Merge pull request #21092 from vngrs/use_memoization_for_ids_reader

Use memoization for collection associations ids reader

activerecord/lib/active_record/associations/collection_association.rb

@@ -62,8 +62,10 @@ def ids_reader
             record.send(reflection.association_primary_key)
           end
         else
-          column  = "#{reflection.quoted_table_name}.#{reflection.association_primary_key}"
-          scope.pluck(column)
+          @association_ids ||= (
+            column = "#{reflection.quoted_table_name}.#{reflection.association_primary_key}"
+            scope.pluck(column)
+          )
         end
       end
 

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -2308,4 +2308,12 @@ def test_destroy_with_bang_bubbles_errors_from_associations
 
     assert_instance_of PostWithErrorDestroying, error.record
   end
+
+  def test_ids_reader_memoization
+    car = Car.create!(name: 'Tofaş')
+    bulb = Bulb.create!(car: car)
+
+    assert_equal [bulb.id], car.bulb_ids
+    assert_no_queries { car.bulb_ids }
+  end
 end