movie.php

<?php
class Movie extends AppModel {
    // ...
     var $hasOne = array(
        'Attachment' => array(
            'className' => 'Media.Attachment',
            'foreignKey' => 'foreign_key',
            'conditions' => array('Attachment.model' => 'Movie'),
            'dependent' => true,
     ));
    // ...
}
?>