Page 398 - Beginning PHP 5.3

Part III: Using PHP in Practice
Making a Connection

To make a connection to a MySQL database in your PHP script, all you need to do is create a new PDO
object. When you create the object, you pass in three arguments: the DSN, which describes the database
to connect to; the username of the user you want to connect as; and the user ’ s password. The returned
PDO object serves as your script ’ s connection to the database:

$conn = new PDO( $dsn, $username, $password );

A DSN , or Database Source Name, is simply a string that describes attributes of the connection such as
the type of database system, the location of the database, and the database name. For example, the
following DSN can be used to connect to a MySQL database called mydatabase running on the same
machine as the PHP engine:

$dsn = “mysql:host=localhost;dbname=mydatabase”;

If host isn ’ t specified, localhost is assumed.
So, putting it all together, you could connect to your mydatabase database as follows (replacing mypass
with your real root password of course):
$dsn = “mysql:dbname=mydatabase”;
$username = “root”;
$password = “mypass”;
$conn = new PDO( $dsn, $username, $password );
When you ’ ve finished with the connection, you should close it so that it ’ s freed up for other scripts to
use. Although the PHP engine usually closes connections when a script finishes, it ’ s a good idea to close
the connection explicitly to be on the safe side.

To close the connection, just assign null to your connection variable. This effectively destroys the PDO
object, and therefore the connection:

$conn = null;

Handling Errors

Database errors can be notoriously difficult to track down and deal with. One of the nice things about
PDO is that you can get it to return MySQL errors in the form of highly descriptive PDOException
objects. You can then use the PHP keywords try and catch to handle these exceptions easily and deal
with them appropriately.
Exceptions are covered fully in Chapter 20, so you just learn the basics here.

To set PDO to raise exceptions whenever database errors occur, you use the PDO::SetAttribute
method to set your PDO object ’ s error mode, as follows:

$conn = new PDO( $dsn, $username, $password );
$conn- > setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

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