Codeigniter - Multiple Database Connections

This is default database :

$db['default'] = array(
    'dsn'   => '',
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => '',
    'database' => 'mydatabase',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => TRUE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

Add another database at the bottom of database.php file

$db['db_1'] = array(
    'dsn'   => '',
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => '',
    'database' => 'mysecond',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => TRUE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

Add another database at the bottom of database.php file

$db['db_2'] = array(
    'dsn'   => '',
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => '',
    'database' => 'mythird',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => TRUE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

<?php
    class Your_model extends CI_Model {
        function __construct(){
            parent::__construct();
            //load our second db and put in $db1
            $this->db1 = $this->load->database('db_1', TRUE);
            //load our another db and put in $db2 
            $this->db2 = $this->load->database('db_2', TRUE);
        }

        public function getseconddbtabledata(){
            $query = $this->db1->get('db1_tablename');
            return $query->result(); 
        }
        public function getthirddbtabledata(){ 
           $query = $this->db2->get('db2_tablename'); 
           return $query->result(); 
        }

    }
?>