trait ViewsSqlQueryGetConnectionTrait in Range 8

trait ViewsSqlQueryGetConnectionTrait {

  /**
   * Gets the database connection to use for the view.
   *
   * The returned database connection does not have to be the default database
   * connection. It can also be to another database connection when the view is
   * to an external database or a replica database.
   *
   * @return \Drupal\Core\Database\Connection
   *   The database connection to be used for the query.
   */
  protected function getDatabaseConnection(Sql $query) {

    // Call the getConnection() method directly if exists (D9.1+).
    if (method_exists($query, 'getConnection')) {
      return $query
        ->getConnection();
    }
    else {

      // Set the replica target if the replica option is set for the view.
      $target = empty($query->options['replica']) ? 'default' : 'replica';

      // Use an external database when the view configured to.
      $key = $query->view->base_database ?? 'default';
      return Database::getConnection($target, $key);
    }
  }

}