With your products on display, you can start actually allowing people to buy them. To do this, you're going to need to implement a shopping cart. If you want, you can refer back to the design of the shopping cart in Chapter 4, “The Sample Application Functional Requirements Document.”
A cart is essentially a container that you can put products into, with a few quirks. For example, putting a second copy of an item into a cart shouldn't make two entries; it should make a single item with a quantity of 2.
The cart has session persistence, like the customer. Unlike the customer object however, it doesn't get its contents from a database lookup. Eventually, when you get to filling and spilling content in Chapter 11