in addition to what @Thomas said you need to first perform an aggregated
sum on the payments model hence the need for ...
loan.payments_set.aggregrate(models.Sum('amount'))
the above returns the sum of all payment related to your loan instance from
which you can now subtract from loan.amount_to_pay
you can read this post for further
clarity
https://medium.com/@clemcy9/performing-aggregate-sum-in-postgresql-django-3472e5248bb3
On Friday, 7 July 2023 at 16:03:09 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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