I'm working on a shopping cart application and I've run into a design
I have a field in the cart_lines table called total_price. That field
is really just a calculated field based on qty and unit_price. If
either of those values change, total_price should also be updated.
The way that makes the most sense to me is to write a method called
total_price that defines how it should be calculated rather than
modify the value directly from both the qty= and unit_price= methods.
The problem is, I want that value stamped in the database so I can use
it as a condition or sort field in queries.
I've written the following code (which works fine) that loops through
the object's attributes, checks to see if a method exists with the
same name, and updates the value if it's different:
class CartLine < ActiveRecord::Base
qty * unit_price
attributes.each do |attribute_name, attribute_value|
if respond_to_without_attributes? attribute_name
method_value = send(attribute_name)
send(attribute_name + "=", method_value) if method_value !=
That's fine and it works well but I'm wondering if I'm missing
something or there's a simpler way to handle this since I'm going to
have to reuse that code all over the place. If not, I could just
refactor it to a plugin but I'd be surprised since it sounds like it
would be a common situation.
How would you handle this? Any ideas or insight would be appreciated.