A Practical Approach to Object-Relational Mapping in PHP Page 8

The code for ArmedHippo is quite simple:

<?php
class ArmedHippo extends Hippo 
{
    var $num_mount_points;
    //Constructor
    function ArmedHippo() 
    {
        parent::Hippo();
        $this->addField('num_mount_points',
        new DataField(DataField::TYPE_NUMERIC(), true) );
    }
    //Load record from DB
    function load($id) 
    {
        parent::load($id);
        $this->num_mount_points = $this->getDBValue('num_mount_points');
    }
    //Save record to DB
    function save() 
    {
        $this->setDBValue('num_mount_points', $this->num_mount_points );
        parent::save();
    }
}
?>

The constructor calls Hippo’s constructor (line 5), then adds a new data field,
num_mount_points (line 6). ArmedHippo::load()
calls Hippo::load() (line 11), then extracts the value for
the field it manages (line 12). ArmedHippo::save()
stores the value for num_mount_points (line 16), then calls
Hippo::save() (line 17).

Now we’ve got what we wanted. ArmedHippo can be added without disturbing
Hippo. A weight property can be added to Hippo,
without requiring changes to ArmedHippo. StealthHippo
can inherit from ArmedHippo, with no changes to existing code. Further,
no calls to functions that perform application utility tasks appear in Hippo,
ArmedHippo, or StealthHippo. They are
centralized in BusinessBase.

BusinessBase starts like this:

<?php
class BusinessBase 
{
    var $table_name = null;
    var $record = null;
    var $_id_field = null;
}
?>

$table_name is, of course, the name of the RDB table for the class.
$record is an associative array describing each record in the table.
The array’s index is the name of a field in the table (e. g., id). The value in each array element
is a DataField object: