Merge PR #19759

Fix for has_and_belongs_to_many & has_many_through associations

activerecord/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Improved partial writes with HABTM and has many through associations
+    to fire database query only if relation has been changed.
+
+    Fixes #19663.
+
+    *Mehmet Emin İNAÇ*
+
 *   Deprecate passing arguments and block at the same time to
     `ActiveRecord::QueryMethods#select`.
 

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -86,7 +86,10 @@ module ActiveRecord
         end
 
         def save_through_record(record)
-          build_through_record(record).save!
+          association = build_through_record(record)
+          if association.changed?
+            association.save!
+          end
         ensure
           @through_records.delete(record.object_id)
         end

activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb

@@ -1012,4 +1012,17 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     user = User.create!
     assert_nothing_raised { user.jobs_pool.clear }
   end
+
+  def test_has_and_belongs_to_many_while_partial_writes_false
+    begin
+      original_partial_writes = ActiveRecord::Base.partial_writes
+      ActiveRecord::Base.partial_writes = false
+      developer = Developer.new(name: "Mehmet Emin İNAÇ")
+      developer.projects << Project.new(name: "Bounty")
+
+      assert developer.save
+    ensure
+      ActiveRecord::Base.partial_writes = original_partial_writes
+    end
+  end
 end