id_partition doesn't work with mongodb

[ikonyshev]

according to code below (it's from interpolations.rb) id_partition function return nil for mongo ids because mongo use own id class. I think it would be great to convert id to string using .to_s to avoid such problems.
Also it seems that taking only first 3 matches for string ids can cause problems (for example my project is going to have 200-300k items with up to 30 images per item, and these 3 matches wouldn't help at all)

    def id_partition attachment, style_name
      case id = attachment.instance.id
      when Integer
        ("%09d" % id).scan(/\d{3}/).join("/")
      when String
        id.scan(/.{3}/).first(3).join("/")
      else
        nil
      end
    end

[sikachu]

Yeah, I think for mongo you'll have to write the id_partition interpolation yourself, and override the one given by paperclip.