safeExecuteSelect example

  protected function doSave(array $link) {
    $affected_menus = [];

    // Get the existing definition if it exists. This does not use     // self::loadFull() to avoid the unserialization of fields with 'serialize'     // equal to TRUE as defined in self::schemaDefinition(). The makes $original     // easier to compare with the return value of self::preSave().     $query = $this->connection->select($this->table, NULL, $this->options);
    $query->fields($this->table);
    $query->condition('id', $link['id']);
    $original = $this->safeExecuteSelect($query)->fetchAssoc();

    if ($original) {
      $link['mlid'] = $original['mlid'];
      $link['has_children'] = $original['has_children'];
      $affected_menus[$original['menu_name']] = $original['menu_name'];
      $fields = $this->preSave($link, $original);
      // If $link matches the $original data then exit early as there are no       // changes to make. Use array_diff_assoc() to check if they match because:       // - Some of the data types of the values are not the same. The values       // in $original are all strings because they have come from database but       // $fields contains typed values.