Order column desc in one query $data

Hi ,maybe this just simple question, but i don't have answer yet 

My query is this :
$data['employee'] = $this->m_data->get_data('employee')->result();

I want to order descending, i try this 
$data['employee'] = $this->m_data->get_data('employee')->order_by("employee_id desc")->result();
But it gave error like this :


Message: Call to undefined method CI_DB_mysqli_result::order_by()

How to fix the query ?

Hi ,maybe this just simple question, but i don't have answer yet 

My query is this :
$data['employee'] = $this->m_data->get_data('employee')->result();

I want to order descending, i try this 
$data['employee'] = $this->m_data->get_data('employee')->order_by("employee_id desc")->result();
But it gave error like this :


Message: Call to undefined method CI_DB_mysqli_result::order_by()

How to fix the query ?

Every method returns allows for chaning, except get and get_where which returns the result. Try to place order_by() before get_data()

Show the code for m_data->get_data()

Finally it works,i just changet the query sentence
$data['tbl_tamu'] = $this->db->query("SELECT * FROM tbl_tamu order by tbl_tamu_id desc")->result();