prepare_instances_to_run_callbacks_on

# File activerecord/lib/active_record/connection_adapters/abstract/transaction.rb, line 267
        def prepare_instances_to_run_callbacks_on(records)
          records.each_with_object({}) do |record, candidates|
            next unless record.trigger_transactional_callbacks?

            earlier_saved_candidate = candidates[record]

            next if earlier_saved_candidate && record.class.run_commit_callbacks_on_first_saved_instances_in_transaction

            # If the candidate instance destroyed itself in the database, then
            # instances which were added to the transaction afterwards, and which
            # think they updated themselves, are wrong. They should not replace
            # our candidate as an instance to run callbacks on
            next if earlier_saved_candidate&.destroyed? && !record.destroyed?

            # If the candidate instance was created inside of this transaction,
            # then instances which were subsequently loaded from the database
            # and updated need that state transferred to them so that
            # the after_create_commit callbacks are run
            record._new_record_before_last_commit = true if earlier_saved_candidate&._new_record_before_last_commit

            # The last instance to save itself is likeliest to have internal
            # state that matches what's committed to the database
            candidates[record] = record
          end
        end