Sort photos in Rails using FIND_IN_SET MySQL function

sort_photos.rb

# TODO can be optimized to use custom class and `model_ids` method

module SortPhotos
  def sort_photos!(ids)
    raise ArgumentError, "ids isn't an array" if !ids.is_a?(Array)
    ids.map!(&:to_i)
    old_ids = self.photo_ids
    ids = ids - (ids - old_ids)
    raise ArgumentError, "Not all the ids were passed to sort! method" if old_ids.size != ids.size
    reflections[:photos].klass.update_all(['position = FIND_IN_SET(id, ?)', ids.join(',')], {:id => ids})
  end
end