Check constraint on django - django

Question

I have two models
class Order(models.Model):
ord_number:str
ord_date: date
ord_ref: str Null=True
ord_qty: Decimal
ord_desc: str
timestamp: datetime
created: datetime
Class OrderLines(models.Model):
order: FK(Order)
driver: FK(Driver)
truck: FK(Truck)
ord_qty: Decimal
loaded_quantity: Decimal
loading_date: date
My schemas on posting will be like this
OrderCreateBase = create_schema(Order, exclude=("id", "timestmap", "created"))
OrderLineCreateBase = create_schema(OrderLines, exclude=("id))
class OrderCreateSchema(OrderCreateBase):
order_lines = List[OrderLineCreateBase]
Json data to be used on creating like this
"ord_number: "AB123",
"order_date: Date(01/01/2021),
"ord_ref" Null,
"ord_qty": Decimal("10_000"),
"ord_desc" "Sample Order",
"order_lines"[
{"order_id": 1,
"driver_id: 23,
"truck_id": 12,
"ord_qty": Decimal("10_000"),
"loaded_quantity": Decimal("8_000") <----#,
"loading_date": Date(01/01/2021)},
{"order_id": 1,
"driver_id: 13,
"truck_id": 17,
"ord_qty": Decimal("10_000"),
"loaded_quantity": Decimal("9_000") <----#,
"loading_date": Date(01/01/2021)}]
}
I want check constraint that will ensure total loaded quantity(loaded_quantity) per order will be <= to ordered_quantity (ord_qty)
currently my create endpoint is like this
#router.post(
"/ilr/{ilr_id}/instrunctions",
response={HTTPStatus.CREATED: Message, HTTPStatus.BAD_REQUEST: Message},
tags=["ilrs instructions"],
summary=_("create loading request instructions"),
description=_("API to create ilr instructions lines"),
url_name="create_ilr_instructions",
)
#transaction.atomic()
def create_ilr_instrunctions(request, ilr_id: int, payload: ILRLineCreateSchema):
data = payload.dict()
ilr = get_object_or_404(ILR, id=ilr_id, status=0)
data["request"] = ilr
data["order_date"] = ilr.ilr_date
# get existing lines total volume
total_volume = ILRLine.objects.filter(request=ilr).aggregate(total_volume=Sum("quantity"))
if ilr.quantity < total_volume.get("total_volume") + data.get("quantity"): <-----#
return HTTPStatus.BAD_REQUEST, {
"detail": [{"msg": f"Total loading quantities will be higher than ordered quantity"}]
}
try:
with transaction.atomic():
ILRLine.objects.create(**data)
.....
How can I force it on database level using check constraint? I don't want to override model save

Answer 1

You can try CheckConstraint.check
from django.db.models import CheckConstraint, Q, F
class OrderLines(models.Model):
...
class Meta:
constraints = [
CheckConstraint(
check=Q(loaded_quantity__lte=F('ord_qty')),
name='quantity_check'
)
]