Revert "Revert "belongs_to :touch behavior now touches old associat…

…ion when transitioning to new association" until a proper fix is found for #10197"

This reverts commit 7389df1.

Conflicts:
	activerecord/test/cases/timestamp_test.rb

activerecord/CHANGELOG.md

@@ -110,6 +110,26 @@
 
     *Neeraj Singh*
 
+*   `belongs_to :touch` behavior now touches old association when
+    transitioning to new association.
+
+        class Passenger < ActiveRecord::Base
+          belongs_to :car, touch: true
+        end
+
+        car_1 = Car.create
+        car_2 = Car.create
+
+        passenger = Passenger.create car: car_1
+
+        passenger.car = car_2
+        passenger.save
+
+    Previously only car_2 would be touched. Now both car_1 and car_2
+    will be touched.
+
+    *Adam Gamble*
+
 *   Extract and deprecate Firebird / Sqlserver / Oracle database tasks, because
     These tasks should be supported by 3rd-party adapter.
 

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

@@ -67,8 +67,19 @@ def belongs_to_counter_cache_after_update_for_#{name}
     def add_touch_callbacks(reflection)
       mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
         def belongs_to_touch_after_save_or_destroy_for_#{name}
-          record = #{name}
+          foreign_key_field = #{reflection.foreign_key.inspect}
+          old_foreign_id    = attribute_was(foreign_key_field)
+
+          if old_foreign_id
+            reflection_klass = #{reflection.klass}
+            old_record       = reflection_klass.find_by(reflection_klass.primary_key => old_foreign_id)
+
+            if old_record
+              old_record.touch #{options[:touch].inspect if options[:touch] != true}
+            end
+          end
 
+          record = #{name}
           unless record.nil? || record.new_record?
             record.touch #{options[:touch].inspect if options[:touch] != true}
           end

activerecord/test/cases/timestamp_test.rb

@@ -176,6 +176,52 @@ def self.name; 'Toy'; end
     assert_not_equal time, owner.updated_at
   end
 
+  def test_changing_parent_of_a_record_touches_both_new_and_old_parent_record
+    klass = Class.new(ActiveRecord::Base) do
+      def self.name; 'Toy'; end
+      belongs_to :pet, touch: true
+    end
+
+    toy1 = klass.find(1)
+    old_pet = toy1.pet
+
+    toy2 = klass.find(2)
+    new_pet = toy2.pet
+    time = 3.days.ago.at_beginning_of_hour
+
+    old_pet.update_columns(updated_at: time)
+    new_pet.update_columns(updated_at: time)
+
+    toy1.pet = new_pet
+    toy1.save!
+
+    old_pet.reload
+    new_pet.reload
+
+    assert_not_equal time, new_pet.updated_at
+    assert_not_equal time, old_pet.updated_at
+  end
+
+  def test_clearing_association_touches_the_old_record
+    klass = Class.new(ActiveRecord::Base) do
+      def self.name; 'Toy'; end
+      belongs_to :pet, touch: true
+    end
+
+    toy = klass.find(1)
+    pet = toy.pet
+    time = 3.days.ago.at_beginning_of_hour
+
+    pet.update_columns(updated_at: time)
+
+    toy.pet = nil
+    toy.save!
+
+    pet.reload
+
+    assert_not_equal time, pet.updated_at
+  end
+
   def test_timestamp_attributes_for_create
     toy = Toy.first
     assert_equal toy.send(:timestamp_attributes_for_create), [:created_at, :created_on]