serializer.py

class SessionHistoryCreateSerializer(DocumentSerializer):

    class Meta:
        model = SessionHistory
        fields = '__all__'

    # check date...
    def validate(self, data):
        data = super().validate(data)
       
        if data['start_date'] >= data['end_date']:
            raise ValidationError('start date must be behind end data')

    # check data usage....
    def validate_voucher_data_limit(self):
        data = self.validated_data
        voucher = data['voucher']
        user_sessions = SessionHistory.objects.filter(user=data['user'], voucher=voucher)
        data_usage = 0
        for session in user_sessions:
            data_usage = data_usage + session['data_usage']
            if data_usage >= voucher.data_limit:
                raise ValidationError('voucher data limit expired.')

                
                
                
View.py

class SessionHistoryCreate(generics.CreateAPIView):
    #model = models.SessionHistory
    serializer_class = serializers.SessionHistoryCreateSerializer

    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        serializer.validate_voucher_data_limit()
        self.perform_create(serializer)
        current_user = User.objects.get(username=serializer.validated_data.get('username'))
        response = {**current_user}
        return Response(response, status=status.HTTP_200_OK)