Forum_Structure.php

<?php
class Forum_Structure extends NotORM_Structure_Convention {
    function getReferencedTable($name, $table) {
        switch ($name) {
            case 'userFrom':
            case 'userTo':
                return parent::getReferencedTable('user', $table);
        }
        return parent::getReferencedTable($name, $table);
    }
}

$db = new NotORM($connection, new Forum_Structure);
?>