How to update a JOINed tables using Codeigniter's Active Record?

Codeigniter active record doesn't allow to update a joined tables. 
After trying various method and searching the solution, I have found the following solution which does the exactly same thing i.e. update the multiple join tables. By using following method, you can update multiple table using codeigniter active record.

$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');