* Use ActiveRecord::Result#to_ary instead of deprecated to_hash
They do the same thing, and to_hash has been removed from Rails 6.1
* Explicitly name polymorphic indexes to workaround a bug in Rails 6.1
cf. https://github.com/rails/rails/issues/41693
* Fix incorrect usage of “foreign_key” in migration script
* Use `ActiveModel::Errors#delete` instead of deprecated clear method
* Fix link headers tests on Rails 6.1
Rails 6.1 adds values to the Link header by default, thus it is not a
LinkHeader object anymore. Fix the test to parse the Link header instead
of assuming it is a LinkHeader.
Include a dummy Account class in the migration script containing only the
attributes relevant to the migration in order to not rely as much on the
codebase being in sync with the database schema.
* Wrong exception class: ActiveRecord::RecordNotUnique, not PG::UniqueViolation
It's completely not obvious but PG::UniqueViolation is just a string inside the exception message, not the actual class of the exception
* Favourite does not have target_account_id
* Improve account index migration
- Display more progress in stdout
- Catch PG::UniqueViolation when re-attributing favourites
- Skip callbacks and validations when re-attributing other relationships
* Use in_batches to reduce table lock-up during account merge
* Use #say_with_time to benchmark each deduplication
