private function _add_primary(array &$cfg): void
  {
    // Inserting a row without primary when primary is needed and no auto-increment
    if (
      !empty($cfg['primary']) &&
      empty($cfg['auto_increment']) &&
      (($idx = array_search($cfg['primary'], $cfg['fields'], true)) > -1) &&
      (count($cfg['values']) === (count($cfg['fields']) - 1))
    ){
      $val = false;
      switch ( $cfg['primary_type'] ){
        case 'int':
          $val = random_int(
            ceil(10 ** ($cfg['primary_length'] > 3 ? $cfg['primary_length'] - 3 : 1) / 2),
            ceil(10 ** ($cfg['primary_length'] > 3 ? $cfg['primary_length'] : 1) / 2)
          );
          break;
        case 'binary':
          if ( $cfg['primary_length'] === 16 ){
            x::log($cfg['tables'], 'add_options');
            $val = $this->get_uid();
            x::log($val, 'add_options');
          }
          break;
      }
      if ( $val ){
        array_splice($cfg['values'], $idx, 0, $val);
        $this->set_last_insert_id($val);
        x::log(['v' => $cfg['values'], 'f' => $cfg['fields']], 'add_options');
      }
    }
  }