gistfile1.rb

class PurchaseOrder < ActiveRecord::Base
  has_one :address_linking, :as => :address_linkable, :dependent => :destroy
  has_one :address, :through => :address_linking
end

class AddressLinking < ActiveRecord::Base
  belongs_to :address
  belongs_to :address_linkable, :polymorphic => true
end

class Address < ActiveRecord::Base
  has_many :address_linkings
end

gistfile2.rb

  def update
    @purchase_order = PurchaseOrder.find(params[:id])

    if @purchase_order.update_attributes(params[:purchase_order])
      redirect_to_index("Purchase Order was successfully updated")
    else
      render :action => "edit"
    end
  end

gistfile3.txt

Processing Admin::PurchaseOrderController#update (for 127.0.0.1 at 2008-12-08 20:14:35) [PUT]
  Session ID: 3bf4103250cf261cdbc4356c77c2b62a
  Parameters: {"commit"=>"Update Purchase Order", "action"=>"update", "_method"=>"put", "id"=>"1", "purchase_order"=>{"supplier_id"=>"1", "user_id"=>"1", "address"=>{"address1"=>"NEW PURCHASE ORDER ADDRESS", "address2"=>"", "postcode"=>"", "county"=>"", "id"=>"1", "town"=>""}}, "controller"=>"admin/purchase_order"}
  User Columns (1.7ms)   SHOW FIELDS FROM `users`
  User Load (0.3ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) LIMIT 1
  PurchaseOrder Columns (1.3ms)   SHOW FIELDS FROM `purchase_orders`
  PurchaseOrder Load (0.5ms)   SELECT * FROM `purchase_orders` WHERE (`purchase_orders`.`id` = 1) 
  AddressLinking Columns (2.3ms)   SHOW FIELDS FROM `address_linkings`
  AddressLinking Load (0.5ms)   SELECT * FROM `address_linkings` WHERE (`address_linkings`.address_linkable_id = 1 AND `address_linkings`.address_linkable_type = 'PurchaseOrder') LIMIT 1
  SQL (0.1ms)   BEGIN
##########
##### WHY IS THIS USING THE Address.id (the class' id)??
##########
>>>>>  AddressLinking Update (0.2ms)   UPDATE `address_linkings` SET `address_id` = 32574510 WHERE `id` = 456
  SQL (0.5ms)   COMMIT