Doctrine_RawSql自定义选择

I having problems to generate a doctrine_rawsql with a custom select.

This is my rawsql

$distance = glength(linestringfromwkb(linestring(asbinary(GeomFromText('POINT( FLOAT('30') FLOAT('-3')),asbinary({l.point})))) as distance

$q->select($distance)
                ->from('place p INNER JOIN location l ON p.location_id = l.id')
                ->addComponent('p', 'Place p')
                ->addComponent('l', 'p.Location l')

if I do a $q->getSql() the distance doesn't appears in the generated sql.

Any ideas? I am doing something wrong?

The problem seems to be solved now using Doctrine_Expression

$user = new User(); 
$user->username = 'jwage'; 
$user->updated_at = new Doctrine_Expression('NOW()'); 
$user->save();