## Rails ActiveRecord

class Playlist
  serialize :items_ids
  def videos(offset = nil, limit = nil)
   ids = item_ids || []
   vs = Video.find(:all, :conditions => ["id in (?)", ids],
                         :limit => limit, :offset => offset)
   hvs = Hash[*(vs.map{|v| [v.id.to_i, v] }.flatten)]
   ids.map{|i| hvs[i.to_i] }
  end
  def add_item(v)
    self.items_id ||= []
    items_id.unshift(v.id)
    v.playlist_id = self.id
    v.save!
  end
end

list = Playlist.new
list.add_item(some_video)
list.videos(0, 2) #=> [ #<Video ...> ]

## StrokeDB

Playlist = Meta.new do
  on_initialize do |doc|
    doc["videos"] ||= []
  end
end

list = Playlist.new
list.videos << some_video  # store reference
list.videos[0, 2] #=> [ #<Video ...> ] (auto dereferencing)