Web Database Applications with PHP, and MySQL

The Shopping Cart Architecture

In Chapter 1, we introduced the requirements of the winestore shopping cart. A shopping cart is analogous to an incomplete order, in which each item in the cart is one or more bottles of a particular wine. Users can select any wine that is in stock to add to the cart, and wines in the cart can be purchased for up to one day after they have been added. The quantities of the wines can be updated by the user, and items in the cart can be deleted. In addition, the entire cart can be emptied.

We use the orders and items tables to manage the shopping cart. Alternative approaches include using only PHP sessions, JavaScript on the client, and database tables designed specifically for shopping cart management. The JavaScript approach is the least desirable because—as discussed in Chapter 7—JavaScript and the client are unreliable. PHP sessions are a practical, simple solution, but storing data in disk files results in unnecessary disk activity and relies on the operating system to manage I/O efficiently. The default disk file session store can be replaced with a MySQL session store, as discussed in Appendix D, but the approach is still likely to be less efficient than purpose-built database tables. Designing database tables specifically for shopping-cart management is a good solution, but—as we discuss next—it is unnecessary in the winestore application.

We use the orders and items tables as follows. When a user adds an item to his initially empty shopping ...