Django - Interview Questions and Answers

Django is a high-level Python web framework that enables rapid development of secure and maintainable websites. It follows the Model-View-Template (MVT) architecture.

• Built-in authentication
• ORM (Object-Relational Mapping)
• Middleware support
• Scalability and security
• Admin panel for easy management

• Model: Manages data and database interactions
• View: Handles business logic and user requests
• Template: Defines how data is presented to the user

Run:

django-admin startproject myproject

Run:

python manage.py startapp myapp

It is a command-line utility for managing a Django project, including database migrations, running the server, and creating superusers.

Django models define database tables using Python classes. Example:

from django.db import models
class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=50)
    published_date = models.DateField()

Django’s ORM allows interaction with the database using Python instead of SQL. Example:

books = Book.objects.all()  # Fetch all books

python manage.py makemigrations
python manage.py migrate
 

Views handle HTTP requests and responses. Example:

from django.http import HttpResponse
def home(request):
    return HttpResponse("Hello, Django!")

• Function-Based Views (FBV): Simple functions handling requests
• Class-Based Views (CBV): Use Python classes for better code reusability

Example of CBV:

from django.views import View
from django.http import HttpResponse

class HomeView(View):
    def get(self, request):
        return HttpResponse("Hello from CBV")

Templates define HTML structure with dynamic content using template tags.

Example:

<h1>Welcome {{ user.username }}</h1>

Middleware processes requests before reaching views and responses before sending them to clients.

In urls.py:

from django.urls import path
from . import views

urlpatterns = [
    path('', views.home, name='home'),
]

It contains all configuration settings like database setup, installed apps, and middleware.

The cycle involves the request passing through middleware, reaching the view, and returning a response.

Signals help decouple applications by sending notifications when an event occurs.

Example:

from django.db.models.signals import post_save
from django.dispatch import receiver
from .models import UserProfile

@receiver(post_save, sender=UserProfile)
def notify_user(sender, instance, **kwargs):
    print(f"User {instance.user} was updated")

Django provides django.contrib.auth for user authentication.

Run:

python manage.py createsuperuser

Django Forms simplify HTML form handling in Python.

Example:

from django import forms
class ContactForm(forms.Form):
    name = forms.CharField(max_length=50)
    email = forms.EmailField()

DRF helps create RESTful APIs in Django.

Example using DRF ViewSets:

from rest_framework import viewsets
from .models import Book
from .serializers import BookSerializer

class BookViewSet(viewsets.ModelViewSet):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

Django provides built-in caching to store frequently used data. Example:

from django.core.cache import cache
cache.set('key', 'value', timeout=60)

Django includes CSRF middleware to prevent cross-site request forgery attacks.

Celery is used for background task processing in Django.

Sessions store user-specific data across requests.

• Static Files: CSS, JavaScript, images
• Media Files: User-uploaded content

Django Admin can be customized using admin.py.
Example:

from django.contrib import admin
from .models import Book

class BookAdmin(admin.ModelAdmin):
    list_display = ('title', 'author')
    
admin.site.register(Book, BookAdmin)

Django provides logging for debugging.

Django provides protection against SQL injection, XSS, and CSRF.

• Django Signals are used to handle events like user creation or updates asynchronously.
• Middleware modifies requests or responses globally before they reach the view.

You can define multiple databases in settings.py:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'default_db',
        'USER': 'default_user',
        'PASSWORD': 'password',
        'HOST': 'localhost',
        'PORT': '5432',
    },
    'secondary': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'secondary_db',
        'USER': 'secondary_user',
        'PASSWORD': 'password',
        'HOST': 'localhost',
        'PORT': '3306',
    },
}

To query different databases:

from myapp.models import User
User.objects.using('secondary').all()

• ForeignKey: Many-to-one relationship
• OneToOneField: One-to-one relationship
• ManyToManyField: Many-to-many relationship

Example:

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

Use Django Channels to handle WebSockets:

pip install channels

In settings.py:

INSTALLED_APPS = [
    'channels',
    'myapp',
]
ASGI_APPLICATION = 'myproject.asgi.application'

Example consumer:

from channels.generic.websocket import AsyncWebsocketConsumer
import json

class ChatConsumer(AsyncWebsocketConsumer):
    async def connect(self):
        await self.accept()

    async def receive(self, text_data):
        data = json.loads(text_data)
        await self.send(text_data=json.dumps({'message': data['message']}))

Use Django’s built-in unittest framework:

from django.test import TestCase
from .models import Book

class BookTestCase(TestCase):
    def setUp(self):
        Book.objects.create(title="Test Book", author="John Doe")

    def test_book_title(self):
        book = Book.objects.get(title="Test Book")
        self.assertEqual(book.author, "John Doe")

Run tests:

python manage.py test

Use atomic to ensure a transaction is successful or rolled back:

from django.db import transaction

with transaction.atomic():
    user = User.objects.create(username="testuser")
    profile = Profile.objects.create(user=user)

1. Install Celery:

pip install celery

2. Configure Celery in settings.py:

CELERY_BROKER_URL = 'redis://localhost:6379/0'

3. Create a Celery task:

from celery import shared_task

@shared_task
def add(x, y):
    return x + y

4. Run Celery:

celery -A myproject worker --loglevel=info

1. Install Gunicorn:

pip install gunicorn

2. Run Django with Gunicorn:

gunicorn myproject.wsgi:application --bind 0.0.0.0:8000

3. Configure Nginx as a reverse proxy for Gunicorn.

• Use select_related() for foreign key relationships
• Use prefetch_related() for many-to-many relationships
• Avoid N+1 query problems
• Use indexes on frequently queried fields

Example:

books = Book.objects.select_related('author').all()

1. Install Redis:

pip install django-redis

2. Configure Redis in settings.py:

CACHES = {
    'default': {
        'BACKEND': 'django_redis.cache.RedisCache',
        'LOCATION': 'redis://127.0.0.1:6379/1',
    }
}

3. Use Redis for caching:

from django.core.cache import cache
cache.set('key', 'value', timeout=60)

Django supports multiple languages using:

from django.utils.translation import gettext_lazy as _

class Book(models.Model):
    title = models.CharField(max_length=100, verbose_name=_("Book Title"))

class Document(models.Model):
    file = models.FileField(upload_to='documents/')

In views.py:

from django.http import Http404

def my_view(request):
    if not some_condition:
        raise Http404("Page not found")

Custom 404 template:

{% block content %}
    <h1>Page Not Found</h1>
{% endblock %}

Use Django’s Group and Permission:

from django.contrib.auth.models import Group, Permission

group = Group.objects.create(name="Editors")
permission = Permission.objects.get(codename="change_article")
group.permissions.add(permission)

It restricts views to authenticated users:

from django.contrib.auth.decorators import login_required

@login_required
def dashboard(request):
    return render(request, "dashboard.html")

from django.http import JsonResponse

def my_view(request):
    data = {'message': 'Hello, Django!'}
    return JsonResponse(data)

Use reportlab:

pip install reportlab

Example PDF view:

from reportlab.pdfgen import canvas
from django.http import HttpResponse

def generate_pdf(request):
    response = HttpResponse(content_type='application/pdf')
    p = canvas.Canvas(response)
    p.drawString(100, 800, "Hello, PDF!")
    p.showPage()
    p.save()
    return response

Use Celery or cron jobs. Example using Celery:

@shared_task
def scheduled_task():
    print("Scheduled task executed")

• STATICFILES_DIRS: List of directories for static files during development
• STATIC_ROOT: The folder where collected static files are stored in production

In settings.py:

SECURE_SSL_REDIRECT = True
CSRF_COOKIE_SECURE = True
SESSION_COOKIE_SECURE = True

• get_object_or_404() returns an object or raises a 404 Not Found error if the object doesn’t exist.
• get() raises a DoesNotExist exception, which needs to be handled manually.

Example:

from django.shortcuts import get_object_or_404
from myapp.models import Book

book = get_object_or_404(Book, id=1)  # Returns a 404 error if not found

Django Signals allow decoupled applications to communicate when an event occurs.
Example: Execute a function after a user is created.

from django.db.models.signals import post_save
from django.dispatch import receiver
from django.contrib.auth.models import User
from myapp.models import Profile

@receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs):
    if created:
        Profile.objects.create(user=instance)

• ListView: Displays a list of objects.
• DetailView: Displays a single object.
• CreateView: Handles form submission to create an object.

Example:

from django.views.generic import ListView
from myapp.models import Book

class BookListView(ListView):
    model = Book
    template_name = 'book_list.html'

1. Create a templatetags directory inside your Django app.
2. Add a Python file (e.g., custom_filters.py).
3. Define the filter:

from django import template
register = template.Library()

@register.filter
def upper_case(value):
    return value.upper()

4. Use it in a template:

{{ "hello" | upper_case }}

Django supports various session backends:

• Database (django.contrib.sessions.backends.db)
• Cached (django.contrib.sessions.backends.cache)
• File-based (django.contrib.sessions.backends.file)

Enable sessions in settings.py:

SESSION_ENGINE = 'django.contrib.sessions.backends.cache'
SESSION_COOKIE_AGE = 3600  # Session expires in 1 hour

Set and get session data:

request.session["username"] = “DynamicUser”

usernamedata = request.session.get("username" “Guest”)
 

Django provides built-in authentication using django.contrib.auth.

• Login View:

from django.contrib.auth import authenticate, login

user = authenticate(request, username='admin', password='mypassword')
if user:
    login(request, user)

• Logout View:

from django.contrib.auth import logout

logout(request)

• Protect Views:

from django.contrib.auth.decorators import login_required

@login_required
def dashboard(request):
    return render(request, 'dashboard.html')

Use Django’s Paginator class for paginating query results.

from django.core.paginator import Paginator
from django.shortcuts import render
from myapp.models import Book

def book_list(request):
    book_objects = Book.objects.all()
    paginator = Paginator(book_objects, 10)  # 10 books per page
    page_number = request.GET.get('page')
    page_obj = paginator.get_page(page_number)
    return render(request, 'book_list.html', {'page_obj': page_obj})

1. SQL Injection: Use Django ORM instead of raw SQL.
2. CSRF Attacks: Enable csrf_token in forms.
3. XSS Attacks: Use Django’s built-in escaping in templates.
4. Clickjacking: Add X-Frame-Options header in settings.py:

X_FRAME_OPTIONS = 'DENY'

5. Use SECURE_SSL_REDIRECT = True to enforce HTTPS.

Django supports multiple caching backends like Redis, Memcached, and database caching.

1. Enable caching in settings.py:

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache',
        'LOCATION': '/var/tmp/django_cache',
    }
}

2. Cache a view using cache_page:

from django.views.decorators.cache import cache_page

@cache_page(60 * 15)  # Cache for 15 minutes
def my_view(request):
    ...

3. Set and get cache manually:

from django.core.cache import cache

cache.set('key', 'value', timeout=60)
data = cache.get('key')

Install Django REST Framework:

pip install djangorestframework

In settings.py:

INSTALLED_APPS = [
    'rest_framework',
    'myapp',
]

Define a Serializer:

from rest_framework import serializers
from myapp.models import Book

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

Define a ViewSet:

from rest_framework import viewsets
from myapp.models import Book
from myapp.serializers import BookSerializer

class BookViewSet(viewsets.ModelViewSet):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

Define URLs using a router:

from django.urls import path, include
from rest_framework.routers import DefaultRouter
from myapp.views import BookViewSet

router = DefaultRouter()
router.register(r'books', BookViewSet)

urlpatterns = [
    path('api/', include(router.urls)),
]