models.py

    teachers = models.ManyToManyField(
        "core.Person", related_name="extra_lessons_as_teacher", verbose_name=_("Teachers"),
    )
    room = models.ForeignKey(
        "Room", models.CASCADE, null=True, related_name="extra_lessons", verbose_name=_("Room"),
    )

    comment = models.CharField(verbose_name=_("Comment"), blank=True, null=True, max_length=255)

    def __str__(self):
        return f"{self.week}, {self.period}, {self.subject}"

    def get_groups(self) -> models.query.QuerySet:
        """Get groups relation."""
        return self.groups

    def get_teachers(self) -> models.query.QuerySet:
        """Get teachers relation."""
        return self.teachers

    def get_subject(self) -> Subject:
        """Get subject."""
        return self.subject

    class Meta:
        verbose_name = _("Extra lesson")
        verbose_name_plural = _("Extra lessons")


class ChronosGlobalPermissions(ExtensibleModel):
    class Meta:
        managed = False
        permissions = (
            ("view_all_timetables", _("Can view all timetables")),
            ("view_timetable_overview", _("Can view timetable overview")),
            ("view_lessons_day", _("Can view all lessons per day")),
        )