Support for :counter_cache on polymorphic belongs_to

activerecord/lib/active_record/associations/belongs_to_association.rb

@@ -46,7 +46,7 @@ def update_counters(record)
 
           if counter_cache_name && @owner.persisted? && different_target?(record)
             if record
-              target_klass.increment_counter(counter_cache_name, record.id)
+              record.class.increment_counter(counter_cache_name, record.id)
             end
 
             if foreign_key_present

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -567,4 +567,16 @@ def test_reloading_association_with_key_change
     client.client_of = companies(:first_firm).id
     assert_equal companies(:first_firm), firm.reload
   end
+
+  def test_polymorphic_counter_cache
+    tagging = taggings(:welcome_general)
+    post    = posts(:welcome)
+    comment = comments(:greetings)
+
+    assert_difference 'post.reload.taggings_count', -1 do
+      assert_difference 'comment.reload.taggings_count', +1 do
+        tagging.taggable = comment
+      end
+    end
+  end
 end

activerecord/test/schema/schema.rb

@@ -143,6 +143,7 @@ def create_table(*args, &block)
       t.text    :body, :null => false
     end
     t.string  :type
+    t.integer :taggings_count, :default => 0
   end
 
   create_table :companies, :force => true do |t|