How do I get the autoincremented ID of the latest inserted row.

My code:

PHP Code:

    $this->db->simpleQuery('Use D'.$id);
    $this->db->table('drawings')->insert(array("name"=>$fname));
    return $this->db->insertID(); 


This returns a model object, but I need the number of the ID.
if I use

PHP Code:

$this->db->insert_id(); 


I get an error which says that insert_id() is an undefined method.

Code:

+----------+--------------+------+-----+---------------------+----------------+
| Field    | Type        | Null | Key | Default            | Extra          |
+----------+--------------+------+-----+---------------------+----------------+
| id      | int(9)      | NO  | PRI | NULL                | auto_increment |
| name    | varchar(255) | YES  |    | NULL                |                |
| revision | char(3)      | NO  |    | NULL                |                |
| date    | timestamp    | NO  |    | current_timestamp() |                |
+----------+--------------+------+-----+---------------------+----------------+

~ Dave