Current Method

question.py

# This my current application code (Booking system have not been implemented)
# The Current Flow of this version:
# 1. The user selects the food/drinks.
# 2. The user enters his table number.
# 3. The user makes payment
# 4. The kiosk process the order. (POST to ORDER then POST to ORDERDETAIL). 
#    If Failed (The QTY is not sufficient), the KIOSK return the user's money.
#    If success then continue to the next step.
# 5. Order is done. The kiosk print the receipt.

# You can see that there is an non-normal process, the KIOSK return the user's money. 
# So I would like to change that, since it is not real and does not make sense. 
# Imagine your card has been debt then the machine return back the debt when the qty of your order is not sufficient. -_-

#1 Make POST request to ORDER (CLIENT do this)
data = 'cardID=123456&amount=1200000'

#2 Response From Server 
{'id': 40, 'cardID': 123456, 'amount': 500000, 'time': '2019-05-17T11:11:38.384667+07:00'} # I use the ID as the orderID

#3 Make POST request to ORDERDETAIL (CLIENT do this)
data = '[{"menuID": 3, "price": 100000, "qty": 4, "sellerID": 1, "tableNumber": 56, "orderID": "40"}, 
        {"menuID": 2, "price": 50000, "qty": 2, "sellerID": 2, "tableNumber": 56, "orderID": "40"}]'

#4 Checking the QTY in the SERVER (Kindly check the full code of the server at my github)
    # Filename: api_views.py
    # Enable Post of List
    # https://stackoverflow.com/questions/37329771/django-rest-bulk-post-post-array-of-json-objects
    # Accessed on March 9, 2019
    def create(self, request, pk=None, company_pk=None, project_pk=None):
        is_many = True if isinstance(request.data, list) else False

        serializer = self.get_serializer(data=request.data, many=is_many)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)
        
    # Filename: models.py    
    def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
        if self.done:
            self.finishTime = datetime.datetime.now()
        else:
            menuID = self.menuID.id
            menuObject = Menu.objects.get(id=menuID)
            tempQty = menuObject.qty - self.qty
            if tempQty>=0:
                menuObject.qty = tempQty
                menuObject.save()
            else:
                # return serializers.ValidationError()
                raise serializers.ValidationError(menuObject.name + ": STOCK IS NOT SUFFICIENT")
        super().save(force_insert, force_update, using, update_fields)



#5 Response From Serverif success
[{'id': 41, 'orderID': 40, 'sellerID': 1, 'menuID': 3, 'menuName': 'Nasi Goreng', 
    'image': 'http://127.0.0.1:8000/media/media/Nasi_Goreng_ACL6BZG.jpg', 'price': 100000, 'qty': 4, 
    'tableNumber': 56, 'done': False, 'orderTime': '2019-05-17T11:11:38.384667+07:00', 'finishTime': None}, 
  {'id': 42, 'orderID': 40, 'sellerID': 2, 'menuID': 2, 'menuName': 'Soju', 
  'image': 'http://127.0.0.1:8000/media/media/Soju_gTvqW4D.jpg', 'price': 50000, 'qty': 2, 
  'tableNumber': 56, 'done': False, 'orderTime': '2019-05-17T11:11:38.384667+07:00', 'finishTime': None}]