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require 'singleton'
module ActiveRecord
module Observing # :nodoc:
def self.included(base)
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 <tt>config.active_record.observers</tt> configuration setting in your
# <tt>config/environment.rb</tt> 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
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