From: Todd Benson <caduceass@...>
Date: 2008-02-08T18:44:53+09:00
Subject: Re: Multilevel class inheritance not working as expected

On Feb 8, 2008 3:10 AM, Jörg Battermann <jb@joergbattermann.com> wrote:
> Hello there,
>
> I am having a problem inheriting an already inherited class. errr..
> sounds more complicated than it is.. look:
>
> class Item < ActiveRecord::Base
> # has a name and description field
> end
>
> class Reference < Item
> # has a something field
> end
>
> class UrlReference < Reference
> #has an url field
> end
>
> ... now If I do make a u = UrlReference.new in the console for
> example, the 'u' instance does NOT have the url field.. only the ones
> from Reference and Item...
>
>
> How come? I guess that's basic ruby.. but how do I properly inherit
> from other classes which again inherit from other ones? Did I miss
> something here?
>
> Cheers & thanks,

Hmm, not sure.  I think maybe the problem lies within your database
schema or your use of "single table inheritance" with ActiveRecord.

Class inheritance in pure Ruby is easy...

class A
  def initialize; @a=nil; end
end
class B < A
  def initialize; super; @b=nil; end
end
class C < B
  def initialize; super;  @c=nil; end
end
c = C.new
puts c.inspect

=> #<C:0x2df0848 @c=nil, @a=nil, @b=nil>

Todd