Advice for superset/subset data model

Rails
1

Hi,

I’m interested to know if anyone has any clever suggestions about how
to model the following scenario with ActiveRecord:

  • I’d like a collection of media, including photos, videos, and songs,
    all of which have some common and unique properties
  • I start with a “media” table, that includes things like id, creation
    date, name, description, and filename
  • the media table also has a media_type_id that maps to another table,
    media_types, that has IDs for each of the three types of media
  • then there are tables for each specific media type, so the photos
    table has photographer_name, subject_name, etc; the videos table has
    duration, format, etc; and the songs table has artist, duration, etc
  • each of the specific tables also has an ID column; a media_detail_id
    column in the media table maps to this ID

My ultimate goal is for a URL like /media/index to display all the
media names, and clicking on one gives the detail depending on what
kind it is. Another goal is to be able to enter all the data for,
say, a photo on one page – both the attributes for the media table
(name, description) and for the photos table (photographer name,
subject name).

I’ve been trying to work with Rails to do this simply, and it’s clear
I’m fighting against the grain of how it likes to do things. If
anyone has any suggestions, they’d be much appreciated.

Thanks,
Dan

2

This is a fairly typical polymorphic association. No need for the
‘media_types’ table at all. Each media table has a link to one photo,
or one video, or one song. Call it ‘media_detail’ for lack of a better
term.

class Media < ActiveRecord::Base
belongs_to :media_detail, :polymorphic => true
end
class Photo < ActiveRecord::Base # and same for Song and Video
has_one :media, :as => :media_detail
end

In your media table you have two columns: media_detail_type (string)
and media_detail_id (integer).

As for views, I would suggest a separate controller for each type, and
a shared partial view for the common fields.

It might be beneficial to use accepts_nested_attributes_for :media
inside each of Photo, Song, Video.