Can I get this result of PostgreSQL query using Django ORM? - django

Question

I am having trouble with django ORM.
I want to get the data which I can get using PostgreSQL and raw sql query in views. But is there any solution to achieve this using Django ORM.
Here is my models
class Invoice(models.Model):
class PaymentMode(models.TextChoices):
Cash = 0, _('CASH')
Credit = 1, _('CREDIT')
class PaymentStatus(models.TextChoices):
Paid = 0, _('PAID')
Pending = 1, _('PENDING')
total_amount = models.IntegerField()
payment_mode = models.CharField(choices=PaymentMode.choices,
max_length=20,
default=PaymentMode.Credit)
payment_status = models.CharField(choices=PaymentStatus.choices,
default=PaymentStatus.Pending,
max_length=15)
print_date = models.DateField(default=now)
invoice_date = models.DateField(default=now)
created_by = models.ForeignKey(User, on_delete=models.DO_NOTHING)
customer = models.ForeignKey(Customer, on_delete=models.DO_NOTHING)
class Payment(models.Model):
class PaymentMethod(models.TextChoices):
Cash = 0, _('CASH')
Cheque = 1, _('CHEQUE')
OnlineTransfer = 2, _('WEB_TRANSFER')
Other = 3, _('OTHER')
invoice = models.ForeignKey(Invoice,
on_delete=models.DO_NOTHING,
default=0)
amount = models.IntegerField()
date = models.DateField(default=now)
recieved_by = models.CharField(max_length=150)
payment_method = models.CharField(choices=PaymentMethod.choices,
default=PaymentMethod.Cash,
max_length=20)
and here is my PostgreSQL query
SELECT
A.id ,
A.total_amount ,
A.payment_mode,
A.payment_status,
A.print_date,
A.invoice_date,
A.created_by_id,
A.customer_id,
coalesce(SUM(P.amount), 0) AS "paid",
(A.total_amount - coalesce(SUM(P.amount), 0)) As "remaining"
FROM
public."Invoicing_invoice" as A
LEFT JOIN public."Invoicing_payment" as P
ON P.invoice_id = A.id
GROUP BY A.id

Answer 1

You can annotate with:
from django.db.models import F, Sum, Value
from django.db.models.functions import Coalesce
Invoice.objects.annotate(
paid=Coalesce(Sum(payment__amount), Value(0)),
remaining=F('total_amount') - Coalesce(Sum(payment__amount), Value(0))
)
The Invoices that arise from this queryset will have two extra attribute .paid and .remaining with the paid and remaining amount of the invoice.