From: Stephen Bannasch <stephen.bannasch@...>
Date: 2006-04-11T05:24:03+09:00
Subject: class variables and inheritance (ActiveRecord problem)

I'm new to Ruby and I'd like to be able to derive from a class and 
define a new class variable to replace a class variable in the parent 
class -- however I also want the original class to have access to 
it's original class variable.

Here's my simple test program:

class Klass
  cattr_accessor :prefix
   @@prefix = ''
   def Klass.show(string)
     puts @@prefix + string
   end
end

class DerivedKlass < Klass
   cattr_accessor :prefix
   @@prefix = ''
end

Klass.prefix = "123"
Klass.show("abc") # => "123abc"
DerivedKlass.prefix = "789"
DerivedKlass.show("abc")# => "789abc"
Klass.show("abc") # => "789abc"

I'd like Klass.show("abc") to instead produce "123abc".

The reason I'd think I'd like to do it this way is that I need to 
change how ActiveRecord works. Here's my problem:

I have 2 different ActiveRecord connections open and one of them is 
to a shared database so I set the following class variable:

ActiveRecord::Base.table_name_prefix = 'myapp_'

So while I refer to the table 'users' in my code in the database the 
table is actually named 'myapp_users'.

However the other connection is to a legacy database and I need to 
access the tables in this database without the table_name_prefix.

If this can't be done perhaps I could do something in DerivedKlass so 
that any accesses to it's actual or inherited object methods save 
Klass.prefix, replace it, and restore it? Of course the restoration 
would have to work for both normal program flow and for an error. 
This sounds uglier to me.

Thanks for any advice.

-- 
- Stephen Bannasch
   Concord Consortium, http://www.concord.org