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, line 5
def self.active?
  !defined?(::Sequel::MAJOR) || ::Sequel::MAJOR == 2 || ::Sequel::MAJOR == 3 && ::Sequel::MINOR <= 23
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, line 286
def self.matching_ancestors
  %w(Sequel::Model)
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, line 310
def errors_for(object)
  object.errors.empty? ? 'Transition halted' : object.errors.full_messages * ', '
end
handle_validation_failure() click to toggle source
# File lib/state_machine/integrations/sequel/versions.rb, line 51
def handle_validation_failure
  'raise_on_save_failure ? save_failure(:validation) : result'
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, line 304
def invalidate(object, attribute, message, values = [])
  object.errors.add(self.attribute(attribute), generate_message(message, values))
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, line 320
def pluralize(word)
  load_inflector
  super
end
reset(object) click to toggle source

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
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, 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

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, line 479
def add_callback(type, options, &block)
  options[:bind_to_object] = true
  options[:terminator] = @terminator ||= lambda {|result| result == false}
  super
end
around_save(object) { || ... } click to toggle source

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
attribute_column() click to toggle source

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
create_scope(name, scope) click to toggle source

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
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, line 430
def create_with_scope(name)
  create_scope(name, lambda {|dataset, values| dataset.filter(attribute_column => values)})
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, line 436
def create_without_scope(name)
  create_scope(name, lambda {|dataset, values| dataset.exclude(attribute_column => values)})
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, line 365
def define_action_helpers
  super
  define_validation_hook if action == :save
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, 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
define_helpers() click to toggle source

Initializes class-level extensions for this machine

Calls superclass method
# File lib/state_machine/integrations/sequel.rb, line 327
def define_helpers
  load_plugins
  super
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, 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
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, 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
define_validation_hook() click to toggle source

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
handle_save_failure() click to toggle source

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
load_inflector() click to toggle source

Loads the built-in inflector

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

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
model_from_dataset(dataset) click to toggle source

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
owner_class_attribute_default() click to toggle source

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
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, line 424
def owner_class_attribute_default_matches?(state)
  owner_class.db.literal(state.value) == owner_class_attribute_default
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, line 452
def run_scope(scope, dataset, states)
  super(scope, model_from_dataset(dataset).state_machine(name), dataset, states)
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, line 468
def transaction(object)
  result = nil
  object.db.transaction do
    raise ::Sequel::Error::Rollback unless result = yield
  end
  result
end