1 files changed, 36 insertions, 9 deletions

diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index ef36f80bec..4682ae07ef 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -1,13 +1,20 @@
 require 'singleton'
+require 'active_model/observer_array'
 require 'active_support/core_ext/array/wrap'
 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
       #
@@ -30,12 +37,16 @@ module ActiveModel
       # +instantiate_observers+ is called during startup, and before
       # each development request.
       def observers=(*values)
-        @observers = values.flatten
+        observers.replace(values.flatten)
       end
 
-      # Gets the current observers.
+      # 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 <tt>ActiveModel::ObserverArray.enable</tt> and
+      # <tt>ActiveModel::ObserverArray.disable</tt> for more on this)
       def observers
-        @observers ||= []
+        @observers ||= ObserverArray.new(self)
       end
 
       # Gets the current observer instances.
@@ -43,12 +54,14 @@ module ActiveModel
         @observer_instances ||= []
       end
 
-      # Instantiate the global Active Record observers.
+      # 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'"
@@ -76,7 +89,11 @@ module ActiveModel
           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"
+            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
 
@@ -133,8 +150,8 @@ module ActiveModel
   # 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
+  # the class you're interested in observing, you can use the <tt>Observer.observe</tt>
+  # class method which takes either the concrete class (Product) or a symbol for that
   # class (:product):
   #
   #   class AuditObserver < ActiveModel::Observer
@@ -165,6 +182,7 @@ module ActiveModel
   #
   class Observer
     include Singleton
+    extend ActiveSupport::DescendantsTracker
 
     class << self
       # Attaches the observer to the supplied model classes.
@@ -208,9 +226,12 @@ module ActiveModel
       self.class.observed_classes
     end
 
-    # Send observed_method(object) if the method exists.
+    # Send observed_method(object) if the method exists and
+    # the observer is enabled for the given object's class.
     def update(observed_method, object) #:nodoc:
-      send(observed_method, object) if respond_to?(observed_method)
+      return unless respond_to?(observed_method)
+      return if disabled_for?(object)
+      send(observed_method, object)
     end
 
     # Special method sent by the observed class when it is inherited.
@@ -224,5 +245,11 @@ module ActiveModel
       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