Confirm a record has not already been destroyed before decrementing

counter cache

At present, calling destroy multiple times on the same record results
in the belongs_to counter cache being decremented multiple times. With
this change the record is checked for whether it is already destroyed
prior to decrementing the counter cache.

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Confirm a record has not already been destroyed before decrementing counter cache.
+
+    *Ben Tucker*
+
 *   Mute `psql` output when running rake db:schema:load.
 
     *Godfrey Chan*

activerecord/lib/active_record/associations/builder/belongs_to.rb

@@ -34,7 +34,9 @@ module ActiveRecord::Associations::Builder
         def belongs_to_counter_cache_before_destroy_for_#{name}
           unless destroyed_by_association && destroyed_by_association.foreign_key.to_sym == #{foreign_key.to_sym.inspect}
             record = #{name}
-            record.class.decrement_counter(:#{cache_column}, record.id) unless record.nil?
+            if record && !self.destroyed?
+              record.class.decrement_counter(:#{cache_column}, record.id)
+            end
           end
         end
 

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -414,6 +414,26 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal 15, topic.replies.size
   end
 
+  def test_counter_cache_double_destroy
+    topic = Topic.create :title => "Zoom-zoom-zoom"
+
+    5.times do
+      topic.replies.create(:title => "re: zoom", :content => "speedy quick!")
+    end
+
+    assert_equal 5, topic.reload[:replies_count]
+    assert_equal 5, topic.replies.size
+
+    reply = topic.replies.first
+
+    reply.destroy
+    assert_equal 4, topic.reload[:replies_count]
+
+    reply.destroy
+    assert_equal 4, topic.reload[:replies_count]
+    assert_equal 4, topic.replies.size
+  end
+
   def test_custom_counter_cache
     reply = Reply.create(:title => "re: zoom", :content => "speedy quick!")
     assert_equal 0, reply[:replies_count]