mongomapper_polymorphic.rb

require 'mongomapper'

class Media
  include MongoMapper::EmbeddedDocument
  key :file, String
end

class Video < Media
  key :length, Integer
end

class Image < Media
  key :width, Integer
  key :height, Integer
end

class Music < Media
  key :bitrate, String
end

class Catalog
  include MongoMapper::Document
  
  many :medias, :polymorphic => true
end

catalog = Catalog.new
catalog.medias = [
  Video.new("file" => "video.mpg", "length" => 3600),
  Music.new("file" => "music.mp3", "bitrate" => "128kbps"),
  Image.new("file" => "image.png", "width" => 800, "height" => 600)
]
catalog.save #=> true

from_db = Catalog.find(catalog.id)
from_db.medias.size #=> 3
from_db.medias[0].file #=> "video.mpg"
from_db.medias[0].length #=> 3600
from_db.medias[1].file #=> "music.mp3"
from_db.medias[1].bitrate #=> "128kbps"
from_db.medias[2].file #=> "image.png"
from_db.medias[2].width #=> 800
from_db.medias[2].height #=> 600