[Bug fix] Clear changes after update

[freddiescadding-pennylane]

Current behaviour

When a record is updated using batch_update, the dirty changes are not cleared. When processing further update statements, ActiveRecord is not aware that the database has been successfully updated, and so it may not include changes that it believes to be identical to the current state of the record in the database.

Reproduction steps

A cat is making some changes:

original_name = 'Felix'
new_name = 'Felicia'

cat = Cat.create!(name: original_name)
cat.name = new_name

Cat.batch_update(
  [cat],
  validate: false,
  columns: [:name],
)
# cat.changes_to_save => { "name" => [original_name, new_name], "updated_at" => [x, y] }

# we would expect:
# cat.changes_to_save => {}

cat.name
# => new_name

cat.update!(name: original_name)
# because `name` is still in the `changes_to_save`, active record thinks its value is actually still `original_name`
# so it doesn't include it in the update statement:

# ```
# TRANSACTION (3.9ms)
# /*line:(jeancat):11:in '<main>'*/ BEGIN
#   Cat Update (10.5ms)
# /*line:(jeancat):11:in '<main>'*/
# UPDATE "cats" SET "updated_at" = '2025-06-03 15:21:33.316008'
# WHERE "cats"."id" = 8664364538
#   TRANSACTION (1.9ms)
# /*line:(jeancat):11:in '<main>'*/ COMMIT
# ```

#  => true

cat.name
# => original_name

cat.reload.name
# => new_name

cat.update!(name: new_name)
# => true

cat.name
# => new_name

cat.reload.name
# => new_name

Potential impact

In a real world application, following a batch_update further changes to the records may not be applied, even when they appear to have been successful. This could result in some highly unexpected and confusing behaviour.

Changes made

Called clear_attribute_changes on each updated entry to remove dirty changes on the updated attributes

This clears the dirty changes, and restores expected behaviour.

[jfpimentel]

Thanks Freddie 😉

[quentindemetz]

Good find 👌🏻