使用代码点火器将会话保存到数据库时出错

Question

Controller_member

function login () {
        $data['content_view']='v_form_login.php';
        $this->load->view ('v_template',$data);

            $username = $this->input->post('username');
            $password =($this->input->post('password'));
            $login_status = $this->m_member->validasi ($username, $password);
                if ($login_status) {
                        $this->session->set_userdata('ses_username', $username);
                        $this->session->set_userdata('ses_login_status', $login_status);
                        redirect ('c_member/index');
                        }
    }

Model_member

public function validasi ($username, $password){
        $sql = "SELECT * FROM member WHERE username = '$username' AND password = '$password'";
        $result = $this->db->query($sql);
        $ketemu = $result->num_rows;

        if($ketemu>0){
            return true;
        }else{
            return false;
        }
    }

Model_slide

function delete_data($id){
$delete_date=$this->input->post('delete_date');
$query=$this->db->query("UPDATE slide SET delete_date=NOW() WHERE id='$id'");
}

我想从login_by是登录用户名的登录用户保存会话。