gistfile1.rb

# replace file basename with a UUID when uploaded
# e.g.: avatar.jpg becomes 41bf830f-80cf-4efe-ad90-3b29bc6708b5.jpg
# but don't regenerate a UUID each time file url is accessed
class User < ActiveRecord::Base
  has_attached_file :avatar, path: ":basename.:extension"

  before_validation { set_avatar_file_name }

  def set_avatar_file_name
    # replace any NEW filename with a UUID
    # NOTE: if user uploads a new image with the exact filename as the most recently assigned UUID, this will break!
    if avatar_file_name_changed?
      set_avatar_file_name_to_uuid
    end
  end

  def set_avatar_file_name_to_uuid
    self.avatar_file_name = SecureRandom.uuid + File.extname(avatar_file_name)
  end
end