From ee5fdbf21a4a837f59b8726c10726ddd020181f9 Mon Sep 17 00:00:00 2001
From: Kamal Fariz Mahyuddin <kamal.fariz@gmail.com>
Date: Wed, 9 Feb 2011 23:37:30 +0800
Subject: [PATCH] Fix observer callbacks firing multiple times on descendant instances

---
 activerecord/lib/active_record/observer.rb |    9 ++++++++-
 activerecord/test/cases/lifecycle_test.rb  |   14 ++++++++++++++
 2 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/activerecord/lib/active_record/observer.rb b/activerecord/lib/active_record/observer.rb
index 8b011ad..0893d7e 100644
--- a/activerecord/lib/active_record/observer.rb
+++ b/activerecord/lib/active_record/observer.rb
@@ -104,10 +104,17 @@ module ActiveRecord
 
       def define_callbacks(klass)
         observer = self
+        observer_name = observer.class.name.underscore.gsub('/', '__')
 
         ActiveRecord::Callbacks::CALLBACKS.each do |callback|
           next unless respond_to?(callback)
-          klass.send(callback){|record| observer.send(callback, record)}
+          callback_meth = :"_notify_#{observer_name}_for_#{callback}"
+          unless klass.respond_to?(callback_meth)
+            klass.send(:define_method, callback_meth) do
+              observer.send(callback, self)
+            end
+            klass.send(callback, callback_meth)
+          end
         end
       end
   end
diff --git a/activerecord/test/cases/lifecycle_test.rb b/activerecord/test/cases/lifecycle_test.rb
index 0558deb..a42f5d9 100644
--- a/activerecord/test/cases/lifecycle_test.rb
+++ b/activerecord/test/cases/lifecycle_test.rb
@@ -7,6 +7,12 @@ require 'models/comment'
 
 class SpecialDeveloper < Developer; end
 
+class DeveloperObserver < ActiveRecord::Observer
+  def before_save(developer)
+    developer.salary += 1
+  end
+end
+
 class SalaryChecker < ActiveRecord::Observer
   observe :special_developer
   attr_accessor :last_saved
@@ -196,4 +202,12 @@ class LifecycleTest < ActiveRecord::TestCase
     assert_equal developer, SalaryChecker.instance.last_saved
   end
 
+  test "callback observing the ancestor does not fire multiple times on descendent" do
+    DeveloperObserver.instance # activate
+    developer = Developer.create! :name => 'Ancestor', :salary => 100000
+    assert_equal 100001, developer.salary, 'ancestor callback fired multiple times'
+    developer = SpecialDeveloper.create! :name => 'Descendent', :salary => 100000
+    assert_equal 100001, developer.salary, 'descendent callback fired multiple times'
+  end
+
 end
-- 
1.7.3.3