Django

Django

Comprehensive guide to Django covering security, ORM, PostgreSQL, GeoDjango, Django 6.0 essentials, admin extensions, and ecosystem tools.

Overview

Django provides a batteries-included web framework with robust features out of the box:

• Security - CSRF protection, authentication, sessions, password hashing, security middleware
• ORM - Powerful database abstraction with query optimization
• PostgreSQL - Full-text search, array fields, JSONB, range fields
• GeoDjango - Geographic database operations with GPS extraction
• Django 6.0 - Middleware changes, built-in tasks framework, CSP, GeneratedField
• Admin Extensions - Operational dashboards and monitoring tools Django provides robust security features out of the box:
• CSRF Protection - Prevents cross-site request forgery
• Authentication - User login/logout, password management
• Sessions - Secure session management
• Security Middleware - Various security headers
• Password Hashing - Secure password storage

CSRF Protection

How CSRF Works

CSRF (Cross-Site Request Forgery) prevents malicious sites from submitting forms on behalf of authenticated users.

User logs in → Django sets session cookie → User visits malicious site
                                                      ↓
                                    Malicious site submits form to your site
                                                      ↓
                                    CSRF token missing → Request rejected

CsrfViewMiddleware

Django's CsrfViewMiddleware provides CSRF protection:

# settings.py
MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',  # Must be here
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
]

Important: CsrfViewMiddleware must come AFTER SessionMiddleware.

Using CSRF Token in Forms

<!-- Required in every POST form -->
<form method="post">
    {% csrf_token %}
    <input type="text" name="username">
    <input type="password" name="password">
    <button type="submit">Login</button>
</form>

<!-- AJAX requests -->
<script>
function submitForm() {
    fetch('/submit/', {
        method: 'POST',
        body: new FormData(document.getElementById('myForm')),
        headers: {
            'X-CSRFToken': '{{ csrf_token }}'
        }
    });
}
</script>

// JavaScript helper
function getCookie(name) {
    let cookieValue = null;
    if (document.cookie && document.cookie !== '') {
        const cookies = document.cookie.split(';');
        for (let i = 0; i < cookies.length; i++) {
            const cookie = cookies[i].trim();
            if (cookie.substring(0, name.length + 1) === (name + '=')) {
                cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
                break;
            }
        }
    }
    return cookieValue;
}

// Usage
fetch('/api/', {
    method: 'POST',
    body: JSON.stringify(data),
    headers: {
        'Content-Type': 'application/json',
        'X-CSRFToken': getCookie('csrftoken')
    }
});

csrf_protect Decorator

Apply CSRF protection to specific views:

from django.views.decorators.csrf import csrf_protect
from django.middleware.csrf import csrf_exempt

@csrf_protect
def protected_view(request):
    """This view requires CSRF protection."""
    pass

@csrf_exempt
def exempt_view(request):
    """This view is exempt from CSRF (use carefully!)."""
    pass

AJAX with CSRF

# Using Django's CSRF helper in JavaScript
import Cookies from 'js-cookie';

const csrftoken = Cookies.get('csrftoken');

// Fetch API
fetch('/api/', {
    method: 'POST',
    headers: {
        'X-CSRFToken': csrftoken
    },
    body: formData
});

// Axios
axios.defaults.headers.common['X-CSRFToken'] = csrftoken;

// jQuery
$.ajaxSetup({
    headers: {
        'X-CSRFToken': '{{ csrf_token }}'
    }
});

CSRF Exemption (Use Carefully)

# Only exempt when absolutely necessary
from django.views.decorators.csrf import csrf_exempt
from django.utils.decorators import method_decorator
from django.views import View

@method_decorator(csrf_exempt, name='dispatch')
class WebhookView(View):
    """Webhooks from trusted services."""
    def post(self, request):
        # Process webhook
        return JsonResponse({'status': 'ok'})

Testing CSRF

from django.test import Client, override_settings

@override_settings(CSRFmiddleware=None)  # Disable for testing
def test_view_without_csrf(client):
    """Test without CSRF (not recommended)."""
    response = client.post('/url/', {'data': 'value'})
    assert response.status_code == 200

# Better: Use CSRF client
def test_view_with_csrf(client):
    """Test with proper CSRF token."""
    # Get the form first to obtain CSRF token
    response = client.get('/form-url/')
    csrf_token = client.cookies.get('csrftoken').value
    
    # POST with token
    response = client.post('/form-url/', {
        'field': 'value',
        'csrfmiddlewaretoken': csrf_token
    })
    assert response.status_code == 200

Authentication

Built-in Authentication Views

# urls.py
from django.contrib.auth import views as auth_views
from django.urls import path

urlpatterns = [
    path('login/', auth_views.LoginView.as_view(), name='login'),
    path('logout/', auth_views.LogoutView.as_view(), name='logout'),
    path('password_change/', auth_views.PasswordChangeView.as_view(), name='password_change'),
    path('password_change/done/', auth_views.PasswordChangeDoneView.as_view(), name='password_change_done'),
    path('password_reset/', auth_views.PasswordResetView.as_view(), name='password_reset'),
    path('password_reset/done/', auth_views.PasswordResetDoneView.as_view(), name='password_done'),
    path('reset/<uidb64>/<token>/', auth_views.PasswordResetConfirmView.as_view(), name='password_reset_confirm'),
    path('reset/done/', auth_views.PasswordResetCompleteView.as_view(), name='password_reset_complete'),
]

LoginView Configuration

# views.py
from django.contrib.auth.views import LoginView
from django.contrib.auth.forms import AuthenticationForm

class CustomLoginView(LoginView):
    template_name = 'registration/login.html'
    authentication_form = AuthenticationForm
    redirect_authenticated_user = True
    
    def get_success_url(self):
        return self.request.GET.get('next', '/dashboard/')

# settings.py
LOGIN_URL = '/accounts/login/'
LOGIN_REDIRECT_URL = '/dashboard/'
LOGOUT_REDIRECT_URL = '/'

Manual Authentication

from django.contrib.auth import authenticate, login, logout

def login_view(request):
    username = request.POST.get('username')
    password = request.POST.get('password')
    
    # Authenticate user
    user = authenticate(request, username=username, password=password)
    
    if user is not None:
        if user.is_active:
            login(request, user)
            # Redirect to success page
            return redirect('dashboard')
        else:
            return render(request, 'login.html', {
                'error': 'Account disabled'
            })
    else:
        return render(request, 'login.html', {
            'error': 'Invalid credentials'
        })

def logout_view(request):
    logout(request)
    return redirect('home')

Authentication Form

from django.contrib.auth.forms import AuthenticationForm, UserCreationForm

# Login form
form = AuthenticationForm(request, data=request.POST)

if form.is_valid():
    user = form.get_user()
    login(request, user)

# Registration form
form = UserCreationForm(request.POST)
if form.is_valid():
    user = form.save()
    login(request, user)  # Auto-login after registration

LoginRequiredMixin

from django.contrib.auth.mixins import LoginRequiredMixin

class DashboardView(LoginRequiredMixin, View):
    login_url = '/accounts/login/'
    redirect_field_name = 'next'
    
    def get(self, request):
        return render(request, 'dashboard.html')

# Function-based view
from django.contrib.auth.decorators import login_required

@login_required(login_url='/accounts/login/')
def dashboard(request):
    return render(request, 'dashboard.html')

Custom User Model Authentication

# For custom User models with email instead of username
from django.contrib.auth.backends import BaseBackend
from django.contrib.auth import get_user_model

User = get_user_model()

class EmailBackend(BaseBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        try:
            user = User.objects.get(email=username)
        except User.DoesNotExist:
            return None
        
        if user.check_password(password):
            return user
        return None
    
    def get_user(self, user_id):
        try:
            return User.objects.get(pk=user_id)
        except User.DoesNotExist:
            return None

# settings.py
AUTHENTICATION_BACKENDS = [
    'path.to.EmailBackend',
    'django.contrib.auth.backends.ModelBackend',
]

Custom Permission Backends

Why Custom Backends

Django's built-in ModelBackend only handles model-level permissions (add, change, delete, view). Custom backends add:

• Per-object permissions (row-level authorization)
• External auth systems (LDAP, OAuth providers)
• Permission composition (multiple backends chained)

Custom Backend Implementation

# myapp/backends.py
from django.contrib.auth.backends import BaseBackend
from django.contrib.auth.models import User

class ObjectPermissionBackend(BaseBackend):
    """Backend for per-object permissions."""
    
    def has_perm(self, user_obj, perm, obj=None):
        if obj is None:
            # Fall back to model-level check
            return None
        
        app_label, codename = perm.split('.')
        
        # Check object-level permission
        return self._check_object_perm(user_obj, obj, codename)
    
    def _check_object_perm(self, user_obj, obj, action):
        """Check if user can perform action on specific object."""
        if action == 'view':
            return self._can_view(user_obj, obj)
        if action == 'change':
            return self._can_change(user_obj, obj)
        if action == 'delete':
            return self._can_delete(user_obj, obj)
        return False
    
    def _can_view(self, user, obj):
        if hasattr(obj, 'owner'):
            return obj.owner_id == user.id or user.is_staff
        return True
    
    def _can_change(self, user, obj):
        if hasattr(obj, 'owner'):
            return obj.owner_id == user.id
        return user.is_staff

Configuration

Chaining multiple backends:

# settings.py
AUTHENTICATION_BACKENDS = [
    'django.contrib.auth.backends.ModelBackend',  # Default model-level
    'myapp.backends.ObjectPermissionBackend',      # Custom object-level
]

Django tries each backend in order; first True or False wins. None means "I don't know, ask the next backend".

Per-Object Permissions

The row-level authorization pattern:

from django.contrib.auth.decorators import permission_required
from django.shortcuts import get_object_or_404

@permission_required('myapp.change_document')
def edit_document(request, pk):
    document = get_object_or_404(Document, pk=pk)
    
    # Check object-level permission
    if not request.user.has_perm('myapp.change_document', document):
        from django.core.exceptions import PermissionDenied
        raise PermissionDenied
    
    # Proceed with edit...

Permission Flow Design

The request → check → grant/deny pattern:

# myapp/permissions.py
class PermissionFlow:
    """Centralized permission checking with audit logging."""
    
    def __init__(self, user):
        self.user = user
    
    def can_access(self, resource, action, obj=None):
        """Check permission and log the decision."""
        allowed = self.user.has_perm(
            f'{resource}.{action}', 
            obj=obj
        )
        
        if not allowed:
            # Log denied access for audit trail
            import logging
            logger = logging.getLogger('permissions')
            logger.warning(
                f"Permission denied: user={self.user.id}, "
                f"resource={resource}, action={action}, obj={obj}"
            )
        
        return allowed

Class-Based View Mixin

Reusable permission checks in CBVs:

from django.core.exceptions import PermissionDenied

class ObjectPermissionMixin:
    """Mixin for per-object permission checks in CBVs."""
    permission_required = None  # e.g., 'myapp.change_document'
    
    def get_object(self, queryset=None):
        obj = super().get_object(queryset)
        if self.permission_required:
            if not self.request.user.has_perm(
                self.permission_required, obj
            ):
                raise PermissionDenied
        return obj

Testing Permissions

How to test custom backends:

from django.test import TestCase
from django.contrib.auth.models import User, Permission
from myapp.models import Document

class ObjectPermissionTest(TestCase):
    def setUp(self):
        self.owner = User.objects.create_user('owner', 'o@e.com', 'pass')
        self.other = User.objects.create_user('other', 'x@e.com', 'pass')
        self.doc = Document.objects.create(title='Test', owner=self.owner)
    
    def test_owner_can_change(self):
        self.assertTrue(
            self.owner.has_perm('myapp.change_document', self.doc)
        )
    
    def test_other_cannot_change(self):
        self.assertFalse(
            self.other.has_perm('myapp.change_document', self.doc)
        )

Common Pitfalls

Sessions

Session Configuration

# settings.py
SESSION_ENGINE = 'django.contrib.sessions.backends.db'  # Default
# Or:
SESSION_ENGINE = 'django.contrib.sessions.backends.cache'  # Faster
SESSION_ENGINE = 'django.contrib.sessions.backends.signed_cookies'  # No server storage

SESSION_COOKIE_NAME = 'sessionid'
SESSION_COOKIE_AGE = 60 * 60 * 24 * 7  # 1 week in seconds
SESSION_COOKIE_SECURE = True  # HTTPS only
SESSION_COOKIE_HTTPONLY = True  # No JavaScript access
SESSION_COOKIE_SAMESITE = 'Lax'  # CSRF protection

Using Sessions

# Set session data
request.session['user_id'] = user.id
request.session['preferences'] = {'theme': 'dark', 'lang': 'en'}

# Get session data
user_id = request.session.get('user_id')
preferences = request.session.get('preferences', {})

# Delete session data
del request.session['user_id']
request.session.flush()  # Clear all session data

# Check if key exists
if 'user_id' in request.session:
    pass

Session Middleware

# settings.py - Ensure these are in MIDDLEWARE
'django.contrib.sessions.middleware.SessionMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',

Password Management

Password Validation

# settings.py
AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
        'OPTIONS': {'min_length': 8},
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]

Custom Password Validation

# validators.py
from django.core.exceptions import ValidationError
import re

class CustomPasswordValidator:
    def __init__(self, min_length=8):
        self.min_length = min_length
    
    def validate(self, password, user=None):
        if len(password) < self.min_length:
            raise ValidationError(f'Password must be at least {self.min_length} characters.')
        
        if not re.search(r'[A-Z]', password):
            raise ValidationError('Password must contain at least one uppercase letter.')
        
        if not re.search(r'[!@#$%^&*]', password):
            raise ValidationError('Password must contain at least one special character.')
    
    def help_text(self):
        return f'Password must be at least {self.min_length} characters with uppercase and special characters.'

# settings.py
AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'myapp.validators.CustomPasswordValidator',
    },
]

Changing Password

from django.contrib.auth import update_session_auth_hash

def change_password(request):
    if request.method == 'POST':
        form = PasswordChangeForm(user=request.user, data=request.POST)
        if form.is_valid():
            user = form.save()
            # Keep user logged in
            update_session_auth_hash(request, user)
            return redirect('password_change_done')
    else:
        form = PasswordChangeForm(user=request.user)
    
    return render(request, 'password_change.html', {'form': form})

Security Middleware

# settings.py
MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    # ... other middleware
]

# Security settings
SECURE_BROWSER_XSS_FILTER = True
SECURE_CONTENT_TYPE_NOSNIFF = True
X_FRAME_OPTIONS = 'DENY'
SECURE_REFERRER_POLICY = 'strict-origin-when-cross-origin'

# HTTPS settings
SECURE_SSL_REDIRECT = True  # Redirect HTTP to HTTPS
SESSION_COOKIE_SECURE = True
CSRF_COOKIE_SECURE = True

# HSTS (HTTP Strict Transport Security)
SECURE_HSTS_SECONDS = 31536000  # 1 year
SECURE_HSTS_INCLUDE_SUBDOMAINS = True
SECURE_HSTS_PRELOAD = True

SecurityMiddleware Options

# settings.py
SECURE_CONTENT_TYPE_NOSNIFF = True  # Prevent MIME sniffing
X_FRAME_OPTIONS = 'DENY'  # Prevent clickjacking
SECURE_BROWSER_XSS_FILTER = True  # XSS filter
SECURE_REFERRER_POLICY = 'strict-origin-when-cross-origin'  # Referrer policy

# Custom headers
SECURE_CONTENT_SECURITY_POLICY = "default-src 'self'"

Login Templates

<!-- registration/login.html -->
{% extends 'base.html' %}

{% block content %}
<div class="login-container">
    <h2>Login</h2>
    
    {% if form.errors %}
    <div class="error">
        <p>Your username and password didn't match. Please try again.</p>
    </div>
    {% endif %}
    
    {% if next %}
        {% if user.is_authenticated %}
        <p>Your account doesn't have access to this page.</p>
        {% else %}
        <p>Please login to see this page.</p>
        {% endif %}
    {% endif %}
    
    <form method="post" action="{% url 'login' %}">
        {% csrf_token %}
        
        <div class="form-group">
            <label for="id_username">Username</label>
            <input type="text" name="username" id="id_username" required>
        </div>
        
        <div class="form-group">
            <label for="id_password">Password</label>
            <input type="password" name="password" id="id_password" required>
        </div>
        
        <button type="submit">Login</button>
        <input type="hidden" name="next" value="{{ next }}">
    </form>
    
    <p><a href="{% url 'password_reset' %}">Forgot password?</a></p>
</div>
{% endblock %}

Best Practices

1. Always use {% csrf_token %} in POST forms
2. Use HTTPS in production (SECURE_SSL_REDIRECT = True)
3. Enable HSTS for secure connections
4. Set secure cookies (SESSION_COOKIE_SECURE = True)
5. Use strong password validation
6. Use @login_required for protected views
7. Never expose sensitive data in URLs or logs
8. Validate file uploads carefully
9. Use prepared statements (Django ORM does this automatically)

ORM Optimization

Avoiding Duplicate Objects with Exists Subquery

When filtering across relationships (one-to-many or many-to-many), JOINs produce duplicate parent objects:

# Problem: duplicates returned
Author.objects.filter(books__title__startswith="Book")
# [<Author: Charlie>, <Author: Alice>, <Author: Alice>]  # Alice appears twice

Solution: Use Exists Subquery (fastest, no ordering issues):

from django.db.models import Exists, OuterRef

Author.objects.filter(
    Exists(Book.objects.filter(
        author=OuterRef("id"),
        title__startswith="Book",
    ))
).order_by("name")

• Stops evaluation on first match
• No ordering restrictions
• Works with all databases

PostgreSQL-only alternative:

Author.objects.filter(books__title__startswith="Book").distinct("id")

N+1 Query Prevention

Problem:

for user in User.objects.all()[:100]:
    user.groups.count()  # 100 extra queries!

Solution: Use prefetch_related with Prefetch object:

from django.db.models import Prefetch

staff_groups = Group.objects.filter(name__in=["admin", "superuser"])
users = User.objects.prefetch_related(
    "groups",
    Prefetch("groups", to_attr="staff_groups", queryset=staff_groups),
).order_by("id")[:100]

for user in users:
    groups_total = user.groups.count()  # Uses cached data
    is_staff = len(user.staff_groups) > 0  # No new query!

Avoid querying prefetched objects unnecessarily:

# BAD: Makes new query
first_group = user.groups.first()

# GOOD: Uses in-memory data
first_group = user.groups.all()[0]

Time-Based Lookups Performance

Problem: timestamp__date lookup bypasses indexes:

# SLOW (30s on 25M rows)
Event.objects.filter(timestamp__date=datetime.date(2026, 1, 5))
# SQL: WHERE timestamp::date='2026-01-05'  # Full table scan!

Solution: Use range boundaries:

import datetime
start = datetime.datetime(2026, 1, 5, tzinfo=datetime.UTC)
end = start + datetime.timedelta(days=1)

Event.objects.filter(timestamp__gte=start, timestamp__lt=end)
# Uses index, drops to <1s

Deferring Large Fields

# Defer large fields you don't need
books = Book.objects.defer("content", "notes")

# Or explicitly load only needed fields
books = Book.objects.only("title", "pub_date")

Statement Timeouts (PostgreSQL)

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "mydb",
        "OPTIONS": {
            "options": "-c statement_timeout=30s",  # Terminate queries >30s
        },
    }
}

Django Tasks Framework (Django 6.0+)

Django 6.0 introduced a built-in tasks framework - an abstraction without a production-ready worker.

Define a Task

from django.tasks import task

@task(priority=2, queue_name="emails", backend="default")
def send_welcome_email(user_id):
    user = User.objects.get(id=user_id)
    send_mail("Welcome!", "Thanks for signing up.", "noreply@example.com", [user.email])

Parameters:

• priority (int): -100 to 100, defaults to 0
• queue_name (str): defaults to "default"
• backend (str): backend alias
• takes_context (bool): whether function accepts TaskContext

Enqueue the Task

# Synchronous
send_welcome_email.enqueue(user_id=user.id)

# Asynchronous
await send_welcome_email.aenqueue(user_id=user.id)

Built-in Backends (Development Only)

Production: django-tasks-local

# settings.py
INSTALLED_APPS = ["django_tasks_local"]

TASKS = {
    "default": {
        "BACKEND": "django_tasks_local.ThreadPoolBackend",
        "OPTIONS": {"MAX_WORKERS": 10}
    }
}

When to use Django Tasks vs Celery:

• Django Tasks: Fire-and-forget, no infrastructure (emails, webhooks, MVPs)
• Celery: Scheduled tasks, retries, persistence, distributed processing

Django Permissions

Custom Permissions in Model Meta

class Experiment(models.Model):
    name = models.CharField(max_length=100)
    
    class Meta:
        permissions = [
            ("change_experiment_status", "Can change status"),
            ("view_experiment_details", "Can view details"),
        ]

Groups for Role-Based Access

from django.contrib.auth.models import Group

# Create groups
read_only = Group.objects.create(name="Read only")
maintainer = Group.objects.create(name="Maintainer")

# Assign permission to group
maintainer.permissions.add(permission)

# Assign user to group
maintainer.user_set.add(user)

Function-Based View Protection

from django.contrib.auth.decorators import login_required, permission_required

@login_required
def my_view(request):
    ...

@permission_required("blog.view_post")
def restricted_view(request):
    ...

Class-Based View Protection

from django.contrib.auth.mixins import LoginRequiredMixin, PermissionRequiredMixin
from django.views.generic import TemplateView

class RestrictedView(LoginRequiredMixin, TemplateView):
    template_name = 'restricted.html'
    raise_exception = True

class PermissionView(PermissionRequiredMixin, TemplateView):
    permission_required = ('posts.can_edit', 'posts.can_view')
    template_name = 'permission_required.html'

Object-Level Permissions with Django Guardian

from guardian.shortcuts import assign_perm, remove_perm

# Assign object-level permission
assign_perm("change_post", user, post)
assign_perm("view_post", group, post)

# Check permission
user.has_perm("change_post", post)

Signal-Based Auto Permission Assignment

from django.db.models.signals import post_save
from django.dispatch import receiver
from guardian.shortcuts import assign_perm

@receiver(post_save, sender=Post)
def set_permission(sender, instance, **kwargs):
    assign_perm("change_post", instance.author, instance)
    assign_perm("view_post", instance.author, instance)

Caching

View Caching

from django.views.decorators.cache import cache_page

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

Template Fragment Caching

{% cache 300 my_cache_key %}
    <!-- Expensive content -->
{% endcache %}

Low-Level Cache API

from django.core.cache import cache

cache.set('my_key', 'my_value', timeout=3600)
value = cache.get('my_key')
cache.delete('my_key')

# Multiple keys
cache.set_many({'a': 1, 'b': 2}, timeout=300)
cache.get_many(['a', 'b'])

Redis Cache Backend

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.redis.RedisCache',
        'LOCATION': 'redis://127.0.0.1:6379/0',
    }
}

Testing Optimization

Fast Password Hashing for Tests

# settings.py
PASSWORD_HASHERS = [
    'django.contrib.auth.hashers.MD5PasswordHasher',  # 70% faster
]

Parallel Testing

python manage.py test --parallel

Capture on_commit Callbacks in Tests

from django.test import TestCase

class ContactTests(TestCase):
    def test_post(self):
        with self.captureOnCommitCallbacks(execute=True) as callbacks:
            response = self.client.post("/contact/", {"message": "Test"})
        
        self.assertEqual(len(callbacks), 1)  # Verify callback was enqueued

In-Memory SQLite for Tests

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'file::memory:',
    }
}

Assert Query Count

def test_something(self):
    with self.assertNumQueries(5):
        process_data()

Migrations

Squashing Migrations

# Squash migrations 0002 to 0006
python manage.py squashmigrations app 0002 0006

Then update dependencies in other migrations:

class Migration(migrations.Migration):
    dependencies = [
        ('app', '0007_squashed_0006'),  # Update to squashed migration
    ]

Standalone Django ORM (inspectdb)

Query existing databases without a full project:

# settings.py
import os
from django.conf import settings

settings.configure(
    DATABASES={"default": {"ENGINE": "django.db.backends.sqlite3", "NAME": "db.sqlite"}},
    INSTALLED_APPS=["myapp"],
)

# Generate models
# python manage.py inspectdb > models.py

Critical Model Attribute:

class Place(models.Model):
    url = models.URLField()
    title = models.CharField(null=True)
    
    class Meta:
        managed = False  # Don't try to create/migrate
        db_table = "moz_places"  # Existing table name

Django Signals Best Practices

Defining and Using Signals

# Define custom signals
from django.dispatch import Signal
user_logged_in = Signal(providing_args=['user', 'request'])

# Connect receivers with decorator
from django.dispatch import receiver
from django.contrib.auth.signals import user_logged_in

@receiver(user_logged_in)
def log_user_login(sender, user, request, **kwargs):
    ActivityLog.objects.create(
        user=user,
        event_type=ActivityLog.LOGIN,
        context={'ip': request.META.get('REMOTE_ADDR')}
    )

# Register in AppConfig.ready() to avoid circular imports
class MyAppConfig(AppConfig):
    def ready(self):
        import myapp.signals

Common Pitfalls to Avoid

• Heavy computations in signal handlers → Use Celery for async tasks
• Circular imports → Use string references: sender="myapp.MyModel"
• Duplicate connections → Use dispatch_uid parameter
• Not registering signals → Register in AppConfig.ready()

Field-Level Encryption

# Using django-secured-fields or django-fernet-encrypted-fields
from django_secured_fields.fields import EncryptedCharField

class UserProfile(models.Model):
    # Data encrypted at rest in database
    ssn = EncryptedCharField(max_length=11)
    credit_card = EncryptedCharField(max_length=16)
    
    # Transparent encryption/decryption via Django ORM
    # No manual encrypt/decrypt calls needed

Benefits:

• Field-level encryption (not blanket)
• Transparent integration with Django ORM
• Automatic key management
• Minimal performance impact

StreamingHttpResponse

For large responses, stream instead of loading entirely:

# Basic streaming response
def generate_csv():
    yield "Header1,Header2,Header3\n"
    yield "Value1,Value2,Value3\n"

def download_large_file(request):
    return StreamingHttpResponse(
        generate_csv(),
        content_type='text/csv'
    )

# For file downloads
from django.utils.filewrapper import FileWrapper

def download_file(request):
    file_like = open('large.csv', 'rb')
    return StreamingHttpResponse(
        FileWrapper(file_like),
        content_type='text/csv'
    )

Benefits:

• Lower memory usage (don't load entire file)
• Faster time-to-first-byte (TTFB)
• Better for large files (CSV, PDFs, exports)

Response Time Optimization

Use .only() to Limit Fields

# Before: Fetching 130+ fields
qs = Article.objects.all()

# After: Fetch only needed fields
qs = Article.objects.only(
    "headline", "slug", "summary",
    "publication_start_date", "image",
    "primary_category"
)

Denormalize Computed Fields

class Article(models.Model):
    def set_publication_order_date(self):
        if self.updated_at:
            self.publication_order_date = self.updated_at
        elif self.publication_start_date:
            self.publication_order_date = self.publication_start_date
    
    def save(self, *args, **kwargs):
        self.set_publication_order_date()
        super().save(*args, **kwargs)

Optimize Paginator Count

# Reduce count() query cost
qs.count = qs.only("id").count

Materialized Views with PostgreSQL

# Using django-materialized-view library
from django_materialized_view import MaterializedViewModel

class YearlyRuntimeModel(MaterializedViewModel):
    create_pkey_index = True
    year = models.IntegerField(primary_key=True)
    average_runtime = models.IntegerField()
    
    class Meta:
        managed = False  # Important!
    
    @staticmethod
    def get_query_from_queryset():
        return Movie.objects.values('year').annotate(
            average_runtime=Avg('runtime_minutes')
        )

# Create the view
python manage.py migrate_with_views

# Refresh when data changes
YearlyRuntimeModel.refresh()

Benefits:

• Speed up complex aggregations
• Cache expensive queries
• Refresh on schedule or triggers

pgvector Semantic Search

Vector similarity search with PostgreSQL and Django.

Setup

pip install pgvector sentence-transformers psycopg[binary]

# Migration to enable extension
from pgvector.django import VectorExtension

class Migration(migrations.Migration):
    operations = [VectorExtension()]

Model with Embeddings

from django.db import models
from pgvector.django import VectorField, CosineDistance
from sentence_transformers import SentenceTransformer

T = SentenceTransformer("distiluse-base-multilingual-cased-v1")

class Item(models.Model):
    content = models.TextField()
    embedding = VectorField(dimensions=512, editable=False)
    
    def save(self, *args, **kwargs):
        self.embedding = T.encode(self.content)
        super().save(*args, **kwargs)
    
    @classmethod
    def search(cls, q, dmax=0.5):
        distance = CosineDistance("embedding", T.encode(q))
        return (
            cls.objects.alias(distance=distance)
            .filter(distance__lt=dmax)
            .order_by(distance)
        )

# Usage
results = Item.search("python tutorial")

SQL Generated

SELECT * FROM items_item 
WHERE (embedding <=> '[vector]') < 0.5 
ORDER BY (embedding <=> '[vector]') ASC;

GeneratedField (Django 5.0+)

Database-generated columns that are computed by the DB when source fields change.

SQLite Examples

# Mathematical calculation
class Rectangle(models.Model):
    base = models.FloatField()
    height = models.FloatField()
    area = models.GeneratedField(
        expression=F("base") * F("height"),
        output_field=models.FloatField(),
        db_persist=True,
    )

# Conditional status
class Order(models.Model):
    creation = models.DateTimeField()
    payment = models.DateTimeField(null=True)
    status = models.GeneratedField(
        expression=Case(
            When(payment__isnull=False, then=Value("paid")),
            default=Value("created"),
        ),
        output_field=models.TextField(),
    )

# Date truncation
class Event(models.Model):
    start = models.DateTimeField()
    start_date = models.GeneratedField(
        expression=TruncDate("start"),
        output_field=models.DateField(),
    )

PostgreSQL Examples

# JSON key extraction
class Package(models.Model):
    slug = models.CharField()
    data = models.JSONField()
    version = models.GeneratedField(
        expression=F("data__info__version"),
        output_field=models.CharField(),
    )

# Full-text search vector
from django.contrib.postgres.search import SearchVector, SearchVectorField

class Quote(models.Model):
    author = models.CharField()
    text = models.TextField()
    search = models.GeneratedField(
        expression=SearchVector("text", config="english"),
        output_field=SearchVectorField(),
    )

# Array length
from django.contrib.postgres.fields import ArrayField, ArrayLenTransform

class Landmark(models.Model):
    name = models.CharField()
    reviews = ArrayField(models.SmallIntegerField())
    count = models.GeneratedField(
        expression=ArrayLenTransform("reviews"),
        output_field=models.IntegerField(),
    )

⚠️ Note: PostgreSQL requires IMMUTABLE functions only. Use || operator instead of Concat.

GeoDjango with Pillow and GPS

Build maps with automatic GPS extraction from photo EXIF data.

Setup

# settings.py
INSTALLED_APPS = ["django.contrib.gis", "markers"]

DATABASES = {
    "default": {
        "ENGINE": "django.contrib.gis.db.backends.spatialite",
        "NAME": BASE_DIR / "db.sqlite3",
    }
}

GPS Extraction from Images

from PIL import Image
from PIL.ExifTags import GPS, IFD
from django.contrib.gis.geos import Point

def dms_to_dd(degrees, minutes, seconds, ref):
    REFS = {"N": 1, "S": -1, "E": 1, "W": -1}
    return (float(degrees) + float(minutes)/60 + float(seconds)/3600) * REFS.get(ref, 0)

def get_point(image):
    gpsinfo = Image.open(image).getexif().get_ifd(IFD.GPSInfo)
    longitude = dms_to_dd(*gpsinfo.get(GPS.GPSLongitude, (0,0,0)), gpsinfo.get(GPS.GPSLongitudeRef, "E"))
    latitude = dms_to_dd(*gpsinfo.get(GPS.GPSLatitude, (0,0,0)), gpsinfo.get(GPS.GPSLatitudeRef, "N"))
    return Point(longitude, latitude)

Model with Auto-GPS

class Marker(models.Model):
    name = models.CharField()
    location = models.PointField(blank=True)
    image = models.ImageField(upload_to="images/markers/")

    def save(self, *args, **kwargs):
        self.location = get_point(self.image)
        super().save(*args, **kwargs)

Admin and GeoJSON

from django.contrib.gis import admin

@admin.register(Marker)
class MarkerAdmin(admin.GISModelAdmin):
    list_display = ("name", "location", "image")

# Serialize to GeoJSON
from django.core.serializers import serialize
import json

geojson = json.loads(serialize("geojson", Marker.objects.all()))

PostgreSQL Superpowers

Full-Text Search

from django.contrib.postgres.search import SearchQuery, SearchVector

# Simple search
results = Article.objects.annotate(
    search=SearchVector("title", "body")
).filter(search="django")

# With ranking
from django.contrib.postgres.search import SearchRank

results = Article.objects.annotate(
    rank=SearchRank(SearchVector("body"), SearchQuery("django"))
).order_by("-rank")

Array Fields

from django.contrib.postgres.fields import ArrayField

class Recipe(models.Model):
    name = models.CharField()
    tags = ArrayField(models.CharField(max_length=50))

# Query
Recipe.objects.filter(tags__contains=["vegan", "quick"])
Recipe.objects.filter(tags__overlap=["breakfast", "lunch"])

Range Fields

from django.contrib.postgres.fields import IntegerRangeField, DateRangeField

class Booking(models.Model):
    room = models.CharField()
    stay = DateRangeField()

# Overlap query
Booking.objects.filter(stay__overlap=[start_date, end_date])

JSONB Operations

class Product(models.Model):
    data = models.JSONField()

# Key existence
Product.objects.filter(data__has_key="specs")

# Path query
Product.objects.filter(data__specs__memory__gte=16)

Django 6.0 Essentials

Middleware Changes

• CommonMiddleware deprecated → Use StaticFileMiddleware for static file serving
• CSP nonce improvements - Built-in nonce support via {% csp_nonce %} template tag

Te

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