require 'singleton' module ActiveRecord module Observing # :nodoc: def self.append_features(base) super base.extend(ClassMethods) end module ClassMethods # Activates the observers assigned. Examples: # # # Calls PersonObserver.instance # ActiveRecord::Base.observers = :person_observer # # # Calls Cacher.instance and GarbageCollector.instance # ActiveRecord::Base.observers = :cacher, :garbage_collector # # # Same as above, just using explicit class references # ActiveRecord::Base.observers = Cacher, GarbageCollector def observers=(*observers) observers = [ observers ].flatten.each do |observer| observer.is_a?(Symbol) ? observer.to_s.camelize.constantize.instance : observer.instance end end end end # Observer classes respond to lifecycle 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 < ActiveRecord::Observer # def after_save(comment) # Notifications.deliver_comment("admin@do.com", "New comment was posted", comment) # end # end # # This Observer sends an email when a Comment#save is finished. # # class ContactObserver < ActiveRecord::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: # # class AuditObserver < ActiveRecord::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 < ActiveRecord::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. # # == Available callback methods # # The observer can implement callback methods for each of the methods described in the Callbacks module. # # == Storing Observers in Rails # # If you're using Active Record within Rails, observer classes are usually stored in app/models with the # naming convention of app/models/audit_observer.rb. # # == Configuration # # In order to activate an observer, list it in the config.active_record.observers configuration setting in your # config/environment.rb file. # # config.active_record.observers = :comment_observer, :signup_observer # # Observers will not be invoked unless you define these in your application configuration. # class Observer include Singleton # Observer subclasses should be reloaded by the dispatcher in Rails # when Dependencies.mechanism = :load. include Reloadable::Subclasses # Attaches the observer to the supplied model classes. def self.observe(*models) define_method(:observed_class) { models } end def initialize observed_classes = [ observed_class ].flatten observed_subclasses_class = observed_classes.collect {|c| c.send(:subclasses) }.flatten! (observed_classes + observed_subclasses_class).each do |klass| klass.add_observer(self) klass.send(:define_method, :after_find) unless klass.respond_to?(:after_find) end end def update(callback_method, object) #:nodoc: send(callback_method, object) if respond_to?(callback_method) end private def observed_class if self.class.respond_to? "observed_class" self.class.observed_class else Object.const_get(infer_observed_class_name) end end def infer_observed_class_name self.class.name.scan(/(.*)Observer/)[0][0] end end end