (i.e. returns false).

[Source]

     # File lib/state_machine/integrations/sequel.rb, line 425
425:         def transaction(object)
426:           object.db.transaction {raise ::Sequel::Error::Rollback unless yield}
427:         end

[Validate]