Merge pull request rails#12748 from dm1try/fix_counter_cache_for_through_association

Fixes rails#11079, prevent the counter cache from being decremented twice when destroying a record on a has_many :through association

Author: senny

activerecord/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Prevent the counter cache from being decremented twice when destroying
+    a record on a has_many :through association.
+
+    Fixes #11079.
+
+    *Dmitry Dedov*
+
 *   Unify boolean type casting for `MysqlAdapter` and `Mysql2Adapter`.
     `type_cast` will return `1` for `true` and `0` for `false`.
 

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -163,7 +163,7 @@ def delete_records(records, method)
 
           delete_through_records(records)
 
-          if source_reflection.options[:counter_cache]
+          if source_reflection.options[:counter_cache] && method != :destroy
             counter = source_reflection.counter_cache_column
             klass.decrement_counter counter, records.map(&:id)
           end

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -514,6 +514,15 @@ def test_update_counter_caches_on_replace_association
     assert_equal(post.taggings.count, post.taggings_count)
   end
 
+  def test_update_counter_caches_on_destroy
+    post = posts(:welcome)
+    tag  = post.tags.create!(name: 'doomed')
+
+    assert_difference 'post.reload.taggings_count', -1 do
+      tag.tagged_posts.destroy(post)
+    end
+  end
+
   def test_replace_association
     assert_queries(4){posts(:welcome);people(:david);people(:michael); posts(:welcome).people(true)}