Modifies belong_to touch callback to touch old associations also #9091

3 files changed, 34 insertions, 10 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f73fc9d9a3..7dbfad4473 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -447,6 +447,28 @@
     *Aaron Stone + Rafael Mendonça França*
 
 *   `Relation#merge` now only overwrites where values on the LHS of the
+=======
+*   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*
+
+*   Relation#merge now only overwrites where values on the LHS of the
     merge. Consider:
 
         left  = Person.where(age: [13, 14, 15])
diff --git a/activerecord/lib/active_record/associations/builder/belongs_to.rb b/activerecord/lib/active_record/associations/builder/belongs_to.rb
index 97b1ff18e2..6b479968c8 100644
--- a/activerecord/lib/active_record/associations/builder/belongs_to.rb
+++ b/activerecord/lib/active_record/associations/builder/belongs_to.rb
@@ -48,6 +48,16 @@ module ActiveRecord::Associations::Builder
         def belongs_to_touch_after_save_or_destroy_for_#{name}
           record = #{name}
 
+          foreign_key_field   = #{reflection.foreign_key}
+          if changed_attributes.key?(foreign_key_field)
+            reflection_klass  = #{reflection.klass}
+            old_foreign_id    = changed_attributes[foreign_key_field]
+            old_record        = reflection_klass.where(foreign_key_field.to_sym => old_foreign_id).first
+            if old_record
+              old_record.touch #{options[:touch].inspect if options[:touch] != true}
+            end
+          end
+
           unless record.nil? || record.new_record?
             record.touch #{options[:touch].inspect if options[:touch] != true}
           end
diff --git a/activerecord/test/cases/timestamp_test.rb b/activerecord/test/cases/timestamp_test.rb
index 6f983bce75..0c13bb946a 100644
--- a/activerecord/test/cases/timestamp_test.rb
+++ b/activerecord/test/cases/timestamp_test.rb
@@ -176,7 +176,7 @@ class TimestampTest < ActiveRecord::TestCase
     assert_not_equal time, owner.updated_at
   end
 
-  def test_changing_parent_of_a_record_touches_both_new_and_old_parent_record_and_grandparent_record
+  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
@@ -184,30 +184,22 @@ class TimestampTest < ActiveRecord::TestCase
 
     toy1 = klass.find(1)
     old_pet = toy1.pet
-    old_owner = old_pet.owner
 
     toy2 = klass.find(2)
     new_pet = toy2.pet
-    new_owner = new_pet.owner
     time = 3.days.ago
 
     old_pet.update_columns(updated_at: time)
-    old_owner.update_columns(updated_at: time)
     new_pet.update_columns(updated_at: time)
-    new_owner.update_columns(updated_at: time)
 
     toy1.pet = new_pet
     toy1.save!
 
     old_pet.reload
-    old_owner.reload
     new_pet.reload
-    new_owner.reload
 
-    assert_not_equal time, old_pet.updated_at
-    assert_not_equal time, old_owner.updated_at
     assert_not_equal time, new_pet.updated_at
-    assert_not_equal time, new_owner.updated_at
+    assert_not_equal time, old_pet.updated_at
   end
 
   def test_timestamp_attributes_for_create