module StateMachine::Integrations::DataMapper
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">
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 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.
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 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
Within DataMapper Hooks¶ ↑
DataMapper protects against the potential for system stack errors resulting from infinite loops by preventing records from being saved multiple times within save hooks. You need to be acutely aware of this when interacting with state_machine within save hooks. There are two things to keep in mind:
-
You cannot run a state_machine event during an `after :save/:create` hook.
-
If you need to run a state_machine event during a `before :save/:create/etc.` hook, then you have to force the machine's action to be skipped by passing `false` in as an argument to the event.
For example:
class Vehicle include DataMapper::Resource ... state_machine :initial => :parked do event :ignite do transition :parked => :idling end end # This will allow the event to transition without attempting to save a second time before :create { ignite(false) } # This will never work because DataMapper will refuse to save the # changes since we're still inside of a transaction # after :create { ignite } end
While the above will work, in reality you should typically just set the `state_event` attribute in `#initialize` to automatically transition an object on creation.
Transactions¶ ↑
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 include DataMapper::Resource ... state_machine :initial => :parked, :use_transactions => true 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 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.
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 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])
Note that states can also be referenced by the string version of their name:
Vehicle.with_state('parked')
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.
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 DataMapper, a save failure
will cause any records that get created in your callback to roll back.
Note that this is only a problem if the machine is
configured to use transactions. If it is, you can work around this issue
like so:
DataMapper.setup(:default, 'mysql://localhost/app') DataMapper.setup(:logs, 'mysql://localhost/app') class TransitionLog include DataMapper::Resource end class Vehicle < ActiveRecord::Base include DataMapper::Resource state_machine :use_transactions => true do after_failure do |transition| DataMapper.repository(:logs) do TransitionLog.create(:vehicle => vehicle, :transition => transition) end end ... end end
The failure callback creates TransitionLog
records using a
second connection to the database, allowing them to be saved without being
affected by rollbacks in the Vehicle
resource's
transaction.
Callback Order¶ ↑
Callbacks occur in the following order. Callbacks specific to state_machine are bolded. The remaining callbacks are part of ActiveRecord.
-
(-) save
-
(-) begin transaction (if enabled)
-
(1) before_transition
-
(2) before :valid?
-
(-) valid?
-
(3) after :valid?
-
(4) before :save
-
(-) save
-
(5) before :create
-
(-) create
-
(6) after :create
-
(7) after :save
-
(8) after_transition
-
(-) end transaction (if enabled)
Public Class Methods
# File lib/state_machine/integrations/data_mapper/versions.rb, line 5 def self.active? ::DataMapper::VERSION =~ /^0\.\d\./ || ::DataMapper::VERSION =~ /^0\.10\./ end
Classes that include DataMapper::Resource will automatically use the DataMapper integration.
# File lib/state_machine/integrations/data_mapper.rb, line 356 def self.matching_ancestors %w(DataMapper::Resource) end
Public Instance Methods
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 41 def define_action_helpers? super if action != :save || !supports_validations? end
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/data_mapper.rb, line 373 def errors_for(object) if object.errors.empty? 'Transition halted' else errors = [] object.errors.each_pair do |field_name, field_errors| field_errors.each {|error| errors << "#{field_name} #{error}"} end errors * ', ' end end
Adds a validation error to the given object
# File lib/state_machine/integrations/data_mapper.rb, line 367 def invalidate(object, attribute, message, values = []) object.errors.add(self.attribute(attribute), generate_message(message, values)) if supports_validations? end
Resets any errors previously added when invalidating the given object
# File lib/state_machine/integrations/data_mapper.rb, line 386 def reset(object) object.errors.clear if supports_validations? end
Protected Instance Methods
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 505 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 392 def after_initialize super load_observer_extensions end
Gets the property for this machine's attribute (if it exists)
# File lib/state_machine/integrations/data_mapper.rb, line 413 def attribute_property owner_class.properties.detect {|property| property.name == attribute} 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 486 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 492 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 447 def define_action_helpers if action_hook == :save define_helper :instance, " def save(*) result = self.class.state_machines.transitions(self, :save).perform { super } assert_save_successful(:save, result) result end def save!(*) result = self.class.state_machines.transitions(self, :save).perform { super } assert_save_successful(:save!, result) result end def save_self(*) self.class.state_machines.transitions(self, :save).perform { super } end ", __FILE__, __LINE__ + 1 define_validation_hook else super end end
Skips defining reader/writer methods since this is done automatically
# File lib/state_machine/integrations/data_mapper.rb, line 434 def define_state_accessor owner_class.property(attribute, String) unless attribute_property 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 425 def define_state_initializer define_helper :instance, " def initialize(*args) self.class.state_machines.initialize_states(self, :static => :force) { super } end ", __FILE__, __LINE__ + 1 end
Adds hooks into validation for automatically firing events
# File lib/state_machine/integrations/data_mapper.rb, line 474 def define_validation_hook if supports_validations? define_helper :instance, " def valid?(*) self.class.state_machines.transitions(self, :save, :after => false).perform { super } end ", __FILE__, __LINE__ + 1 end end
Loads extensions to DataMapper's Observers
# File lib/state_machine/integrations/data_mapper.rb, line 398 def load_observer_extensions require 'state_machine/integrations/data_mapper/observer' if ::DataMapper.const_defined?('Observer') end
Gets the db default for the machine's attribute
# File lib/state_machine/integrations/data_mapper.rb, line 408 def owner_class_attribute_default attribute_property && attribute_property.default end
Pluralizes the name using the built-in inflector
# File lib/state_machine/integrations/data_mapper.rb, line 418 def pluralize(word) ::DataMapper::Inflector.pluralize(word.to_s) end
Is validation support currently loaded?
# File lib/state_machine/integrations/data_mapper.rb, line 403 def supports_validations? @supports_validations ||= ::DataMapper.const_defined?('Validate') end
Runs a new database transaction, rolling back any changes if the yielded block fails (i.e. returns false).
# File lib/state_machine/integrations/data_mapper.rb, line 498 def transaction(object) object.class.transaction {|t| t.rollback unless yield} end