Rails - Aug 2006 - insert into database failing

hi all,

i am trying a little project based on the agile book''s shopping cart
example and have hit a problem. the inserts are failing when saving a
quote which contains line_items. the models are as follows
(quote_line_item is using single table inheritance):

class Quote < ActiveRecord::Base
	has_many :quote_line_items
end

class LineItem < ActiveRecord::Base
end

class QuoteLineItem < LineItem
	belongs_to :quote
	belongs_to :product
end

the section of code that actually fails is here (labelled)

def send_quote
	@quote = Quote.new(params[:quote])
	@quote.quote_line_items << @cart.items
	if @quote.save  # <---- error occurs here
		@cart.empty!
		redirect_to_index(''Thanks for requesting a quote. We will be in
contact with you shortly'')
	else
		redirect_to :action => ''details''
	end
end

it fails with the following (note the values to be inserted are actually
objects that have not been dereferenced:

INSERT INTO line_items (`order_id`, `quote_id`, `updated_at`,
`created_by`, `product_id`, `quantity`, `type`, `updated_by`,
`unit_price`, `created_at`) VALUES(#<Quote:0xa75703d0>,
#<Quote:0xa75738a0>, #<Quote:0xa75749a8>, #<Quote:0xa756b268>,
#<Quote:0xa7561218>, #<Quote:0xa75632fc>, #<Quote:0xa7567b18>,
#<Quote:0xa755ef40>, #<Quote:0xa7559fcc>, #<Quote:0xa7553654>)

i have debugged the code and immediately before the save the objects
@quote and @cart are correct and without errors. it is a little
confusing. without STI it seems to work fine. i have never received
errors like this before although i have not used STI before.

any suggestions would be greatly appreciated.

-felix