Error DB handle Codeigniter 3

==================================
= ../config/database.php
==================================
$db['default'] = array(
    'dsn'   => '',
    'hostname' => 'localhost',
    'username' => '<<USER_DB>>',
    'password' => '<<PASS_DB>>',
    'database' => '<<NAMA_DB>>',
    'dbdriver' => 'postgre',
    'dbprefix' => '',
    'pconnect' => FALSE,
    '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
);

=========================================
= index.php
=========================================
define('ENVIRONMENT', isset($_SERVER['CI_ENV']) ? $_SERVER['CI_ENV'] : 'production');

==========================================
= models untuk hapus record
==========================================
function hapus($item)
{
        $this->db->where($this->primary_key,$item);
        $this->db->delete($this->table_name);
}

=========================================
= controllers (fungsi delete)
=========================================
public function delete()
{
        $id = $this->input->post('id');
        $this->model_name->hapus($id);

        //gunakan fungsi error untuk mengambil error yang terjadi
        $error = $this->db->error();
        if ($error['message']=='') {
            $result = array('success'=>TRUE);
            echo json_encode($result);
        } else {
            $result = array('errorMsg' =>$error['message']);
            echo json_encode($result);
        }
}