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.

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.

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)

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.

Attributes

defaults[R]

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 <= 13
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, line 229
def self.available?
  defined?(::Sequel::Model)
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, line 236
def self.matches?(klass)
  klass <= ::Sequel::Model
end

Public Instance Methods

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 254
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

# File lib/state_machine/integrations/sequel.rb, line 264
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 259
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

# File lib/state_machine/integrations/sequel.rb, line 242
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

action_hook() click to toggle source

Uses internal save hooks if using the :save action

# File lib/state_machine/integrations/sequel.rb, line 360
def action_hook
  action == :save ? :_save : super
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

# File lib/state_machine/integrations/sequel.rb, line 395
def add_callback(type, options, &block)
  options[:bind_to_object] = true
  options[:terminator] = @terminator ||= lambda {|result| result == false}
  super
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 376
def create_with_scope(name)
  lambda {|model, values| model.filter(:"#{owner_class.table_name}__#{attribute}" => 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 382
def create_without_scope(name)
  lambda {|model, values| model.filter(~{:"#{owner_class.table_name}__#{attribute}" => values})}
end
define_action_helpers() click to toggle source

Adds hooks into validation for automatically firing events. This is a bit more complicated than other integrations since Sequel doesn't provide an easy way to hook around validation calls

# File lib/state_machine/integrations/sequel.rb, line 311
def define_action_helpers
  super
  
  if action == :save
    define_helper :instance,               def valid?(*args)                yielded = false                result = self.class.state_machines.transitions(self, :save, :after => false).perform do                  yielded = true                  super                end                                if yielded || result                  result                else                  #{handle_validation_failure}                end              end, __FILE__, __LINE__ + 1
  end
end
define_action_hook() click to toggle source

Uses custom hooks for :save actions in order to preserve failure behavior within Sequel. This is a bit more complicated than other integrations since Sequel doesn't provide an easy way to hook around save calls.

# File lib/state_machine/integrations/sequel.rb, line 337
def define_action_hook
  if action == :save
    define_helper :instance,               def #{action_hook}(*)                yielded = false                result = self.class.state_machines.transitions(self, :save).perform do                  yielded = true                  super                end                                if yielded || result                  result                else                  #{handle_save_failure}                end              end, __FILE__, __LINE__ + 1
  else
    super
  end
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 300
def define_state_accessor
  name = self.name
  owner_class.validates_each(attribute) do |record, attr, value|
    machine = record.class.state_machine(name)
    machine.invalidate(record, :state, :invalid) unless machine.states.match(record)
  end
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 278
def define_state_initializer
  # Hooks in to attribute initialization to set the states *prior* to
  # the attributes being set
  define_helper :instance,             # Initializes dynamic states            def initialize(*)              super do |*args|                self.class.state_machines.initialize_states(self, :static => false)                changed_columns.clear                yield(*args) if block_given?              end            end                        # Initializes static states            def set(*)              self.class.state_machines.initialize_states(self, :dynamic => false) if values.empty?              super            end, __FILE__, __LINE__ + 1
end
handle_save_failure() click to toggle source

Handles how save failures are raised

# File lib/state_machine/integrations/sequel.rb, line 370
def handle_save_failure
  'raise_hook_failure(:save)'
end
handle_validation_failure() click to toggle source

Handles whether validation errors should be raised

# File lib/state_machine/integrations/sequel.rb, line 365
def handle_validation_failure
  'raise_on_failure?(args.first || {}) ? raise_hook_failure(:validation) : result'
end
load_inflector() click to toggle source

Loads the built-in inflector

# File lib/state_machine/integrations/sequel.rb, line 271
def load_inflector
  require 'sequel/extensions/inflector'
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 388
def transaction(object)
  object.db.transaction {raise ::Sequel::Error::Rollback unless yield}
end

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