require_once 'DataObject.php'; class User extends DataObject { public $id; public $name; function comments() { return $this->count_rel('Comment', 'user_id'); } } class Comment extends DataObject { public $id; public $user_id; public $comment; } $user = new User(); $user->id = 1; $user->name = 'John Doe'; echo $user->comments(); // Output: 3In this example, we have a `User` class and a `Comment` class, with a one-to-many relationship between users and comments. The `comments` method in the `User` class uses the `count_rel` method to count the number of comments associated with that user. This example code uses the PEAR package `DB_DataObject`, which provides a set of classes for interacting with databases in an object-oriented way.