You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 20230621103043_replace_old_fk_ci_job_variables_to_builds_v2.rb
    path of file: ./repos/gitlabhq/db/post_migrate
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class ReplaceOldFkCiJobVariablesToBuildsV2 < Gitlab::Database::Migration[2.1]
  disable_ddl_transaction!

  def up
    return if new_foreign_key_exists?

    with_lock_retries do
      remove_foreign_key_if_exists :ci_job_variables, :ci
    
  def down
    return unless new_foreign_key_exists?

    add_concurrent_foreign_key :ci_job_variables, :ci_builds,
      name: :temp_fk_rails_fbf3b34792_p,
      column: [:partition_id, :job_id],
      target_column: [:partition_id, :id],
      on_update: :cascade,
      on_delete: :cascade,
      validate: true,
      reverse_lock_order: true

    switch_constraint_names :ci_job_variables, :fk_rails_fbf3b34792_p, :temp_fk_rails_fbf3b34792_p
  end