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Django Rest Framework Beginner Cheatsheet

Estee Tey
A gamer, designer and builder. I enjoy thinking about how and why we code.
・Updated on ・4 min read

Hello there! This cheatsheet is written by a user who just learnt Django & DRF recently, for other users who are also relatively new to Django Rest Framework (DRF) like @jasonbraganza . Do check out his series on his learning journey for Django😄

Join in the fun with #CNC2021 if you are not part of it already!


Table of Contents


Python 🐍

Keyword and positional arguments

  • Keyword argument: kwarg=value
  • Example: def function(name='hehe') , name is the kwarg.
  • In a function call, keyword arguments must follow positional arguments.

    def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):
          -----------    ----------     ----------
            |             |                  |
            |        Positional or keyword   |
            |                                - Keyword only
             -- Positional only
    

Retrieved from Python 3.9.4 documentation

*args, **kwargs

>>> def functionA(*a, **kw):
       print(a)
       print(kw)

>>> functionA(1, 2, 3, 4, 5, 6, a=2, b=3, c=5)
(1, 2, 3, 4, 5, 6)
{'a': 2, 'c': 5, 'b': 3}

>>> lis=[1, 2, 3, 4]
>>> dic={'a': 10, 'b':20}
>>> functionA(*lis, **dic)
(1, 2, 3, 4)
{'a': 10, 'b': 20}
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Retrieved from Stackoverflow Post on What do * and ** before a variable name mean in a function signature?


Django

Basic commands

Make an app

djangoadmin startapp $APP_NAME
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Register the app in settings.py

INSTALLED_APPS = [$APP_NAME, ...]
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Make super user (admin)

python3 manage.py makesuperuser
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Make migrations and perform migrations

Migration file created will be named like $APP_NAME/migrations/001.py

python3 manage.py makemigration $APP_NAME
python3 manage.py migrate $APP_NAME
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Using Django Shell to get Model Object Instance

Getters

>>> Question.objects.all()
<QuerySet [<Question: Question object (1)>]> # if model does not have __str__

>>> q.choice_set.all()
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]> # if related model has __str__

>>> Question.objects.get(pk=1)
<Question: What's up?> 
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Filters

>>> Choice.objects.filter(question__pub_date__year=current_year)
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
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Signals

Docs

from django.db.models.signals import pre_save
from django.dispatch import receiver
from myapp.models import MyModel

@receiver(pre_save, sender=MyModel)
def my_handler(sender, **kwargs):
    ...
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DRF

Serialization

Serialization is the following data flow sequence:

Serialization Data Flow

In Code,

from rest_framework import serializers

class Comment:
    def __init__(self, email, content, created=None):
        self.email = email
        self.content = content
        self.created = created or datetime.now()

class CommentSerializer(serializers.Serializer):
    email = serializers.EmailField()
    content = serializers.CharField(max_length=200)
    created = serializers.DateTimeField()

# Create the Model Instance
comment = Comment(email='leila@example.com', content='foo bar')

# Serialize the data and store it in native python data type
serializer = CommentSerializer(comment) 

# Render the native python data type into JSON
json = JSONRenderer().render(serializer.data)
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Deserialization

The reverse of serialization

import io
from rest_framework.parsers import JSONParser

# Translate the JSON into a parsable stream
stream = io.BytesIO(json) 

# Parse the stream 
data = JSONParser().parse(stream)
serializer = CommentSerializer(data=data)

# Check if serialized data is valid, if yes then do something with it
if (serializer.is_valid()):
 validated_data = serializer.validated_data
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API Views

Docs

API Views are split into Functional decorators @api_view & Class-based APIView

Functional decorator with @api_view

from rest_framework.views import APIView
from rest_framework.response import Response

@api_view(['GET', 'POST']) # add other methods as necessary
def hello_world(request):
  if request.method == 'GET':
   return Response({"message": "Hello, world!"})
    else if request.method == 'POST':
        return Response({"message": "Got some data!", "data": request.data})
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Class-based view with APIView

class HelloWorld(APIView):
    def get(self, request):
        return Response({"message": "Hello, world!"})
  def post(self, request):
    return Response({"message": "Got some data!", "data": request.data})
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Validation

Docs

Field level validation and object level validation

Field level validation relies on the declaration of specific fields within a model class, while object level validation relies on the use of serializers and then checking whether serializer.is_valid().

Permissions

Docs

Global: DEFAULT_PERMISSIONS_LEVEL

REST_FRAMEWORK = {
    'DEFAULT_PERMISSION_CLASSES': [
        'rest_framework.permissions.IsAuthenticated',
    ]
}
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Specific views only

  • for @api_view, add decorator @permission_classes([])
  • for class-based view, add variable permission_classes = [ ]

Pagination

Docs

Global: DEFAULT_PAGINATION_CLASS

 REST_FRAMEWORK = {
    'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.PageNumberPagination',
    'PAGE_SIZE': 3
}
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Specific views only: make a class that extends PageNumberPagination

Also, for APIs that you intend to add pagination, you should make sure that the items are ordered, otherwise it may yield inconsistent results.

class StandardResultsSetPagination(PageNumberPagination):
    page_size = 100
    page_size_query_param = 'page_size'
    max_page_size = 1000

class BillingRecordsView(generics.ListAPIView):
    queryset = Billing.objects.all().order_by("-id")
    serializer_class = BillingRecordsSerializer
    pagination_class = StandardResultsSetPagination
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After adding pagination, the response will look like the below

{
    "count": 1023
    "next": "https://api.example.org/accounts/?page=5",
    "previous": "https://api.example.org/accounts/?page=3",
    "results": [
       …
    ]
}
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Authentication

Docs

Global: DEFAULT_AUTHENTICATION_CLASSES

REST_FRAMEWORK = {
    'DEFAULT_AUTHENTICATION_CLASSES': [
        'rest_framework.authentication.BasicAuthentication',
        'rest_framework.authentication.SessionAuthentication',
    ]
}
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Specific Views only

  • @api_view: add decorator @authentication_classes([])
  • Class-based view: add variable authentication_classes = []

If using token authentication, DRF provides a default view

from rest_framework.authtoken import views
urlpatterns += [
    path('api-token-auth/', views.obtain_auth_token)
]
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which returns the response below if given a valid username and password

{ 'token' : '9944b09199c62bcf9418ad846dd0e4bbdfc6ee4b' }
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