Adds support for integrating state machines with DataMapper resources.
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.
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">
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 DataMapper, these automated events are run in the following order:
before validation - If validation feature loaded, run before callbacks and persist new states, then validate
before save - If validation feature was skipped/not loaded, run before callbacks and persist new states, then save
after save - Run after callbacks
For example,
vehicle = Vehicle.create # => #<Vehicle id=1 name=nil state="parked"> vehicle.state_event # => nil vehicle.state_event = 'invalid' vehicle.valid? # => false vehicle.errors # => #<DataMapper::Validate::ValidationErrors:0xb7a48b54 @errors={"state_event"=>["is invalid"]}> vehicle.state_event = 'ignite' vehicle.valid? # => true vehicle.save # => true 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 id=1 name=nil state="idling"> vehicle.state # => "idling"
This technique is always used for transitioning states when the save action (which is the default) is configured for the machine.
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 include DataMapper::Resource ... state_machine do ... end protected :state_event 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 include DataMapper::Resource ... state_machine do # Define private events here end protected :state_event= # Prevent access to events in the first machine # Allow both machines to share the same state state_machine :public_state, :attribute => :state do # Define public events here end end
By default, the use of transactions during an event transition is turned off to be consistent with DataMapper. This means that if changes are made to the database during a before callback, but the transition fails to complete, those changes will not be rolled back.
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 # => 1
To turn on transactions:
class Vehicle < ActiveRecord::Base state_machine :initial => :parked, :use_transactions => true do ... end end
If using the save action for the machine, this option will be ignored as the transaction behavior will depend on the save implementation within DataMapper.
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 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.
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])
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.
# File lib/state_machine/integrations/data_mapper/versions.rb, line 5 def self.active? ::DataMapper::VERSION =~ /^0\.9\./ end
Whether this integration is available. Only true if DataMapper::Resource is defined.
# File lib/state_machine/integrations/data_mapper.rb, line 254 def self.available? defined?(::DataMapper::Resource) end
Should this integration be used for state machines in the given class? Classes that include DataMapper::Resource will automatically use the DataMapper integration.
# File lib/state_machine/integrations/data_mapper.rb, line 261 def self.matches?(klass) klass <= ::DataMapper::Resource end
# File lib/state_machine/integrations/data_mapper/versions.rb, line 9 def action_hook action end
0.9.4 - 0.9.6 fails to run after callbacks when validations are enabled because of the way dm-validations integrates
# File lib/state_machine/integrations/data_mapper/versions.rb, line 45 def define_action_helpers? super if action != :save || !supports_validations? end
Adds a validation error to the given object
# File lib/state_machine/integrations/data_mapper.rb, line 285 def invalidate(object, attribute, message, values = []) object.errors.add(self.attribute(attribute), generate_message(message, values)) if supports_validations? end
# File lib/state_machine/integrations/data_mapper/versions.rb, line 13 def mark_dirty(object, value) object.original_values[self.attribute] = "#{value}-ignored" if object.original_values[self.attribute] == value end
# File lib/state_machine/integrations/data_mapper/versions.rb, line 23 def pluralize(word) ::Extlib::Inflection.pluralize(word.to_s) end
Resets any errors previously added when invalidating the given object
# File lib/state_machine/integrations/data_mapper.rb, line 290 def reset(object) object.errors.clear if supports_validations? end
Forces the change in state to be recognized regardless of whether the state value actually changed
# File lib/state_machine/integrations/data_mapper.rb, line 273 def write(object, attribute, value, *args) result = super if attribute == :state || attribute == :event && value value = read(object, :state) if attribute == :event mark_dirty(object, value) end result 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 DataMapper/Extlib callbacks
# File lib/state_machine/integrations/data_mapper.rb, line 378 def add_callback(type, options, &block) options[:bind_to_object] = true super end
Initializes class-level extensions and defaults for this machine
# File lib/state_machine/integrations/data_mapper.rb, line 296 def after_initialize load_observer_extensions end
Creates a scope for finding records with a particular state or states for the attribute
# File lib/state_machine/integrations/data_mapper.rb, line 359 def create_with_scope(name) lambda {|resource, values| resource.all(attribute => values)} end
Creates a scope for finding records without a particular state or states for the attribute
# File lib/state_machine/integrations/data_mapper.rb, line 365 def create_without_scope(name) lambda {|resource, values| resource.all(attribute.to_sym.not => values)} end
Adds hooks into validation for automatically firing events
# File lib/state_machine/integrations/data_mapper.rb, line 340 def define_action_helpers super if action == :save && supports_validations? define_helper :instance, def valid?(*) self.class.state_machines.transitions(self, :save, :after => false).perform { super } end, __FILE__, __LINE__ + 1 end end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/data_mapper.rb, line 327 def define_state_accessor owner_class.property(attribute, String) unless owner_class.properties.detect {|property| property.name == attribute} if supports_validations? name = self.name owner_class.validates_with_block(attribute) do machine = self.class.state_machine(name) machine.states.match(self) ? true : [false, machine.generate_message(:invalid)] end end 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
# File lib/state_machine/integrations/data_mapper.rb, line 318 def define_state_initializer define_helper :instance, def initialize(*args) self.class.state_machines.initialize_states(self) { super } end, __FILE__, __LINE__ + 1 end
Loads extensions to DataMapper's Observers
# File lib/state_machine/integrations/data_mapper.rb, line 301 def load_observer_extensions require 'state_machine/integrations/data_mapper/observer' if ::DataMapper.const_defined?('Observer') end
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