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

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

defaults[R]

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
available?() click to toggle source

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
matches?(klass) click to toggle source

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

define_action_hook() click to toggle source
Calls superclass method
   # 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
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_save_failure() click to toggle source
    # File lib/state_machine/integrations/sequel/versions.rb
100 def handle_save_failure
101   'save_failure(:save)'
102 end
handle_validation_failure() click to toggle source
   # File lib/state_machine/integrations/sequel/versions.rb
96 def handle_validation_failure
97   'raise_on_save_failure ? save_failure(:validation) : result'
98 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

action_hook() click to toggle source

Uses internal save hooks if using the :save action

Calls superclass method
    # File lib/state_machine/integrations/sequel.rb
379 def action_hook
380   action == :save ? :around_save : super
381 end
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
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
attribute_column() click to toggle source

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
create_scope(name, scope) click to toggle source

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
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
385 def create_with_scope(name)
386   create_scope(name, lambda {|dataset, values| dataset.filter(attribute_column => values)})
387 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
391 def create_without_scope(name)
392   create_scope(name, lambda {|dataset, values| dataset.exclude(attribute_column => values)})
393 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
364 def define_action_helpers
365   super
366   define_validation_hook if action == :save
367 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
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
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
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
define_validation_hook() click to toggle source

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
load_inflector() click to toggle source

Loads the built-in inflector

    # File lib/state_machine/integrations/sequel.rb
339 def load_inflector
340   require 'sequel/extensions/inflector'
341 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(:validation_class_methods)
335   owner_class.plugin(:hook_class_methods)
336 end
model_from_dataset(dataset) click to toggle source

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
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
407 def run_scope(scope, dataset, states)
408   super(scope, model_from_dataset(dataset).state_machine(name), dataset, states)
409 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
423 def transaction(object)
424   object.db.transaction {raise ::Sequel::Error::Rollback unless yield}
425 end