def save()

in server/store/models.py [0:0]


    def save(self, *args, **kwargs):
        if self.active:
            qs = type(self).objects.filter(active=True)
            if self.pk:
                qs = qs.exclude(pk=self.pk)
            qs.update(active=False)

        super(Product, self).save(*args, **kwargs)