django orm, backward relations,

user_19812079 0
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I have models as,

class Invoice():

class Entry():
   invoice = models.ForeignKey(Invoice, on_delete=models.PROTECT, related_name='entries')
   amount = CurrencyField()

I have to calculate total amount for a invoice by backward relation

django-models
1 Answers

A CurrencyField [GitHub] stores a currency, like 'USD', not an amount of a given currency, so not 5 USD. You need a MoneyField to do this.

The modeling thus should look like:

from django.db import models
from djmoney.models.fields import MoneyField


class Invoice(models.Model):
    pass


class Entry(models.Model):
    invoice = models.ForeignKey(
        Invoice, on_delete=models.PROTECT, related_name='entries'
    )
    amount = MoneyField(max_digits=14, decimal_places=2, default_currency='USD')

You can sum up the currency of an invoice with:

from django.db.models import Sum

my_invoice.entries.aggregate(total=Sum('amount'))['total']

this will only work if the amounts all have the same currency.

user_675790
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