What is the best way to get the running total of a number field in child records. Let say I have an Order model, which has_many :line_items, and each LineItem has an amount field. I would like to get the grand total of a specific Order. Is it a good idea to add a 'total' column in the 'orders' table and update it every time a line_item is created/updated/deleted?
on 2006-03-20 07:30
on 2006-03-20 09:11
http://wiki.rubyonrails.org/rails/pages/MagicFieldNames see Counter Cache section as one of the solutions