Re: Calculations

Or, you can combine annotations and expressions to do something like this:

qs = LoanInformation.objects.annotate(outstanding=F("amount_to_pay") - Func(F("payments__amount"), function="SUM))

loan = qs.get(id=loan_id)

loan.outstanding

On Friday, July 7, 2023 at 4:03:09 PM UTC+1 Thomas Couch wrote:

Hi Abdou, have a look at aggregation (https://docs.djangoproject.com/en/4.2/topics/db/aggregation/)

In this case I think you'll want something like:

```

from django.db.models import Sum

# Where loan = the LoanInformation instance you're interested in

outstanding_balance = loan.amount_to_pay - loan.payments_set.aggregate(Sum("amount"))

```

On Thursday, July 6, 2023 at 5:39:50 PM UTC+1 Abdou KARAMBIZI wrote:

class LoanInformation(models.Model):
    id = models.AutoField(primary_key=True)
    customer = models.ForeignKey(Customer,on_delete=models.CASCADE)
    amount_to_pay = models.IntegerField()
 
    def __str__ (self):
        return self.id

class Payments(models.Model):
    id = models.AutoField(primary_key = True)
    loan = models.ForeignKey(LoanInformation,on_delete=models.CASCADE)
    amount = models.IntegerField()
    paidon = models.DateField(auto_now=True)

    def __str__ (self):
        return self.id

I want to display the result of  "amount_to_pay - sum of amount"

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