models.py 文件源码

def renew(self):
        """Renew lendable.

        If renewals are available update the due_on date by adding
        another period equal to lending_period_in_days.

        If no renewals available raise error and display message to user.
        """
        if self.renewals > 0:
            self.renewals -= 1
            self.due_on = self.due_on + timedelta(self.lending_period_in_days)
        else:
            raise ValidationError(
                _("No more renewals are available for this item.")
            )
        return self.save()