Page 305 - Beginning PHP 5.3

10

Preserving State With Query

Strings, Cookies, and

Sessions

Most of the PHP scripts you created in previous chapters are very much one - shot affairs. Each time
they run, they start with a “ clean slate ” of variables and other data. This is because each request
that a browser makes to a Web server is independent of any previous requests. When a Web server
receives a request to run a PHP script, it loads the script into its memory, runs it, then removes all
trace of it from memory.

However, most of the Web applications you use today have a need to store data between browser
requests. For example, a shopping cart needs to remember which items you have added to your
cart, and a forum application needs to remember your identity whenever you post a message in
the forum.
In other words, there is a need to preserve the current state of a user ’ s interaction with an
application from one request to the next.

You ’ ve already looked at a simple example of storing state in the previous chapter, when you used
hidden form fields to store previously entered form data across each step of a three - stage
registration form. Although filling in the registration form involved three separate browser
requests — and therefore three separate runs of the PHP script — the script was able to
“ remember ” the state of the registration process by storing it in the forms themselves.

Although this approach works perfectly well for simple cases, it has a few disadvantages. For
example, it ’ s a slow way to store large amounts of data, because all the data has to be ferried
backward and forward from browser to server during each request. What ’ s more, it ’ s pretty
insecure, because it ’ s almost trivial for a mischievous user to change the data stored in the form at
will. In addition, if you need to store large numbers of variables between requests, as well as
complex variables such as arrays and objects, the hidden form field approach can start to get quite
cumbersome.

9/21/09 9:05:06 AM
c10.indd 267 9/21/09 9:05:06 AM
c10.indd 267