how to check username exit or not two different table in djnago rest framework

Question

while register new user in Tempdriver table need to varify username already exist or not in tempdriver table and appuser table, if check tempdriver table username its working but if i check appuser table getting error, pls someone help me out.

models.py- add models Tempdriver and Appuser

class Tempdriver(BaseModel):
    name = models.CharField(max_length=255)
    username = models.CharField(max_length=20,unique=True,null=True, blank=True)
    mobile = models.CharField(max_length=20,unique=True,null=True, blank=True)
    password = models.CharField(max_length=100)

class AppUser(BaseModel):
    username = models.CharField(max_length=50)

seriliazers.py

class TempDriverUserSerializer(serializers.ModelSerializer):
    class Meta:
        model=Tempdriver
        fields=('username','mobile')
    def validate(self,username):       
        user=Tempdriver.objects.filter(username=username)
        user_exists = AppUser.objects.filter(username=username)
        if  user.exists() and user_exists.exists():
            raise serializers.ValidationError("UserName already exists")
        
    def validate_mobile(self, mobile):
        mobile=Tempdriver.objects.filter(mobile=mobile)
        if mobile.exists():
            raise serializers.ValidationError("Mobile Number already exists")

views.py

class Tempuserapi(APIView):
 
    parser_classes=(MultiPartParser,FormParser)
    def post(self, request, format=None):
        serializer = TempDriverUserSerializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=HTTP_200_OK)
        else:
            return Response(serializer.errors, status= HTTP_200_OK)

trace report

ERROR Internal Server Error: /api/tempusercheck/
Traceback (most recent call last):
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\django\core\handlers\exception.py", line 34, in inner   
    response = get_response(request)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\django\views\generic\base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\rest_framework\views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\rest_framework\views.py", line 469, in handle_exception 
    self.raise_uncaught_exception(exc)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\rest_framework\views.py", line 480, in raise_uncaught_exception
    raise exc
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\rest_framework\views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "E:\10dec_everestfleet\everest_jarvis\api\views.py", line 632, in post
    if serializer.is_valid():
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\rest_framework\serializers.py", line 220, in is_valid   
    self._validated_data = self.run_validation(self.initial_data)
  File "E:\10dec_everestfleet\everest_jarvis\env\lib\site-packages\rest_framework\serializers.py", line 423, in run_validation
    assert value is not None, '.validate() should return the validated data'
AssertionError: .validate() should return the validated data
ERROR "POST /api/tempusercheck/ HTTP/1.1" 500 20285

Answer 1

def validate_username(self,value):
        data = self.get_initial()
        username = data.get('username')
        tempdriver = Tempdriver.objects.filter(username=username).exists()
        appuser = AppUser.objects.filter(username=username).exists()
        if tempdriver :
            raise serializers.ValidationError("Username already exists")
        if appuser:
            raise serializers.ValidationError("Username already exists")
        return value