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: 20231028225001_add_position_to_hold.rb
    path of file: ./repos/circulate/db/migrate
    
    the code of the file until where you have to start completion: class AddPositionToHold < ActiveRecord::Migration[6.
    
  def up
    add_column :holds, :position, :integer

    MigrationItem.find_each do |item|
      item.holds.order(:created_at).each.with_index(1) do |hold, index|
        hold.update_column :position, index
      end
    end

    change_column_null :holds, :position, false

    add_index :holds, [:item_id, :position], unique: true
  end