1 files changed, 15 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/observer.rb b/activerecord/lib/active_record/observer.rb
index a34ff4a47a..4e05b819b5 100644
--- a/activerecord/lib/active_record/observer.rb
+++ b/activerecord/lib/active_record/observer.rb
@@ -1,6 +1,3 @@
-require 'singleton'
-require 'set'
-
 module ActiveRecord
   # Observer classes respond to lifecycle callbacks to implement trigger-like
   # behavior outside the original class. This is a great way to reduce the
@@ -88,11 +85,17 @@ module ActiveRecord
   # singletons and that call instantiates and registers them.
   #
   class Observer < ActiveModel::Observer
+    extlib_inheritable_accessor(:observed_methods){ [] }
+
     def initialize
       super
       observed_subclasses.each { |klass| add_observer!(klass) }
     end
 
+    def self.method_added(method)
+      observed_methods << method if ActiveRecord::Callbacks::CALLBACKS.include?(method.to_sym)
+    end
+
     protected
       def observed_subclasses
         observed_classes.sum([]) { |klass| klass.send(:subclasses) }
@@ -100,8 +103,15 @@ module ActiveRecord
 
       def add_observer!(klass)
         super
-        if respond_to?(:after_find) && !klass.method_defined?(:after_find)
-          klass.class_eval 'def after_find() end'
+
+        # Check if a notifier callback was already added to the given class. If
+        # it was not, add it.
+        self.observed_methods.each do |method|
+          callback = :"_notify_observers_for_#{method}"
+          if (klass.instance_methods & [callback, callback.to_s]).empty?
+            klass.class_eval "def #{callback}; notify_observers(:#{method}); end"
+            klass.send(method, callback)
+          end
         end
       end
   end