gistfile1.txt

create_table "parents", :force => true do |t|
  t.column "name", :string
  t.column "type", :string
end

###



class Parent < ActiveRecord::Base
end

class Child < Parent
end

class SubChild < Child
end

####

ruby-1.8.7-p302 > Child.all.size
 => 16 
DEBUG      Child Load (0.6ms)   SELECT * FROM `parents` WHERE ( (`parents`.`type` = 'Child' ) ) 

ruby-1.8.7-p302 > SubChild.all
 => [#<SubChild>] 

DEBUG      SubChild Columns (72.4ms)   SHOW FIELDS FROM `parents`
DEBUG      SubChild Load (3.9ms)   SELECT * FROM `parents` WHERE ( (`parents`.`type` = 'SubChild' ) ) 

ruby-1.8.7-p302 > Child.all.size
 => 17 

^[4DEBUG      Child Load (0.9ms)   SELECT * FROM `parents` WHERE ( (`parents`.`type` = 'Child' OR `parents`.`type` = 'SubChild' ) )