num_rows() function does not work

Hello Community,

Following is a code example.

Code:

       $this->db->select('*');
       $this->db->distinct();
       $query = $this->db->get('products');
       /*does not work*/
       echo $query->num_rows(); // this line does not work
       echo count($query->result_array()); // this line works

If I print_r($query) then num_rows, then it shows empty.

Please guide.

Regards,
Sam