Django. Rest Framework. Nested relationships empty result - django

Question

Need some advice. I set up seralization. There are no errors. But at the output I get empty tags. I broke my head, what am I doing wrong?
models.py:
class kv(models.Model):
title = models.CharField(max_length=200)
price = models.IntegerField()
address = models.CharField(max_length=200)
property_type = models.CharField(choices=realty_type_choices_admin, default='kv',
max_length=200, blank=True)
country = models.CharField(default='Россия', max_length=200)
region = models.CharField(max_length=200)
state = models.CharField(choices=state_choices_admin, default='DGO', max_length=200, blank=True, null=True)
locality_name = models.CharField(max_length=200, blank=True, null=True)
address_xml = models.CharField(max_length=200, blank=True, null=True)
city = models.CharField(max_length=100, blank=True, null=True)
serializers.py
from rest_framework import serializers
from listings.models import kv
class kvSerializerLocation(serializers.ModelSerializer):
class Meta:
model = kv
fields = ['country', 'region', 'state', 'locality_name', 'address_xml', 'city']
class kvSerializer(serializers.ModelSerializer):
category = serializers.CharField(source='get_property_type_display')
url = serializers.CharField(source='get_absolute_url', read_only=True)
country = kvSerializerLocation()
class Meta:
model = kv
fields = ['title', 'price', 'address', 'category', 'url', 'country']
views.py
from listings.models import *
from rest_framework import viewsets
from rest_framework_xml.renderers import XMLRenderer
from .serializers import kvSerializer
class KvXMLRenderer(XMLRenderer):
root_tag_name = 'feed'
item_tag_name = 'offer'
def _to_xml(self, xml, data):
super()._to_xml(xml, data)
class kvViewSet(viewsets.ModelViewSet):
queryset = Kvartiry.objects.all().filter(is_published=True)
serializer_class = kvSerializer
renderer_classes = [KvXMLRenderer]
Result:
<country>
<state/>
<locality_name/>
<address_xml/>
<city/>
</country>
It’s strange. Tags are empty, there is no region tag at all
Thank!

Answer 1

I don't think your implemenration would work for country because its a field, and there is no way to map that country value to your kv instance which can be utilized by kvSerializerLocation. Instead use SerializerMethodField:
class kvSerializer(serializers.ModelSerializer): # please use PascalCase for defining class name
category = serializers.CharField(source='get_property_type_display')
url = serializers.CharField(source='get_absolute_url', read_only=True)
kv_country = serializers.SerializerMethodField()
class Meta:
model = kv
fields = ['title', 'price', 'address', 'category', 'url', 'kv_country']
def get_kv_country(self, obj):
return kvSerializerLocation(obj).data