Django-禁用相关集中的重复项

Question

There is a class Order , SubOrder and class Product . I want to make sure that no Order object will contain multiple SubOrder objects with the same Product object.

class Order(TimeStampedModel):
    ....

class SubOrder(models.Model):
    order = models.ForeignKey('orders.Order', on_delete=models.CASCADE, related_name='suborders')
    product = models.ForeignKey('products.Product', on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField(verbose_name='Počet')

So if there were 3 products - A, B, C

I don't want allow one Order object to have multiple SubOrders with the same Product . For example Order[Suborder[A,12],Suborder[B,12],Suborder[B,5]] should raise ValidationError because there are two SubOrders with the same Product B .

Is it possible to do that on the model or database layer?

EDIT

I tried this:

def clean(self):
    neighbour_suborders = self.order.suborders.filter(product=self.product)
    if self.pk:
        neighbour_suborders = neighbour_suborders.exclude(pk=self.pk)
    if neighbour_suborders.exists():
        raise ValidationError("Takýto produkt už v objednávke existuje!")

But it allows to create such order in Django admin.

Answer 1

A unique constraint for order and product prevents saving more than one suborder for the same order and the same product:

class SubOrder(models.Model):
    class Meta:
        unique_together = ('order', 'product',)