How to get additional data ' id' from <select> options

[eluser]Jan_1[/eluser]
Hello! As I've read in the User Guide:

If you would like the opening <select> to contain additional data, like an id attribute, you can pass it as a string in the fourth parameter:
$js = 'id="shirts" onChange="some_function();"';

echo form_dropdown('shirts', $options, 'large', $js);

So I did, but I dont know how to grab the 'additional data' to write it in the database.
Could somebody give me hint or a link to a post (which I haven't found).
THANK YOU!!!

View

Code:

<?php echo form_open_multipart('kasse/save_ks_buchung'); ?>
    <tr>
      <td>&lt;input type='text' name='ks_datum' value="&lt;?php echo mdate($datestring, $time); ?&gt;" size='12'/&gt;&lt;/td>
      <td>&lt;input type='text' name='ks_text' value="" size='30'/&gt;&lt;/td>
      <td>&lt;input type='text' name='ks_betrag' value="" size='8'/&gt;&lt;/td>
      <td>&lt;?php echo form_dropdown('ks_art', $options_ks_art, 'Sonstiges');?&gt;</td>
/*->*/<td>&lt;?php echo form_dropdown('ks_auslage',$name_ks_auslage,$selected_ks_auslage,$id_ks_auslage);?&gt;</td>
      <td>&lt;input type='hidden' name='wg_id' value='&lt;?=$wg[0]-&gt;wg_id?&gt;'/>
          &lt;input type='submit' value='speichern'/&gt;&lt;/td>
    </tr>
  &lt;/form&gt;

Controller:

Code:

function show()
    {
        $this->load->helper('date');
        $this->load->helper('form');
        $this->load->model('kasse/kasse_model');
        $this->load->model('standard_model');
        $data['wg']= $this->standard_model->get_wg_id();
        $data['options_ks_art'] = $this->kasse_model->get_ks_art();
        $data['name_ks_auslage'] = $this->kasse_model->get_ks_auslage_name();
        $data['selected_ks_auslage'] = $this->kasse_model->get_ks_auslage_wg();
        $data['id_ks_auslage'] = $this->kasse_model->get_ks_auslage_id();
        $data['ks_buchungen'] = $this->kasse_model->get_my_ks_buchungen();
        
        $dataform['heading'] = 'Unsere WG-Kasse';
        $dataform['page'] = $this->config->item('FAL_template_dir').'template/kasse/meine_kasse_temp';

        $this->load->vars($data);
        $this->load->view($this->_container, $dataform);
    }

    function save_ks_buchung()
    {
        $this->load->model('kasse/kasse_model');
        $this->load->helper('form');
        $this->load->plugin('js_calendar');
        $this->kasse_model->insert_ks_buchung();
        redirect('/kasse/show', 'refresh');
  }

Model:

Code:

function get_ks_auslage_name()
    {
      $wg_id = x; // done by db-query, if've just cut it here (works)  
      $data = array();
      $this->db->select('user_name');
      $this->db->where('wg_id',$wg_id, FALSE);
      $this->db->where_not_in('user_id', $this->db_session->userdata('id'), False);
      $query = $this->db->get('wg_member');
          foreach ($query->result() as $row)
                  {$data[$row->user_name] = $row->user_name; }
      return $data;
     }

  function get_ks_auslage_id()
    {
      $wg_id = x; // done by db-query, if've just cut it here (works)
      $data = array();
      $this->db->select('id');
      $this->db->where('wg_id',$wg_id, FALSE);
      $this->db->where_not_in('user_id', $this->db_session->userdata('id'), False);
      $query = $this->db->get('wg_member');
          foreach ($query->result() as $row)
                  {$data[$row->id] = $row->id;}
      return $data;
     }
    
  function get_ks_auslage_wg()
    {
      $wg_id = x; // done by db-query, if've just cut it here (works)
      $data = array();
      $this->db->select('user_name');
      $this->db->where('wg_id',$wg_id, FALSE);
      $this->db->like('user_name','WG', FALSE);
      $query = $this->db->get('wg_member');
          foreach ($query->result() as $row)
                  {$data[$row->user_name] = $row->user_name;}
      return $data;
     }

  function insert_ks_buchung()
    {
      extract($_POST);
      $data = array(
                    'geloescht' => '0',
                    'wg_id' => $wg_id,
                    'user_name' => getUserName(),
                    'user_id' => $this->db_session->userdata('id'),
                    'ks_datum' => $ks_datum,
                    'ks_text' => $ks_text,
                    'ks_betrag' => $ks_betrag,
                    'ks_art' => $ks_art,
                    'change_user' => '0',
                    'ks_auslage' => $ks_auslage,
                    'id_ks_auslage' => $id_ks_auslage  // how could I pass it down here from the VIEW??
                   );
      $this->db->insert('ks_buchung', $data);
    }