Module: StateMachine::Integrations::DataMapper

Defined in:
lib/state_machine/integrations/data_mapper.rb,
lib/state_machine/integrations/data_mapper/observer.rb

Overview

Adds support for integrating state machines with DataMapper resources.

Examples

Below is an example of a simple state machine defined within a DataMapper resource:

class Vehicle
include DataMapper::Resource

property :id, Serial
property :name, String
property :state, String

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 saved as well.

For example,

vehicle = Vehicle.create          # => #<Vehicle id=1 name=nil state="parked">
vehicle.name = 'Ford Explorer'
vehicle.ignite                    # => true
vehicle.reload                    # => #<Vehicle id=1 name="Ford Explorer" state="idling">

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
include DataMapper::Resource

property :id, Serial
property :content, String
end

Vehicle.state_machine do
before_transition do |transition|
  Message.create(:content => transition.inspect)
  throw :halt
end
end

vehicle = Vehicle.create      # => #<Vehicle id=1 name=nil state="parked">
vehicle.ignite                # => false
Message.all.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.

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 id=1 name=nil state="idling">
vehicle.ignite                                # => false
vehicle.errors.full_messages                  # => ["cannot be transitioned via :ignite from :idling"]

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
include DataMapper::Resource

property :id, Serial
property :state, String

class << self
  def with_states(*states)
    all(:state => states.flatten)
  end
  alias_method :with_state, :with_states
  
  def without_states(*states)
    all(:state.not => states.flatten)
  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 DataMapper, they can be chained like so:

Vehicle.with_state(:parked).all(:order => [:id.desc])

Callbacks / Observers

All before/after transition callbacks defined for DataMapper resources behave in the same way that other DataMapper 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
include DataMapper::Resource

property :id, Serial
property :state, String

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.

In addition to support for DataMapper-like hooks, there is additional support for DataMapper observers. See StateMachine::Integrations::DataMapper::Observer for more information.

Defined Under Namespace

Modules: Observer

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.extended(base) ⇒ Object

Loads additional files specific to DataMapper



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# File 'lib/state_machine/integrations/data_mapper.rb', line 175

def self.extended(base) #:nodoc:
  require 'state_machine/integrations/data_mapper/observer' if ::DataMapper.const_defined?('Observer')
end

.matches?(klass) ⇒ Boolean

Should this integration be used for state machines in the given class? Classes that include DataMapper::Resource will automatically use the DataMapper integration.

Returns:

  • (Boolean) 


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# File 'lib/state_machine/integrations/data_mapper.rb', line 170

def self.matches?(klass)
  defined?(::DataMapper::Resource) && klass <= ::DataMapper::Resource
end

Instance Method Details

#invalidate(object, event) ⇒ Object

Adds a validation error to the given object after failing to fire a specific event



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# File 'lib/state_machine/integrations/data_mapper.rb', line 181

def invalidate(object, event)
  object.errors.add(attribute, invalid_message(object, event)) if object.respond_to?(:errors)
end

#reset(object) ⇒ Object

Resets an errors previously added when invalidating the given object



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# File 'lib/state_machine/integrations/data_mapper.rb', line 186

def reset(object)
  object.errors.clear
end

#within_transaction(object) ⇒ Object

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



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# File 'lib/state_machine/integrations/data_mapper.rb', line 192

def within_transaction(object)
  object.class.transaction {|t| t.rollback unless yield}
end