Creating the views

Before we create the views, we are going to create some helper classes and functions that will make the code in the view simpler and clean. Go ahead and create a file called view_helper.py in the main app directory, and as usual, let's start by including the import statements:

from rest_framework import generics, status
from rest_framework.response import Response

from django.http import HttpResponse

from .exceptions import InvalidArgumentError
from .exceptions import OrderAlreadyCancelledError
from .exceptions import OrderAlreadyCompletedError

from .serializers import OrderSerializer

Here, we import some things from the Django REST Framework, the main one being the generic, which contains definitions for the generic view classes that we are going to use to create our own custom views. The status contains all the HTTP status codes, which are very useful when sending the response back to the client. Then, we import the Response class, which will allow us to send content...