private function loadLabels(): void
  {
    $tables = DataLayer::getLabelTables();
    foreach ($tables as $table)
    {
      $rows = DataLayer::getLabelsFromTable($table['table_name'], $table['id'], $table['label']);
      foreach ($rows as $row)
      {
        $this->labels[$row['label']] = $row['id'];
      }
    }
  }