如何获取查询集而不是字典 django 聚合

Question

i'm using this queryset for my requirements

invoices = Invoice.objects.aggregate(total_amount=Sum('order__order_items__amount'),number_of_invoices=Count('pk', distinct=True))

which returns dict--->

{'total_amount': Decimal('17700.00'), 'number_of_invoices': 2}

but I want queryset how can i do that.. Thanks for any help

Answer 1

This is what aggregate do:)

You can add a DecimalField to Invoice model, that aggregates total_amount during before every save. I suggest signals for that.

apps.py

class YourAppConfig(AppConfig):
    ...

    def ready(self):
        from . import signals

signals.py

from django.db.models.signals import pre_save
from django.dispatch import receiver

from .models import Invoice

@receiver(pre_save, sender=Invoice)
def total_amount_aggregation(sender, instance, *args, **kwargs):
    instance.total_amount = # aggregate desired amount here

You have to set similar signals for your Order , so if you change Order object, the related Invoice object will be recalculated.

After that QuerySet will stay as QuerySet and every object will have always caclulated field.

Answer 2

Instead of using .aggregate(...) use .annotate(...) this will return a QuerySet with given expression

from django.db.models import Sum, Count

invoices = Invoice.objects.annotate(
            total_amount=Sum('order__order_items__amount'),
            number_of_invoices=Count('pk', distinct=True)
           )

then to getSum(...) &Count(...) of field do like this invoices[0].total_amount__sum & invoices[0].number_of_invoices__count