Applying a Django FilterSet to an Annotated QuerySet?

Question

I'm trying to apply a filter to an annotated queryset, like is done here: https://docs.djangoproject.com/en/2.0/topics/db/aggregation/#filtering-on-annotations

Similar to the snippet below, I'd like to make that highly_rated piece a FilterSet that picks up the request parameters

highly_rated = Count('books', filter=Q(books__rating__gte=7))
Author.objects.annotate(num_books=Count('books'), highly_rated_books=highly_rated)

I'd like to make that highly_rated piece a FilterSet that picks up the request queries. Something like:

class MainFilter(FilterSet):
    class Meta:
        model = Author
        fields = {
            author: ['in', 'exact'],
            genre: ['in', 'exact']
        }

class AnnotatedFilter(FilterSet):
    class Meta:
        fields = {
            'books__rating': ['gt', 'lt' ],
        }

class MyView(ListApiView):
    filter_class = AuthorFilter

    def get_queryset(self):
        annotated_filter = AnnotatedFilter(request) # how do I set up another filter based on the request?
        Author.objects.annotate(num_books=Count('books'), FilterSet=annotated_filter) # how do I apply it to an annotated queryset?

All so I can query something like:

api/authors/?genre=Fantasy&books__rating__gt=5

Where one of the parameters executes against all the records and other params execute against the annotated part.

Any help is greatly appreciated. Thanks!

Answer 1

Change get_queryset() method to

def get_queryset(self):
    return Author.objects.annotate(num_books=Count('books')

and define that field in Filter class as

class AuthorFilter(FilterSet):
    num_books = filters.NumberFilter(name='num_books')
    class Meta:
        model = Author
        fields = ['num_books',]#other fields

then use the api as /api/end/point/authorlist/?num_books=10

EXAMPLE

models.py

from django.db import models


class Sample(models.Model):
    foo = models.IntegerField()
    bar = models.IntegerField()

views.py

from django.db.models import F
from django_filters import rest_framework as filters


class MySampleAPI(viewsets.ModelViewSet):
    filter_backends = (filters.DjangoFilterBackend,)
    filter_class = SampleFilterClass
    serializer_class = SampleSerializerClass

    def get_queryset(self):
        return Sample.objects.annotate(foo_bar_sum=F('foo') + F('bar'))

filters.py

from django_filters import rest_framework as filters


class SampleFilterClass(filters.FilterSet):
    sum = filters.NumberFilter(name='foo_bar_sum', lookup_expr='gte')

    class Meta:
        model = Sample
        fields = ['sum', ]