gistfile1.rb

# create table users (id integer auto_increment, primary key (id));
# create table items (id integer auto_increment, user_id integer, primary key (id));
# insert into users (id) values (1);
# insert into items (user_id) values (1);

% cat a.rb
require 'rubygems'
require 'active_support/dependencies'
require 'active_record'

ActiveRecord::Base.establish_connection(
  # DB settings
)

class User < ActiveRecord::Base
  has_many :items
end

begin
  require 'item'
rescue
end

module X
end

require 'item'

u = User.first
item = u.items.first
p item
p item.class
p item.class.object_id
p Item.object_id


% cat item.rb
class Item < ActiveRecord::Base
  include X
end