backport of fix for issue #7630

3 files changed, 23 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 99bef61407..7666b8f11f 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Fix counter cache columns not updated when replacing `has_many :through`
+    associations.
+    Backport #8400.
+    Fix #7630.
+
+    *Matthew Robertson*
+
 *   Don't update `column_defaults` when calling destructive methods on column with default value.
     Backport c517602.
     Fix #6115.
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 53d49fef2e..2b9e7ea55d 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -139,6 +139,11 @@ module ActiveRecord
 
           delete_through_records(records)
 
+          if source_reflection.options[:counter_cache]
+            counter = source_reflection.counter_cache_column
+            klass.decrement_counter counter, records.map(&:id)
+          end
+
           if through_reflection.macro == :has_many && update_through_counter?(method)
             update_counter(-count, through_reflection)
           end
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index 40d2e9568d..277a3bddaa 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -346,6 +346,17 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
   end
 
+  def test_update_counter_caches_on_replace_association
+    post = posts(:welcome)
+    tag  = post.tags.create!(:name => 'doomed')
+    tag.tagged_posts << posts(:thinking)
+
+    tag.tagged_posts = []
+    post.reload
+
+    assert_equal(post.taggings.count, post.taggings_count)
+  end
+
   def test_replace_association
     assert_queries(4){posts(:welcome);people(:david);people(:michael); posts(:welcome).people(true)}