has_one children being updated with parent record

[georgedrummond]

There is currently an issue on rails 4.2 and mysql where children of a has_one relationship are having their UUID updated at the same time as the parent. The strange thing is that a mysql UPDATE query is run overwriting the exact same data.

To replicate the issue I have created a dummy app with a failing test suite. In the example we have Owner has_one Dog which does not use activeuuid and displays the rails default behaviour. We also have User has_one Car which does use uuid.

If we first take Owner has_one Dog we can confirm that the Dog record is never touched when updating the Owner.

o = Owner.create
   (0.1ms)  BEGIN
  SQL (0.2ms)  INSERT INTO `owners` (`created_at`, `updated_at`) VALUES ('2015-06-03 21:05:23', '2015-06-03 21:05:23')
   (0.2ms)  COMMIT
=> #<Owner id: 1, name: nil, created_at: "2015-06-03 21:05:23", updated_at: "2015-06-03 21:05:23">
irb(main):005:0> o.create_dog
   (0.1ms)  BEGIN
  SQL (0.2ms)  INSERT INTO `dogs` (`owner_id`, `created_at`, `updated_at`) VALUES (1, '2015-06-03 21:05:27', '2015-06-03 21:05:27')
   (0.3ms)  COMMIT
  Dog Load (0.2ms)  SELECT  `dogs`.* FROM `dogs` WHERE `dogs`.`owner_id` = 1 LIMIT 1
=> #<Dog id: 1, owner_id: 1, created_at: "2015-06-03 21:05:27", updated_at: "2015-06-03 21:05:27">
irb(main):006:0> o.update name: 'George'
   (0.2ms)  BEGIN
  SQL (0.5ms)  UPDATE `owners` SET `name` = 'George', `updated_at` = '2015-06-03 21:05:34' WHERE `owners`.`id` = 1
   (6.4ms)  COMMIT
=> true

Next lets try again with User has_one Car which does use activeuuid. Our Car record should not be touched when updating the Owner.

u = User.create
   (0.1ms)  BEGIN
  SQL (0.2ms)  INSERT INTO `users` (`id`, `created_at`, `updated_at`) VALUES (x'69704d2f29cd4bc484fa9545b8c54a55', '2015-06-03 21:04:54', '2015-06-03 21:04:54')
   (0.2ms)  COMMIT
=> #<User id: #<UUID:0x3ff7ae5768f0 UUID:69704d2f-29cd-4bc4-84fa-9545b8c54a55>, name: nil, created_at: "2015-06-03 21:04:54", updated_at: "2015-06-03 21:04:54">
irb(main):002:0> c = u.create_car
   (0.1ms)  BEGIN
  SQL (0.2ms)  INSERT INTO `cars` (`id`, `user_id`, `created_at`, `updated_at`) VALUES (x'f92659de32814c7f8e05d95bc13fab72', x'69704d2f29cd4bc484fa9545b8c54a55', '2015-06-03 21:05:03', '2015-06-03 21:05:03')
   (0.3ms)  COMMIT
  Car Load (0.2ms)  SELECT  `cars`.* FROM `cars` WHERE `cars`.`user_id` = x'69704d2f29cd4bc484fa9545b8c54a55' LIMIT 1
=> #<Car id: #<UUID:0x3ff7adb9276c UUID:f92659de-3281-4c7f-8e05-d95bc13fab72>, user_id: #<UUID:0x3ff7ae5768f0 UUID:69704d2f-29cd-4bc4-84fa-9545b8c54a55>, make: nil, created_at: "2015-06-03 21:05:03", updated_at: "2015-06-03 21:05:03">
irb(main):003:0> u.update name: 'George'
   (0.2ms)  BEGIN
  SQL (0.4ms)  UPDATE `users` SET `id` = x'69704d2f29cd4bc484fa9545b8c54a55', `name` = 'George', `updated_at` = '2015-06-03 21:05:15' WHERE `users`.`id` = x'69704d2f29cd4bc484fa9545b8c54a55'

  ######################################

  SQL (0.2ms)  UPDATE `cars` SET `id` = x'f92659de32814c7f8e05d95bc13fab72', `user_id` = x'69704d2f29cd4bc484fa9545b8c54a55', `updated_at` = '2015-06-03 21:05:15' WHERE `cars`.`id` = x'f92659de32814c7f8e05d95bc13fab72'

  ######################################

   (6.2ms)  COMMIT
=> true

From the logs we can see that the Car had its id and user_id updated along with the timestamps.

Has anyone else experienced this problem or come up with a fix?

[georgedrummond]

I think this issue is related to the UUID being a serialized object