Nested serializer with optional field raising KeyError - django

Question

I have two serializers, first one (a bit simplified):
class FilterSerializer(serializers.Serializer):
brand = serializers.PrimaryKeyRelatedField(
queryset=org_models.Brand.objects, many=False,
error_messages={'does_not_exist': org_consts.BRAND_NOT_EXIST}
)
country = serializers.PrimaryKeyRelatedField(
queryset=org_models.Country.objects, many=False,
error_messages={'does_not_exist': org_consts.COUNTRY_NOT_EXIST}
)
level = serializers.PrimaryKeyRelatedField(
queryset=org_models.Level.objects, many=False, required=False,
error_messages={'does_not_exist': org_consts.DISTRICT_NOT_EXIST}
)
class Meta:
fields = ('brand', 'country', 'level')
and second:
class PeopleReportSerializer(serializers.Serializer):
filters = FilterSerializer(many=True)
start_date = serializers.DateField(required=False)
end_date = serializers.DateField(required=False)
class Meta:
fields = ('filters', 'start_date', 'end_date')
def validate(self, data):
"""Check if end_date occurs after start_date.
"""
if data.get('start_date') and data.get('end_date'):
if data['start_date'] > data['end_date']:
raise serializers.ValidationError(constants.INVALID_START_DATE)
return data
I've removed some fields for clarity.
So basically all I want from this serializer is validation if objects with posted ID exist in the database. On GET I would like it to return some data depending on request.user but that's another case.
So now in my view I'm doing something like this:
class PeopleReportView(ReportsPermissionMixin, views.APIView):
serializer_class = PeopleReportSerializer
task = staticmethod(people_report) # celery task, creates reports
def get(self, request):
# TODO: depending on request.user return initial data such as:
# country / brand / district and so on
return Response()
def post(self, request):
serializer = self.serializer_class(data=request.data)
if serializer.is_valid(raise_exception=True):
task = self.task.apply_async(kwargs=serializer.data)
return Response({'task_id': task.id})
my problem is that when I post data without level field (which is NOT a required field) I get KeyError: 'level'. FilterSerializer works fine, but when it's nested I'm getting this error. Apparently I was wrong, my test wasn't testing data property, only is_valid method.

Answer 1

Try using the allow_null flag instead:
level = serializers.PrimaryKeyRelatedField(
queryset=org_models.Level.objects, many=False, allow_null=True,
error_messages={'does_not_exist': org_consts.DISTRICT_NOT_EXIST}
)
instead of:
level = serializers.PrimaryKeyRelatedField(
queryset=org_models.Level.objects, many=False, required=False,
error_messages={'does_not_exist': org_consts.DISTRICT_NOT_EXIST}
)
See here for more information

Answer 2

Even though PrimaryKeyRelatedField is a Field it doesn't work the same way when initialized with required=False. Just like Remi wrote the only way that is supported in current version of DRF (3.5.X) for read/write fields is to allow_null on these fields (besides using some strange workarounds).
API has to send an empty field, and in object representation i.e. Serializer.data this fields will have a None value. Since in my case I mustn't had None values I modified Serialzier.to_representation method like so:
def to_representation(self, instance):
"""Excludes fields with None value from representation
"""
ret = super().to_representation(instance)
return {field: value for (field, value) in ret.items()
if value is not None}