python - get() returned more than one AccessToken -

i facing 2 issues here.

1) if user has not old token, new 1 should generated , logged in not happening so.

2)a newly created user when logs in gets 'you have multiple authentication backends configured , therefore must provide backend argument or set backend attribute on user.'

3)old user when trying login gets error of get() returned more 1 accesstoken -- returned 8!

expert might understand code

class userloginapi(apiview):     permission_classes = [allowany]     serializer_class = userloginserializer      def post(self, request, *args, **kwargs):         access_token = request.get.get('access_token')         data = request.data         print('data',data)         serializer = userloginserializer(data=data)         if serializer.is_valid(raise_exception=true):             new_data = serializer.data             if new_data:                 app = application.objects.get(name="foodie")                 try:                     user = user.objects.get(username=data['username'])                     print ('user',user)                 except objectdoesnotexist:                     return httpresponse("can't find user")                 else:                     try:                         access_token = accesstoken.objects.get(user=user)                     except objectdoesnotexist:                         return httpresponse('have not set token')                     else:                         access_token.delete()                 new_token = generate_token()                 print('new_token',new_token)                 accesstoken.objects.create(user=user, application=app, expires=datetime.now() + timedelta(days=365),token=new_token)                 print('aceess',accesstoken)                 login(request, user)             return response(new_data, status=status.http_200_ok)         return response(serializer.errors, status=status.http_400_bad_request) 

serializers.py

class userloginserializer(modelserializer):     username = charfield()     class meta:         model = user         fields = ['username', 'password']   class usercreateserializer(modelserializer):     class meta:         model = user         extra_kwargs = {"password": {"write_only": true}}       def create(self, validated_data):         user_obj = user(                 username = username,                 first_name = first_name,                 last_name = last_name,                 email = email             )         user_obj.set_password(password)         user_obj.save()         if user_obj:             expire_seconds = oauth2_settings.user_settings['access_token_expire_seconds']             scopes = oauth2_settings.user_settings['scopes']              application = application.objects.get(name="foodie")             expires = datetime.now() + timedelta(seconds=expire_seconds)             access_token = accesstoken.objects.create(user=user_obj,                                                      application=application,                                                     token = generate_token(),                                                     expires=expires,                                                      scope=scopes)         return validated_data