delete old file(Example in http://guides.rubyonrails.org/active_record_validations_callbacks.html#callbacks-overview 18 Transaction Callbacks)

deleet_file.rb

class PictureFile < ActiveRecord::Base
  attr_accessor :delete_file
 
  after_destroy do |picture_file|
    picture_file.delete_file = picture_file.filepath
  end
 
  after_commit do |picture_file|
    if picture_file.delete_file && File.exist?(picture_file.delete_file)
      File.delete(picture_file.delete_file)
      picture_file.delete_file = nil
    end
  end
end