From: Kirk Haines <khaines@...>
Date: 2004-06-05T01:25:14+09:00
Subject: Re: [ANN] Active Record 0.8.2: Inheritable callback ques

On Sat, 5 Jun 2004 00:41:55 +0900, Carl Youngblood wrote

> I usually prefer to name my primary ID columns <tablename>id just to 
> avoid confusion.  For example, the primary key of the user table is 
> called userid.  On many-table JOINS it gets confusing to have a lot 
> of IDs floating around.  So I agree that being able to change the id 
> column to something else would be handy.  Another thing that some 
> people might be confused about is when you have a table whose 
> primary key consists of multiple columns that are combinatorially 
> unique.  In these cases I think the solution is to add an integer 
> primary key and use it for the ID column, and then make a unique 
> index across the fields that you wish to be combinatorially unique.

I still haven't delved into ActiveRecord's code as much as I want to, but in 
theory these things should be supportable.

Kansas, which is similar to ActiveRecord but takes a few different 
approaches, allows things like this:

create table jukebox (
  id int unsigned primary key,
  serial_number int unsigned unique,
  blah blah blah)

create table albums (
  id int unsigned primary key,
  jukebox_serial int,
  blah blah blah)

create table tracks (
  id int unsigned primary key,
  album_id int,
  blah blah blah)

class Jukebox
  to_many(:albums, :Albums, :jukebox_serial, :serial_number)
end

class Albums
  to_many(:tracks, :Tracks, :album_id)
  belongs_to(:jukebox, :Jukebox, :serial_number, :jukebox_serial)
end

class Tracks
  belongs_to(:album, :Albums, :album_id)
end


So, a Jukebox has many Albums.  However, instead of using Jukebox's primary 
key, serial_number on the Jukebox maps to jukebox_serial, which is simply a 
unique key, on the Album.

Albums have many tracks, and are correlated through the primary key on Album 
and the album_id field on Track.  An Album also belongs to a Jukebox, and is 
correlated via the jukebox_serial field on the Album and the serial_number 
field on the Jukebox.

Tracks belong to an Album, and are correlated via the album_id field of the 
Track to the primary key of the Album.

I don't yet have complete support for multiple field primary keys, but 
that's not far off.  There is a release with some added documentation 
explaining the stuff above, among other things, coming hopefully by the end 
of the day.


Kirk Haines