From: Brian Candler <b.candler@...>
Date: 2010-06-08T23:22:57+09:00
Subject: Re: Looking for ORM for 'legacy' database.

Brian Candler wrote:
> class Playlist < ActiveRecord::Base
>   self.table_name = 'venue_playlist'
>   self.primary_key = 'plt_id'
> 
>   # Similarly for foreign key relations
>   has_many :playlist_items, :foreign_key => 'pli_playlist_id',
>         :order => 'pli_order', :dependent => :delete_all
> end

And for reference, here's the relation from the other side:

class PlaylistItem < ActiveRecord::Base
  self.table_name = 'playlist_item'
  self.primary_key = 'nonexistent'
  belongs_to :playlist, :foreign_key=>'pli_playlist_id'
end

Notice that this particular table didn't really have a primary key as 
such; each row was a unique tuple. Setting the primary_key to 
'nonexistent' just proves that AR never attempted to use it.

At the controller side, all I needed to do was to set the attributes I 
was interested in when creating the object.

  def add_item
    ...
    PlaylistItem.create!(
        :pli_playlist_id => @playlist.plt_id,
        :pli_track_id => ...
        :pli_order => ...
    )
    ...
  end
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