Specifications

We’ll also need to add some information to our existing database about shipping addresses,
payment details, and so on.
We already know how to build an interface to a MySQL database using PHP, so this part of the
solution should be pretty easy.
Tracking a User’s Purchases While She Shops
There are two basic ways we can track a user’s purchases while she shops. One is to put her
selections into our database, and the other is to use a session variable.
Using a session variable to track selections from page to page will be easier to write as it will
not require us to constantly query the database for this information. It will also avoid the situa-
tion where we end up with a lot of junk data in the database from users who are just browsing
and change their minds.
We need, therefore, to design a session variable or set of variables to store a user’s selections.
When a user finishes shopping and pays for her purchases, we will put this information in our
database as a record of the transaction.
We can also use this data to give a summary of the current state of the cart in one corner of the
page, so a user knows at any given time how much she is planning to spend.
Payment
In this project, we will add up the user’s order and take the delivery details. We will not actu-
ally process payments. Many, many payment systems are available, and the implementation for
each one is different. We will write a dummy function that can be replaced with an interface to
your chosen system.
Payment systems are generally sold in more specific geographic areas than this book. The way
the different real-time processing interfaces works is generally similar. You will need to orga-
nize a merchant account with a bank for the cards you want to accept. Your payment system
provider will specify what parameters you will need to pass to their system.
The payment system will transmit your data to a bank, and return a success code of one of
many different types of error codes. In exchange for passing on your data, the payment gate-
way will charge you a setup or annual fee, and a fee based on the number or value of your
transactions. Some providers even charge for declined transactions.
Your chosen payment system will need information from the customer (such as a credit card
number), identifying information from you (to specify which merchant account is to be cred-
ited), and the total amount of the transaction.
Building a Shopping Cart
C
HAPTER 25
25
B
UILDING A
SHOPPING CART
541
31 7842 CH25 3/6/01 3:38 PM Page 541