/**
  * Get options for a specific field as string split by ;
  * @param int $field_id
  * @param string $ordered_by Extra query bit for reordering
  * @return string HTML string of options
  * @assert (0, '') === null
  */
 public function get_field_options_by_field_to_string($field_id, $ordered_by = null)
 {
     $field = new ExtraField($this->type);
     $field_info = $field->get($field_id);
     $options = self::get_field_options_by_field($field_id, false, $ordered_by);
     $elements = array();
     if (!empty($options)) {
         switch ($field_info['field_type']) {
             case ExtraField::FIELD_TYPE_DOUBLE_SELECT:
                 $html = ExtraField::extra_field_double_select_convert_array_to_string($options);
                 break;
             default:
                 foreach ($options as $option) {
                     $elements[] = $option['option_value'];
                 }
                 $html = implode(';', $elements);
                 break;
         }
         return $html;
     }
     return null;
 }