Page 427 - Beginning PHP 5.3

Chapter 13: Retrieving Data from MySQL with PHP
$conn = “”;
}
}

? >
So how does this class work? First of all, the script includes the config.php file so that it can access the
database configuration constants:

require_once “config.php”;

The PHP require_once() function imports another PHP script into the current script in a similar way to
require() , which you ’ ve used in previous chapters. The difference is that require_once() ensures that
the file is imported only once. This is important if you create a large application with lots of script files,
many of which need to include the same file, such as config.php . If you used require() , the PHP engine
would include config.php every time it encountered the require() function call, resulting in multiple
copies of the config.php file being included in the application (with, needless to say, chaotic results).

Find out more about require_once() and related functions in Chapter 20.

Next, the class declares a protected $data array to hold the record ’ s data. The fact that it ’ s protected
means that the classes that derive from this class will be able to use it, but it ’ s still hidden from the
outside world (as most properties should be).
The first method, __construct() , is the class ’ s constructor. It ’ s called whenever a new object is created
based on a class that ’ s derived from this class. The constructor accepts an associative array of field names
and values ( $data ) and stores them in the protected $data array (assuming each field name exists in
$data ). In this way it ’ s possible for outside code to create fully populated data objects.
The getValue() method accepts a field name, then looks up that name in the object ’ s $data array. If
found, it returns its value. If the field name wasn ’ t found, the method halts execution with an error
message. getValue() enables outside code to access the data stored in the object.

getValueEncoded() is a convenience method that allows outside code to retrieve a field value that has
been passed through PHP ’ s htmlspecialchars() function. This function encodes markup characters
such as < and > as & lt; and & gt; . Not only is this required when generating XHTML markup, but it ’ s
also a good security measure that can help to reduce the risk of malicious markup making its way into
your Web page.

The final two protected functions allow classes to create a PDO connection to the database, as well as
destroy a database connection. connect() creates a new PDO object and returns it to the calling code.
Along the way, it sets a couple of useful attributes:

$conn- > setAttribute( PDO::ATTR_PERSISTENT, true );

$conn- > setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
Setting the PDO::ATTR_PERSISTENT attribute to true allows PHP to keep the MySQL connection open
for reuse by other parts of the application (or other applications). With this attribute set to false , which
is the default setting, a new MySQL connection is opened every time a new PDO object is created in the
application. Because setting up a new MySQL connection takes both time and resources, setting this
attribute to true can help to improve performance.

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