check if certain value exist in table codeigniter

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PHP

CodeIgniter

i have table like that
note that id is auto increament

and the function not using passing id to check it so i need to check the value of ad_code and ad_image without using id
____________________________________________________
id type ad_code ad_image
______________________________________________________


i want to check if ad_code value exist update it else insert it also if ad_image exist update it else insert it


i tried

$data['type']=$type;
             $data['ad_image']=$image_link;
             $data['ad_code']=$code;

             if($this->site_adds_model->count_all()>0)
             {
               $this->site_adds_model->update_by($data);
               $this->session->set_flashdata('message', 'adds updated in database');
               redirect(current_url(), 'refresh');
             }
            else
            {
               $this->site_adds_model->insert($data);
               $this->session->set_flashdata('message', 'adds inserted in database');
               redirect(current_url(), 'refresh');
            }

note that the table has only one raw any help