models.py

        if self.title:
            return self.title
        else:
            return _("Event {}".format(self.pk))

    class Meta:
        ordering = ["date_start"]
        indexes = [models.Index(fields=["period_from", "period_to", "date_start", "date_end"])]
        verbose_name = _("Event")
        verbose_name_plural = _("Events")