Access different serializer if a queryset is empty Django Rest Framework - django

Question

I don't think I am implementing this correctly, but I am trying to change the serializer used for a queryset based on a condition (if there are no venues in one queryset, switch to another serializer and just return list object). I'm not quite sure how to do this.
Here is the view
class SavedVenuesViewSet(viewsets.ModelViewSet):
serializer_class = UserVenueSerializer
def get_queryset(self):
list_id = self.request.GET.get('list_id', None)
user = self.request.user.id
print(user)
print(list_id)
print(type(list_id))
qs = UserVenue.objects.filter(user_list=int(float(list_id)))
if not qs:
print("EMPTY LIST") #this is where i try to switch serializer
serializer_class = UserListSerializer
return UserVenue.objects.filter(id=int(float(list_id)))
else:
return qs
Here are the relevant serializers:
class UserVenueSerializer(serializers.ModelSerializer):
venue = mapCafesSerializer()
class Meta:
model = UserVenue
fields = ['user', 'user_list', 'venue']
depth = 2
[...]
class UserListSerializer(serializers.ModelSerializer):
class Meta:
model = UserList
fields = ['id', 'user', 'list_name']
depth = 2
The traceback isn't throwing an error but it isn't doing what I am hoping:
1
45
<class 'str'>
EMPTY LIST
[29/Sep/2021 11:05:36] "GET /api/savedvenues/?list_id=45 HTTP/1.1" 200 2

Answer 1

This is the correct practice to change serializer class in ModelViewSet:
You have to override get_serializesr_class method:
class SavedVenuesViewSet(viewsets.ModelViewSet):
serializer_class = UserVenueSerializer
def get_serializer_class(self):
if not self.get_queryset(): # Check your conditions here
return UserListSerializer
else:
return UserVenueSerializer

Answer 2

You could remove serializer_class field from your view, and create get_serializer_class() method, that will contain the logic for choosing the serializer. Is the best practice.
But, you can also, do it in your get queryset.
First, remove serializer_class attribute from your view. Instead, set it inside your get_queryset method (with this.serializer_class);
def get_queryset(self):
list_id = self.request.GET.get('list_id', None)
qs = UserVenue.objects.filter(user_list=int(float(list_id)))
if not qs:
self.serializer_class = UserVenueSerializer
return UserVenue.objects.filter(id=int(float(list_id)))
else:
self.serializer_class = UserListSerializer
return qs
Don't forget use the self.serializer_class.