In this chapter, we've covered the basic techniques for connecting to and reading data from a MySQL DBMS using PHP. In this section, we extend this to writing data.
Example 11-4 shows the
script that adds and removes gifts from
a guest's shopping list. The script uses the MySQL
library functions we discussed earlier. If the user-supplied
$action variable has the value
insert, an attempt is made to reserve the gift
with the value in
$present_id for the current
$action is set to
delete, an attempt is made to remove the gift from
the guest's shopping list. As discussed in the
previous section, the guest's
people_id is maintained in the
$user session variable.
The script first checks the status of the gift with the identifier
$present_id. If the gift is already reserved, the
current guest can't reserve it; this can happen if
another guest is using the application and beats the current guest to
it. Likewise, the script checks that the gift is reserved by the
current guest before actually unreserving it; this check should never
fail, unless the same user is logged in twice. Defensive programming,
or thinking through all the possibilities that can occur, is wise
when developing for the Web, since each script is independent, and
there are no time limits or controls in our application on when a
user can request a script.
Example 11-4. The action.php script reserves gifts or removes them from a shopping list
<?php // Add or remove a gift from ...