public function _real_escape( $data ) {
    if ( ! is_scalar( $data ) ) {
      return '';
    }

    if ( $this->dbh ) {
      $escaped = mysqli_real_escape_string( $this->dbh, $data );
    } else {
      $class = get_class( $this );

      wp_load_translations_early();
      /* translators: %s: Database access abstraction class, usually wpdb or a class extending wpdb. */
      _doing_it_wrong( $class, sprintf( __( '%s must set a database connection for use with escaping.' ), $class ), '3.6.0' );

      $escaped = addslashes( $data );
    }

    return $this->wpdb::add_placeholder_escape( $escaped );
  }