# тут происходит сама логика очередей, учитывается привязка к другой моделе
class OrderField(models.PositiveIntegerField):
    def __init__(self, for_fields=None, *args, **kwargs):
        self.for_fields = for_fields
        super(OrderField, self).__init__(*args, **kwargs)

    def pre_save(self, model_instance, add):
        if getattr(model_instance, self.attname) is None:
            # no current value
            try:
                qs = self.model.objects.all()
                if self.for_fields:
                    # filter by objects with the same field values
                    # for the fields in "for_fields"
                    query = {field: getattr(model_instance, field) for field in self.for_fields}
                    qs = qs.filter(**query)
                # get the order of the last item
                last_item = qs.latest(self.attname)
                value = last_item.queue_number + 1
            except ObjectDoesNotExist:
                value = 1
            setattr(model_instance, self.attname, value)
            return value
        else:
            return super(OrderField,
                         self).pre_save(model_instance, add)

class Module(TimeLearningMixin, ByQueueNumberMixin, models.Model):
    name = models.CharField(max_length=200)
    course = models.ForeignKey(Course, on_delete=models.CASCADE, related_name='modules', default=None)

    queue_number = OrderField(blank=True, for_fields=['course'])

def delete(self, *args, **kwargs):
    try:
        n_boock = NumberBooks.objects.get(school=self.school, edition=self.edition)
        val = self.type_of_movement * self.quantity
        n_boock.in_warehouse -= val
        n_boock.save()
    except:
        pass
    super(IncomeExpense, self).delete(*args, **kwargs)