Touch objects in a has_and_belongs_to_many association

On has_many relations, there is a simple way to update all associated objects - just add touch: true and the updated_at field on all associated objects will get updated. This is a major issue with Russian Doll caching, because this is was expires the cache and makes sure the page shows the most recent changes. However has_and_belongs_to_many (HABTM) does not have a :touch option. It must be done manually. So, here's a quick and easy way to do this:

  class Category
    before_save :touch_videos

    def touch_videos
      videos.touch
    end
  end

  class Video
    def self.touch
      update_all(updated_at: Time.now)
      # or, if you need validations to run for some reason
      find_each { |video| video.touch }
    end
  end