Function Based and Class Based API Views

When developing APIs in Django REST Framework (DRF), developers have multiple approaches to structuring views. Two of the most common approaches are Function-Based Views (FBVs) and Class-Based Views (CBVs).

Although DRF provides higher-level abstractions like ViewSets and Generic Views, understanding function-based and class-based views remains essential because they form the foundation of how DRF processes HTTP requests and responses.

This comprehensive guide explores both approaches in depth — how they work, when to use them, their differences, and how they fit into a modern Django project.

Table of Contents

1. Introduction to Django REST Framework Views
2. The Concept of Views in Django
3. Function-Based API Views (FBVs)
4. Class-Based API Views (CBVs)
5. Comparing Function-Based and Class-Based API Views
6. Example: Creating an API with Function-Based Views
7. Example: Creating an API with Class-Based Views
8. Handling Different HTTP Methods
9. Adding POST, PUT, and DELETE Methods
10. Using Request Data and Query Parameters
11. Exception Handling in API Views
12. Permissions and Authentication in Views
13. Pagination and Filtering with Class-Based Views
14. Extending APIView for Custom Logic
15. Using Mixins for Reusability
16. Switching from Function-Based to Class-Based Views
17. Best Practices for Structuring DRF Views
18. Common Mistakes and Debugging Tips
19. Combining ViewSets, FBVs, and CBVs in One Project
20. Final Thoughts

1. Introduction to Django REST Framework Views

Django REST Framework is built on Django’s powerful class-based view system. In DRF, views are responsible for handling incoming requests, performing operations on data, and returning serialized responses in formats such as JSON or XML.

At the most fundamental level, a DRF view:

• Receives an HTTP request.
• Executes business logic (e.g., queries a database).
• Serializes data using DRF’s serializers.
• Returns a Response object.

DRF provides three main levels of abstraction for building views:

1. Function-Based Views (@api_view)
2. Class-Based Views (APIView)
3. ViewSets (automated CRUD interface)

While ViewSets are excellent for standard APIs, function-based and class-based views give you fine-grained control over how your API behaves.

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2. The Concept of Views in Django

In Django, a view is a Python function or class that takes a request and returns a response.

In standard Django, you might write something like:

from django.http import HttpResponse

def hello_world(request):
return HttpResponse("Hello, world!")

In Django REST Framework, instead of returning plain HTML, we return serialized data — typically JSON — using DRF’s Response class.

Thus, DRF views are simply Django views enhanced with RESTful capabilities.

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3. Function-Based API Views (FBVs)

A Function-Based View (FBV) is the simplest form of API view in DRF. You define it as a regular Python function and use the @api_view decorator to specify which HTTP methods it supports.

Example:

from rest_framework.decorators import api_view
from rest_framework.response import Response
from .models import Book
from .serializers import BookSerializer

@api_view(['GET'])
def book_list(request):
books = Book.objects.all()
serializer = BookSerializer(books, many=True)
return Response(serializer.data)

Key Features

1. Simplicity: Easy to read and understand for beginners.
2. Explicit Control: You directly define how each HTTP method is handled.
3. Quick Setup: Great for small projects or prototyping.

How It Works

• The @api_view decorator converts a standard Django function into a DRF-compatible API view.
• It ensures incoming data is parsed correctly and provides the request.data object.
• The function can return DRF’s Response objects, which automatically handle content negotiation (e.g., JSON vs XML).

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4. Class-Based API Views (CBVs)

While function-based views are simple, they can become difficult to manage as your project grows.

That’s why Django REST Framework provides Class-Based Views (CBVs) through the APIView class.

Example:

from rest_framework.views import APIView
from rest_framework.response import Response
from .models import Book
from .serializers import BookSerializer

class BookList(APIView):
def get(self, request):
    books = Book.objects.all()
    serializer = BookSerializer(books, many=True)
    return Response(serializer.data)

How It Works

• Each HTTP method (GET, POST, PUT, DELETE) is represented as a class method.
• The class-based view handles request parsing and response rendering automatically.
• You can use inheritance, mixins, and class attributes to make the code reusable and maintainable.

Advantages

1. Reusability: Share behavior through inheritance and mixins.
2. Organization: Better structure for large APIs.
3. Extensibility: Easily integrate middleware, permissions, and custom logic.

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5. Comparing Function-Based and Class-Based API Views

Feature	Function-Based Views	Class-Based Views
Definition Style	Function	Class
Simplicity	Simple and straightforward	Slightly complex but scalable
Reusability	Limited	High (supports inheritance)
Maintainability	Suitable for small APIs	Best for large projects
Control	Fine-grained but repetitive	Structured and extendable
Preferred Use Case	Quick prototypes, small APIs	Enterprise-grade or complex APIs

In short, FBVs are great for simplicity, while CBVs are ideal for scalability and maintainability.

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6. Example: Creating an API with Function-Based Views

Let’s build a simple REST API using a function-based approach.

models.py

from django.db import models

class Book(models.Model):
title = models.CharField(max_length=100)
author = models.CharField(max_length=100)
published_date = models.DateField()
def __str__(self):
    return self.title

serializers.py

from rest_framework import serializers
from .models import Book

class BookSerializer(serializers.ModelSerializer):
class Meta:
    model = Book
    fields = '__all__'

views.py

from rest_framework.decorators import api_view
from rest_framework.response import Response
from rest_framework import status
from .models import Book
from .serializers import BookSerializer

@api_view(['GET', 'POST'])
def book_list(request):
if request.method == 'GET':
    books = Book.objects.all()
    serializer = BookSerializer(books, many=True)
    return Response(serializer.data)
elif request.method == 'POST':
    serializer = BookSerializer(data=request.data)
    if serializer.is_valid():
        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)
    return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

urls.py

from django.urls import path
from . import views

urlpatterns = [
path('books/', views.book_list, name='book-list'),
]

Now, visiting /books/ with a GET request lists all books, and a POST request adds a new one.

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7. Example: Creating an API with Class-Based Views

Let’s create the same functionality using class-based views.

views.py

from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status
from .models import Book
from .serializers import BookSerializer

class BookList(APIView):
def get(self, request):
    books = Book.objects.all()
    serializer = BookSerializer(books, many=True)
    return Response(serializer.data)
def post(self, request):
    serializer = BookSerializer(data=request.data)
    if serializer.is_valid():
        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)
    return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

urls.py

from django.urls import path
from .views import BookList

urlpatterns = [
path('books/', BookList.as_view(), name='book-list'),
]

Note that for CBVs, you use .as_view() to convert the class into a callable view that Django can process.

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8. Handling Different HTTP Methods

Both FBVs and CBVs can handle multiple HTTP methods.

For example, an FBV supporting GET, PUT, and DELETE might look like this:

@api_view(['GET', 'PUT', 'DELETE'])
def book_detail(request, pk):
try:
    book = Book.objects.get(pk=pk)
except Book.DoesNotExist:
    return Response({'error': 'Book not found'}, status=404)
if request.method == 'GET':
    serializer = BookSerializer(book)
    return Response(serializer.data)
elif request.method == 'PUT':
    serializer = BookSerializer(book, data=request.data)
    if serializer.is_valid():
        serializer.save()
        return Response(serializer.data)
    return Response(serializer.errors, status=400)
elif request.method == 'DELETE':
    book.delete()
    return Response(status=204)

The same behavior using a CBV:

class BookDetail(APIView):
def get_object(self, pk):
    try:
        return Book.objects.get(pk=pk)
    except Book.DoesNotExist:
        raise Http404
def get(self, request, pk):
    book = self.get_object(pk)
    serializer = BookSerializer(book)
    return Response(serializer.data)
def put(self, request, pk):
    book = self.get_object(pk)
    serializer = BookSerializer(book, data=request.data)
    if serializer.is_valid():
        serializer.save()
        return Response(serializer.data)
    return Response(serializer.errors, status=400)
def delete(self, request, pk):
    book = self.get_object(pk)
    book.delete()
    return Response(status=204)

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9. Adding POST, PUT, and DELETE Methods

CBVs make it clean to define behavior for different methods — simply create methods named after HTTP verbs.

Supported methods include get(), post(), put(), patch(), delete(), and head().

FBVs achieve the same via conditional branching inside the function, but CBVs are cleaner and more structured.

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10. Using Request Data and Query Parameters

DRF makes it easy to access incoming data and query parameters.

• Request Data: request.data
• Query Params: request.query_params

Example:

class FilteredBooks(APIView):
def get(self, request):
    author = request.query_params.get('author')
    if author:
        books = Book.objects.filter(author=author)
    else:
        books = Book.objects.all()
    serializer = BookSerializer(books, many=True)
    return Response(serializer.data)

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11. Exception Handling in API Views

DRF provides global and local exception handling.

For example:

from rest_framework.exceptions import NotFound

class BookDetail(APIView):
def get(self, request, pk):
    try:
        book = Book.objects.get(pk=pk)
    except Book.DoesNotExist:
        raise NotFound('Book not found')
    serializer = BookSerializer(book)
    return Response(serializer.data)

You can also use Django’s Http404 exception or custom responses.

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12. Permissions and Authentication in Views

To restrict access, use DRF’s permission classes.

Example:

from rest_framework.permissions import IsAuthenticated

class BookList(APIView):
permission_classes = [IsAuthenticated]
def get(self, request):
    books = Book.objects.all()
    serializer = BookSerializer(books, many=True)
    return Response(serializer.data)

Now, only authenticated users can access this view.

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13. Pagination and Filtering with Class-Based Views

Pagination is configured globally in settings:

REST_FRAMEWORK = {
'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.PageNumberPagination',
'PAGE_SIZE': 10
}

Then any view that returns a queryset automatically gets paginated through DRF’s response rendering system.

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14. Extending APIView for Custom Logic

You can extend APIView to create your own reusable base view:

class CustomAPIView(APIView):
def handle_exception(self, exc):
    response = super().handle_exception(exc)
    response.data['status_code'] = response.status_code
    return response

All views that inherit from this will include an extra field in their error responses.

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15. Using Mixins for Reusability

Mixins allow you to combine common behaviors.

For example:

from rest_framework import mixins, generics

class BookListCreateView(mixins.ListModelMixin,
                     mixins.CreateModelMixin,
                     generics.GenericAPIView):
queryset = Book.objects.all()
serializer_class = BookSerializer
def get(self, request, *args, **kwargs):
    return self.list(request, *args, **kwargs)
def post(self, request, *args, **kwargs):
    return self.create(request, *args, **kwargs)

Mixins provide reusable components that define CRUD operations.

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16. Switching from Function-Based to Class-Based Views

It’s common to start with FBVs and later move to CBVs as the project grows.

Migration is simple:

• Each function becomes a class method (get, post, etc.).
• Shared logic moves into helper methods like get_object().
• URL routes switch from direct functions to .as_view().

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17. Best Practices for Structuring DRF Views

1. Use FBVs for Simple APIs: They’re great for prototypes and small endpoints.
2. Use CBVs for Scalability: Especially when you expect to add more functionality later.
3. Keep Views Thin: Move business logic to serializers or models.
4. Use Mixins and Generics: Reduce code duplication.
5. Always Handle Exceptions Gracefully: Provide user-friendly error responses.

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18. Common Mistakes and Debugging Tips

1. Missing .as_view() in CBVs: Always call .as_view() in urls.py.
2. Incorrect Method Names: Use lowercase HTTP method names (get, not GET).
3. Improper Imports: Import Response from rest_framework.response, not django.http.
4. Uncaught Exceptions: Use try-except blocks or DRF exceptions.
5. Forgot Permissions: Always define proper permission classes for secure endpoints.

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19. Combining ViewSets, FBVs, and CBVs in One Project

You can freely mix all three types within one Django project.

For example:

• Use ViewSets for standard CRUD APIs.
• Use CBVs for customized workflows.
• Use FBVs for simple utilities or webhook handlers.

This flexibility is one of Django REST Framework’s greatest strengths.