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# encoding: utf-8
module Mongoid
# 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. Mongoid's observers work similar to ActiveRecord's. Example:
#
# class CommentObserver < Mongoid::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 < Mongoid::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 < Mongoid::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 < Mongoid::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
#
# * after_initialize
# * before_validation
# * after_validation
# * before_create
# * around_create
# * after_create
# * before_update
# * around_update
# * after_update
# * before_upsert
# * around_upsert
# * after_upsert
# * before_save
# * around_save
# * after_save
# * before_destroy
# * around_destroy
# * after_destroy
#
# == Storing Observers in Rails
#
# If you're using Mongoid 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.mongoid.observers+
# configuration setting in your +config/application.rb+ file.
#
# config.mongoid.observers = :comment_observer, :signup_observer
#
# Observers will not be invoked unless you define them in your
# application configuration.
#
# == Loading
#
# Observers register themselves with the model class that they observe,
# since it is the class that notifies them of events when they occur.
# As a side-effect, when an observer is loaded, its corresponding model
# class is loaded.
#
# Observers are loaded after the application initializers, so that
# observed models can make use of extensions. If by any chance you are
# using observed models in the initialization, you can
# still load their observers by calling +ModelObserver.instance+ before.
# Observers are singletons and that call instantiates and registers them.
class Observer < ActiveModel::Observer
private
# Adds the specified observer to the class.
#
# @example Add the observer.
# observer.add_observer!(Document)
#
# @param [ Class ] klass The child observer to add.
#
# @since 2.0.0.rc.8
def add_observer!(klass)
super and define_callbacks(klass)
end
# Defines all the callbacks for each observer of the model.
#
# @example Define all the callbacks.
# observer.define_callbacks(Document)
#
# @param [ Class ] klass The model to define them on.
#
# @since 2.0.0.rc.8
def define_callbacks(klass)
observer = self
observer_name = observer.class.name.underscore.gsub('/', '__')
Mongoid::Callbacks.observables.each do |callback|
next unless respond_to?(callback)
callback_meth = :"_notify_#{observer_name}_for_#{callback}"
unless klass.respond_to?(callback_meth)
klass.send(:define_method, callback_meth) do |&block|
if value = observer.update(callback, self, &block)
value
else
block.call if block
end
end
klass.send(callback, callback_meth)
end
end
self
end
# Are the observers disabled for the object?
#
# @api private
#
# @example If the observer disabled?
# Observer.disabled_for(band)
#
# @param [ Document ] object The model instance.
#
# @return [ true, false ] If the observer is disabled.
def disabled_for?(object)
klass = object.class
return false unless klass.respond_to?(:observers)
klass.observers.disabled_for?(self) || Mongoid.observers.disabled_for?(self)
end
end
end
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