How to update joined tables

I've been searching for an answer to this, but evidently the working solution for v2 doesn't work in v3.

Code:

$this->db->set('a.firstname', 'Pekka');
$this->db->set('a.lastname', 'Kuronen');
$this->db->set('b.companyname', 'Suomi Oy');
$this->db->set('b.companyaddress', 'Mannerheimtie 123, Helsinki Suomi');

$this->db->where('a.id', 1);
$this->db->where('a.id = b.id');
$this->db->update('table as a, table2 as b');

That code came from here - http://tinyurl.com/jjarn8r

Does anyone have a working solution please?

Yours Roy
Bee Creative Web Design
www.bcwd.ltd.uk