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: convert_credit_card_validation_data_to_hashes.rb
    path of file: ./repos/gitlabhq/lib/gitlab/background_migration
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module Gitlab
  module BackgroundMigration
    # Converts a credit card's expiration_date, last_digits, network & holder_name
    # to hash and store values in new columns
    class ConvertCreditCardValidationDataToHashes < BatchedMigrationJob
      operation_name :convert_credit_card_data
      feature_category :user_profile

      class CreditCardValidation < ApplicationRecord # rubocop:disable Style/Documentation
        self.table_name = 'user_credit_card_validations'
      end

      def perform
        each_sub_batch do |sub_batch|
        
    
      def perform
        each_sub_batch do |sub_batch|
          credit_cards = CreditCardValidation.where(user_id: sub_batch)

          credit_card_hashes = credit_cards.map do |c|
            {
              user_id: c.user_id,
              credit_card_validated_at: c.credit_card_validated_at,
              last_digits_hash: hashed_value(c.last_digits),
              holder_name_hash: hashed_value(c.holder_name&.downcase),
              network_hash: hashed_value(c.network&.downcase),
              expiration_date_hash: hashed_value(c.expiration_date&.to_s)
            }
          end

          CreditCardValidation.upsert_all(credit_card_hashes)
        end
      end