cakephp one to many custom relation joins

Submitted by Derick Ng on 6 October 2009 - 1:46pm

I have an Order table which has many IPN. However, I am not using cakephp conventions because the IPN table is from Paypal. I want to join the order table's order_num field to the IPN table's custom field. So it would be like:
select * from orders left join ipn on orders.order_num = ipn.custom

How do I set up the model relation correctly in models/order.php.