require 'singleton' require 'active_model/observer_array' require 'active_support/core_ext/module/aliasing' require 'active_support/core_ext/module/remove_method' require 'active_support/core_ext/string/inflections' require 'active_support/core_ext/enumerable' require 'active_support/descendants_tracker' module ActiveModel module Observing extend ActiveSupport::Concern included do extend ActiveSupport::DescendantsTracker end module ClassMethods # == Active Model Observers Activation # # Activates the observers assigned. Examples: # # class ORM # include ActiveModel::Observing # end # # # Calls PersonObserver.instance # ORM.observers = :person_observer # # # Calls Cacher.instance and GarbageCollector.instance # ORM.observers = :cacher, :garbage_collector # # # Same as above, just using explicit class references # ORM.observers = Cacher, GarbageCollector # # Note: Setting this does not instantiate the observers yet. # +instantiate_observers+ is called during startup, and before # each development request. def observers=(*values) observers.replace(values.flatten) end # Gets an array of observers observing this model. # The array also provides +enable+ and +disable+ methods # that allow you to selectively enable and disable observers. # (see ActiveModel::ObserverArray.enable and # ActiveModel::ObserverArray.disable for more on this) def observers @observers ||= ObserverArray.new(self) end # Gets the current observer instances. def observer_instances @observer_instances ||= [] end # Instantiate the global observers. def instantiate_observers observers.each { |o| instantiate_observer(o) } end # Add a new observer to the pool. # The new observer needs to respond to 'update', otherwise it # raises an +ArgumentError+ exception. def add_observer(observer) unless observer.respond_to? :update raise ArgumentError, "observer needs to respond to `update'" end observer_instances << observer end # Notify list of observers of a change. def notify_observers(*arg) observer_instances.each { |observer| observer.update(*arg) } end # Total number of observers. def count_observers observer_instances.size end protected def instantiate_observer(observer) #:nodoc: # string/symbol if observer.respond_to?(:to_sym) observer.to_s.camelize.constantize.instance elsif observer.respond_to?(:instance) observer.instance else raise ArgumentError, "#{observer} must be a lowercase, underscored class name (or an " + "instance of the class itself) responding to the instance " + "method. Example: Person.observers = :big_brother # calls " + "BigBrother.instance" end end # Notify observers when the observed class is subclassed. def inherited(subclass) super notify_observers :observed_class_inherited, subclass end end private # Fires notifications to model's observers # # def save # notify_observers(:before_save) # ... # notify_observers(:after_save) # end def notify_observers(method) self.class.notify_observers(method, self) end end # == Active Model Observers # # Observer classes respond to life cycle callbacks to implement trigger-like # behavior outside the original class. This is a great way to reduce the # clutter that normally comes when the model class is burdened with # functionality that doesn't pertain to the core responsibility of the # class. Example: # # class CommentObserver < ActiveModel::Observer # def after_save(comment) # Notifications.comment("admin@do.com", "New comment was posted", comment).deliver # end # end # # This Observer sends an email when a Comment#save is finished. # # class ContactObserver < ActiveModel::Observer # def after_create(contact) # contact.logger.info('New contact added!') # end # # def after_destroy(contact) # contact.logger.warn("Contact with an id of #{contact.id} was destroyed!") # end # end # # This Observer uses logger to log when specific callbacks are triggered. # # == Observing a class that can't be inferred # # Observers will by default be mapped to the class with which they share a # name. So CommentObserver will be tied to observing Comment, ProductManagerObserver # to ProductManager, and so on. If you want to name your observer differently than # the class you're interested in observing, you can use the Observer.observe # class method which takes either the concrete class (Product) or a symbol for that # class (:product): # # class AuditObserver < ActiveModel::Observer # observe :account # # def after_update(account) # AuditTrail.new(account, "UPDATED") # end # end # # If the audit observer needs to watch more than one kind of object, this can be # specified with multiple arguments: # # class AuditObserver < ActiveModel::Observer # observe :account, :balance # # def after_update(record) # AuditTrail.new(record, "UPDATED") # end # end # # The AuditObserver will now act on both updates to Account and Balance by treating # them both as records. # # If you're using an Observer in a Rails application with Active Record, be sure to # read about the necessary configuration in the documentation for # ActiveRecord::Observer. # class Observer include Singleton extend ActiveSupport::DescendantsTracker class << self # Attaches the observer to the supplied model classes. def observe(*models) models.flatten! models.collect! { |model| model.respond_to?(:to_sym) ? model.to_s.camelize.constantize : model } redefine_method(:observed_classes) { models } end # Returns an array of Classes to observe. # # You can override this instead of using the +observe+ helper. # # class AuditObserver < ActiveModel::Observer # def self.observed_classes # [Account, Balance] # end # end def observed_classes Array(observed_class) end # The class observed by default is inferred from the observer's class name: # assert_equal Person, PersonObserver.observed_class def observed_class if observed_class_name = name[/(.*)Observer/, 1] observed_class_name.constantize else nil end end end # Start observing the declared classes and their subclasses. def initialize observed_classes.each { |klass| add_observer!(klass) } end def observed_classes #:nodoc: self.class.observed_classes end # Send observed_method(object) if the method exists and # the observer is enabled for the given object's class. def update(observed_method, object, &block) #:nodoc: return unless respond_to?(observed_method) return if disabled_for?(object) send(observed_method, object, &block) end # Special method sent by the observed class when it is inherited. # Passes the new subclass. def observed_class_inherited(subclass) #:nodoc: self.class.observe(observed_classes + [subclass]) add_observer!(subclass) end protected def add_observer!(klass) #:nodoc: klass.add_observer(self) end def disabled_for?(object) klass = object.class return false unless klass.respond_to?(:observers) klass.observers.disabled_for?(self) end end end