198 lines
6.9 KiB
Ruby
198 lines
6.9 KiB
Ruby
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require 'singleton'
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require 'set'
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module ActiveRecord
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module Observing # :nodoc:
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def self.included(base)
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base.extend ClassMethods
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end
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module ClassMethods
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# Activates the observers assigned. Examples:
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#
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# # Calls PersonObserver.instance
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# ActiveRecord::Base.observers = :person_observer
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#
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# # Calls Cacher.instance and GarbageCollector.instance
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# ActiveRecord::Base.observers = :cacher, :garbage_collector
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#
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# # Same as above, just using explicit class references
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# ActiveRecord::Base.observers = Cacher, GarbageCollector
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#
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# Note: Setting this does not instantiate the observers yet. +instantiate_observers+ is
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# called during startup, and before each development request.
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def observers=(*observers)
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@observers = observers.flatten
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end
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# Gets the current observers.
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def observers
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@observers ||= []
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end
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# Instantiate the global Active Record observers.
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def instantiate_observers
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return if @observers.blank?
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@observers.each do |observer|
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if observer.respond_to?(:to_sym) # Symbol or String
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observer.to_s.camelize.constantize.instance
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elsif observer.respond_to?(:instance)
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observer.instance
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else
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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"
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end
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end
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end
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protected
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# Notify observers when the observed class is subclassed.
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def inherited(subclass)
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super
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changed
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notify_observers :observed_class_inherited, subclass
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end
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end
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end
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# Observer classes respond to lifecycle callbacks to implement trigger-like
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# behavior outside the original class. This is a great way to reduce the
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# clutter that normally comes when the model class is burdened with
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# functionality that doesn't pertain to the core responsibility of the
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# class. Example:
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#
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# class CommentObserver < ActiveRecord::Observer
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# def after_save(comment)
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# Notifications.deliver_comment("admin@do.com", "New comment was posted", comment)
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# end
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# end
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#
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# This Observer sends an email when a Comment#save is finished.
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#
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# class ContactObserver < ActiveRecord::Observer
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# def after_create(contact)
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# contact.logger.info('New contact added!')
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# end
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#
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# def after_destroy(contact)
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# contact.logger.warn("Contact with an id of #{contact.id} was destroyed!")
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# end
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# end
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#
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# This Observer uses logger to log when specific callbacks are triggered.
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#
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# == Observing a class that can't be inferred
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#
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# Observers will by default be mapped to the class with which they share a name. So CommentObserver will
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# be tied to observing Comment, ProductManagerObserver to ProductManager, and so on. If you want to name your observer
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# differently than the class you're interested in observing, you can use the Observer.observe class method which takes
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# either the concrete class (Product) or a symbol for that class (:product):
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#
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# class AuditObserver < ActiveRecord::Observer
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# observe :account
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#
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# def after_update(account)
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# AuditTrail.new(account, "UPDATED")
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# end
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# end
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#
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# If the audit observer needs to watch more than one kind of object, this can be specified with multiple arguments:
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#
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# class AuditObserver < ActiveRecord::Observer
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# observe :account, :balance
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#
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# def after_update(record)
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# AuditTrail.new(record, "UPDATED")
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# end
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# end
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#
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# The AuditObserver will now act on both updates to Account and Balance by treating them both as records.
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#
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# == Available callback methods
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#
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# The observer can implement callback methods for each of the methods described in the Callbacks module.
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#
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# == Storing Observers in Rails
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#
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# If you're using Active Record within Rails, observer classes are usually stored in app/models with the
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# naming convention of app/models/audit_observer.rb.
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#
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# == Configuration
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#
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# In order to activate an observer, list it in the <tt>config.active_record.observers</tt> configuration setting in your
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# <tt>config/environment.rb</tt> file.
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#
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# config.active_record.observers = :comment_observer, :signup_observer
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#
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# Observers will not be invoked unless you define these in your application configuration.
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#
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# == Loading
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#
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# Observers register themselves in the model class they observe, since it is the class that
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# notifies them of events when they occur. As a side-effect, when an observer is loaded its
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# corresponding model class is loaded.
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#
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# Up to (and including) Rails 2.0.2 observers were instantiated between plugins and
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# application initializers. Now observers are loaded after application initializers,
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# so observed models can make use of extensions.
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#
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# If by any chance you are using observed models in the initialization you can still
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# load their observers by calling <tt>ModelObserver.instance</tt> before. Observers are
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# singletons and that call instantiates and registers them.
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#
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class Observer
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include Singleton
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class << self
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# Attaches the observer to the supplied model classes.
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def observe(*models)
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models.flatten!
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models.collect! { |model| model.is_a?(Symbol) ? model.to_s.camelize.constantize : model }
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define_method(:observed_classes) { Set.new(models) }
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end
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# The class observed by default is inferred from the observer's class name:
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# assert_equal Person, PersonObserver.observed_class
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def observed_class
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if observed_class_name = name[/(.*)Observer/, 1]
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observed_class_name.constantize
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else
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nil
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end
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end
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end
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# Start observing the declared classes and their subclasses.
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def initialize
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Set.new(observed_classes + observed_subclasses).each { |klass| add_observer! klass }
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end
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# Send observed_method(object) if the method exists.
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def update(observed_method, object) #:nodoc:
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send(observed_method, object) if respond_to?(observed_method)
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end
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# Special method sent by the observed class when it is inherited.
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# Passes the new subclass.
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def observed_class_inherited(subclass) #:nodoc:
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self.class.observe(observed_classes + [subclass])
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add_observer!(subclass)
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end
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protected
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def observed_classes
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Set.new([self.class.observed_class].compact.flatten)
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end
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def observed_subclasses
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observed_classes.sum([]) { |klass| klass.send(:subclasses) }
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end
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def add_observer!(klass)
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klass.add_observer(self)
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if respond_to?(:after_find) && !klass.method_defined?(:after_find)
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klass.class_eval 'def after_find() end'
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end
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end
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end
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end
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