Codeigniter Active Record select on multiple databases - mysql

Question

I need some help to figure out how to make a select from tables in multiple databases using Active Record in Codeigniter.
In details: I have two database; in the first one there is a table named users with all details about user (first name, last name and so on); in the second database there is a table named credit where there are credit info about each user; the user_id is the key that links the tables.
In the contruct Model I have:
public function __construct()
{
parent::__construct();
$this->rci_db = $this->load->database('dev', TRUE);
}
The query to select the data is:
$this->db->select ("
$this->t_users.user_id,
$this->t_users.username,
$this->t_users.first_name,
$this->t_users.last_name,
$this->t_users.email,
$this->t_users.lastlogin,
$this->t_contributers.user_id AS credit
");
$this->db->from($this->t_users);
$this->db->join($this->rci_db.$this->t_contributers, "$this->t_contributers.user_id = $this->t_users.user_id");
The query doesn't work and I get the following error:
Error Number: 1146
Table 'gavsit_data.rci_imgcontributers' doesn't exist
SELECT `users`.`user_id`, `users`.`username`, `users`.`first_name`, `users`.`last_name`, `users`.`email`, `users`.`lastlogin`, `rci_imgcontributers`.`user_id` AS `credit` FROM `users` JOIN `rci_imgcontributers` ON `rci_imgcontributers`.`user_id` = `users`.`user_id` ORDER BY `id` ASC
Filename: models/adm/Users_model.php
Thanks a lot for any hint...I really don't know how to figure out this issue.
EDIT:
I've edited the code splitting the select query, the error has gone but I got no data from the second DB:
$this->db->select ("
$this->t_users.id,
$this->t_users.username,
$this->t_users.first_name,
$this->t_users.last_name,
$this->t_users.email,
$this->t_users.last_login,
$this->t_users.active
");
$this->rci_db->select("
$this->t_contributers.user_id,
$this->t_contributers.cbtid
");
$this->db->from($this->t_users);
$this->rci_db->join("$this->t_contributers", "$this->t_contributers.user_id = $this->db.$this->t_users.id", 'left');