Django primary-secondary relationship top list

models.py

from __future__ import unicode_literals

from django.db import models


class Main(models.Model):

    name = models.TextField()


class Son(models.Model):

    name = models.TextField()
    date = models.DateTimeField(auto_now_add=True)
    main = models.ForeignKey(Main, related_name='sons')
    value = models.IntegerField()

query.py

from datetime import timedelta

from django.db.models import Avg, Case, FloatField, Value, When
from django.db.models.functions import Coalesce, Now

from models import *


queryset = Main.objects.all().annotate(
  avg=Coalesce(
    Avg(Case(When(sons__date__gt=Now() - timedelta(days=1),
                  then='sons__value'),
             default=Value(None),
             output_field=FloatField())),
    Value(0))).order_by('-avg').values('name', 'avg')