[Python] Django prefetch_related on ForeignKey relation

I have this database setup:

class Profile(AbstractBaseUser, PermissionsMixin):
email = models.CharField(max_length=30, null=True, unique=True)
date_created = models.DateTimeField(auto_now=True) ...

class SubProfile(models.Model):
profile = models.OneToOneField(Profile, on_delete=models.CASCADE)
display_name = models.CharField(max_length=25) ...

class SubProfilePost(models.Model):
profile = models.ForeignKey(Profile, related_name='sub_profile_postings', on_delete=models.CASCADE)
title = models.CharField(max_length=20, null=False)
looking_for_date = models.DateTimeField(null=False)


How do I now fetch the SubProfiles, and prefetch the related SubProfilePosts?

I have tried doing this:

subprofile_queryset = SubProfile.objects \
select_related('profile') \
prefetch_related(
Prefetch('profile__sub_profile_postings', queryset=SubProfilePost.objects.only('id', 'looking_for_date')))


When I run the queryset through my serializers:

serializer = self.get_serializer(queryset, many=True)
return Response(serializer.data)


The data does not contain SubProfilePost(s). I can see the data if I directly access the obj.profile.sub_profile_postings.all().

I might be misunderstanding how prefetching works, or whether the data is annotated to the queryset when prefetching etc.

Can someone more experienced enlighten me if there is something wrong with my setup, or am I misunderstanding the whole concept.

Here are my serializers:

class ProfileSerializer(ModelSerializer):
class Meta:
model = Profile
fields = '__all__'
extra_kwargs = {
'password': {'write_only': True, 'required': False},
}


class SubProfilePostSerializer(ModelSerializer):
profile = ProfileSerializer()

class Meta:
model = SubProfilePost
fields = '__all__'


class SubProfileSerializer(ModelSerializer):
sub_profile_postings = SubProfilePostSerializer(many=True, read_only=True)

class Meta:
model = SubProfile
fields = [
'id',
'profile',
'display_name',
'sub_profile_postings', # Prefetched field
]

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