Django

Django Framework Guide

Applies to: Django 5+, Django REST Framework, Django Channels Language: Python 3.10+

Core Principles

1. Batteries Included: Leverage Django's built-in features before adding third-party packages
2. DRY: Don't Repeat Yourself -- use abstract models, mixins, and shared utilities
3. Fat Models, Thin Views: Keep business logic in models and services, not views
4. Explicit Over Implicit: Use clear URL patterns, explicit imports, named relationships
5. Security by Default: CSRF, XSS protection, SQL injection prevention are built in

When to Use Django

Good fit:

• Full-stack web applications with templates
• Admin interface needed out of the box
• Content management systems
• Session-based authentication
• ORM with built-in migrations

Consider alternatives:

• Pure APIs with async-first needs (FastAPI)
• Minimal framework overhead (Flask)
• Real-time heavy workloads without Channels

Project Structure

myproject/
├── manage.py
├── pyproject.toml
├── requirements/
│   ├── base.txt
│   ├── dev.txt
│   └── prod.txt
├── config/                    # Project configuration
│   ├── __init__.py
│   ├── settings/
│   │   ├── __init__.py
│   │   ├── base.py
│   │   ├── dev.py
│   │   └── prod.py
│   ├── urls.py
│   ├── wsgi.py
│   └── asgi.py
├── apps/                      # Django applications
│   ├── users/
│   │   ├── __init__.py
│   │   ├── admin.py
│   │   ├── apps.py
│   │   ├── models.py
│   │   ├── views.py
│   │   ├── urls.py
│   │   ├── forms.py
│   │   ├── serializers.py     # If using DRF
│   │   ├── services.py        # Business logic
│   │   └── tests/
│   │       ├── __init__.py
│   │       ├── test_models.py
│   │       ├── test_views.py
│   │       └── test_services.py
│   └── core/                  # Shared utilities
│       ├── __init__.py
│       ├── models.py          # Abstract base models
│       └── mixins.py
├── templates/
│   ├── base.html
│   └── components/
├── static/
│   ├── css/
│   └── js/
└── tests/
    └── conftest.py

• Split settings into base.py, dev.py, prod.py
• Group apps under apps/ directory
• Keep core/ app for shared abstract models and utilities
• Place business logic in services.py, not in views
• Co-locate tests inside each app under tests/ directory

Guardrails

Settings

• Never hardcode SECRET_KEY -- use python-decouple or environment variables
• Split settings: base.py (shared), dev.py (debug), prod.py (secure)
• Always define AUTH_USER_MODEL before first migration
• Set DEFAULT_AUTO_FIELD = "django.db.models.BigAutoField"
• Use ALLOWED_HOSTS in production (never ["*"])

Models

• Always define __str__ on every model
• Always set class Meta with db_table, ordering, and indexes
• Use abstract base models for shared fields (TimeStampedModel, UUIDModel)
• Use TextChoices/IntegerChoices for status fields (not raw strings)
• Add related_name to all ForeignKey and OneToOneField relationships
• Use on_delete explicitly: CASCADE, PROTECT, SET_NULL, SET_DEFAULT
• Add database indexes for frequently queried fields
• Use validators at model level for domain constraints

Abstract Base Models

# apps/core/models.py
from django.db import models
import uuid


class TimeStampedModel(models.Model):
    """Abstract base with created/updated timestamps."""
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True


class UUIDModel(models.Model):
    """Abstract base with UUID primary key."""
    id = models.UUIDField(
        primary_key=True, default=uuid.uuid4, editable=False
    )

    class Meta:
        abstract = True

Custom User Model

• Always create a custom user model before the first migration
• Extend AbstractUser (not AbstractBaseUser unless you need full control)
• Set AUTH_USER_MODEL = "users.User" in settings

# apps/users/models.py
from django.contrib.auth.models import AbstractUser
from django.db import models
from apps.core.models import TimeStampedModel, UUIDModel


class User(AbstractUser, UUIDModel, TimeStampedModel):
    email = models.EmailField(unique=True)
    USERNAME_FIELD = "email"
    REQUIRED_FIELDS = ["username"]

    class Meta:
        db_table = "users"
        ordering = ["-created_at"]
        indexes = [models.Index(fields=["email"])]

    def __str__(self) -> str:
        return self.email

Views and URLs

Class-Based Views (CBVs)

• Use ListView, DetailView, CreateView, UpdateView for CRUD
• Use LoginRequiredMixin for authenticated views
• Override get_queryset() to add filtering and select_related/prefetch_related
• Override form_valid() to inject the current user

from django.views.generic import ListView
from django.db.models import Q
from .models import Product


class ProductListView(ListView):
    model = Product
    template_name = "products/list.html"
    context_object_name = "products"
    paginate_by = 20

    def get_queryset(self):
        qs = Product.objects.filter(
            status=Product.Status.PUBLISHED
        )
        search = self.request.GET.get("q")
        if search:
            qs = qs.filter(
                Q(name__icontains=search)
                | Q(description__icontains=search)
            )
        return qs.select_related("category")

URL Configuration

# config/urls.py
from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path("admin/", admin.site.urls),
    path("api/", include("apps.api.urls")),
    path("", include("apps.products.urls")),
]

• Use include() for app-level URL namespaces
• Use app_name in each app's urls.py for reverse resolution
• Serve media files in DEBUG mode only

ORM Essentials

Query Optimization

• Always use select_related() for ForeignKey/OneToOne (SQL JOIN)
• Always use prefetch_related() for ManyToMany/reverse FK (separate query)
• Use only() or defer() to limit fields when not all columns needed
• Never call Model.objects.all() without pagination or limits
• Use F() expressions for database-level operations
• Use Q() objects for complex lookups

Avoiding N+1 Queries

# BAD: N+1 queries
for product in Product.objects.all():
    print(product.category.name)  # Extra query per product

# GOOD: Single JOIN query
for product in Product.objects.select_related("category"):
    print(product.category.name)  # No extra queries

Transactions

• Use @transaction.atomic for multi-step writes
• Use select_for_update() for optimistic locking

from django.db import transaction

@transaction.atomic
def transfer_stock(source_id, dest_id, qty):
    source = Product.objects.select_for_update().get(id=source_id)
    dest = Product.objects.select_for_update().get(id=dest_id)
    source.stock -= qty
    dest.stock += qty
    source.save(update_fields=["stock"])
    dest.save(update_fields=["stock"])

Admin Configuration

from django.contrib import admin
from .models import Product

@admin.register(Product)
class ProductAdmin(admin.ModelAdmin):
    list_display = ["name", "category", "price", "status"]
    list_filter = ["status", "category", "created_at"]
    search_fields = ["name", "description"]
    prepopulated_fields = {"slug": ("name",)}
    readonly_fields = ["created_at", "updated_at"]
    ordering = ["-created_at"]

    fieldsets = (
        (None, {"fields": ("name", "slug", "description")}),
        ("Pricing", {"fields": ("price", "stock")}),
        ("Classification", {"fields": ("category", "status")}),
        ("Timestamps", {
            "fields": ("created_at", "updated_at"),
            "classes": ("collapse",),
        }),
    )

• Always register models with @admin.register(Model)
• Use list_display for useful columns, list_filter for filtering
• Use prepopulated_fields for slug generation
• Group fields with fieldsets for organized admin forms

Django REST Framework (DRF)

Settings

REST_FRAMEWORK = {
    "DEFAULT_AUTHENTICATION_CLASSES": [
        "rest_framework.authentication.SessionAuthentication",
        "rest_framework_simplejwt.authentication.JWTAuthentication",
    ],
    "DEFAULT_PERMISSION_CLASSES": [
        "rest_framework.permissions.IsAuthenticated",
    ],
    "DEFAULT_PAGINATION_CLASS": (
        "rest_framework.pagination.PageNumberPagination"
    ),
    "PAGE_SIZE": 20,
    "DEFAULT_THROTTLE_RATES": {
        "anon": "100/hour",
        "user": "1000/hour",
    },
}

ViewSets and Routers

• Use ModelViewSet for full CRUD
• Use @action(detail=True/False) for custom endpoints
• Override get_serializer_class() for different read/write serializers
• Override get_queryset() to add select_related/prefetch_related

from rest_framework import viewsets
from rest_framework.decorators import action
from rest_framework.response import Response


class ProductViewSet(viewsets.ModelViewSet):
    queryset = Product.objects.select_related("category")
    permission_classes = [IsAuthenticatedOrReadOnly]

    def get_serializer_class(self):
        if self.action in ["create", "update", "partial_update"]:
            return ProductCreateSerializer
        return ProductSerializer

    def perform_create(self, serializer):
        serializer.save(created_by=self.request.user)

    @action(detail=True, methods=["post"])
    def publish(self, request, pk=None):
        product = self.get_object()
        product.status = Product.Status.PUBLISHED
        product.save(update_fields=["status"])
        return Response({"status": "published"})

Serializers

• Use ModelSerializer for standard CRUD
• Add read_only_fields for computed/auto fields
• Validate in validate_<field>() or validate() methods
• Use nested serializers for read, flat IDs for write

Security Essentials

• CSRF: Enabled by default for forms; use @csrf_exempt sparingly
• XSS: Django templates auto-escape by default; never use |safe with user data
• SQL Injection: ORM uses parameterized queries; never use raw SQL with string formatting
• Clickjacking: X-Frame-Options middleware enabled by default
• HTTPS: Set SECURE_SSL_REDIRECT = True in production
• HSTS: Set SECURE_HSTS_SECONDS in production
• Cookies: Set SESSION_COOKIE_SECURE = True and CSRF_COOKIE_SECURE = True
• Passwords: Use AUTH_PASSWORD_VALIDATORS (enabled by default)
• CORS: Use django-cors-headers with explicit allowed origins (never CORS_ALLOW_ALL_ORIGINS in production)

Testing

Standards

• Use pytest with pytest-django (not Django's built-in test runner)
• Mark database tests with @pytest.mark.django_db
• Use factory-boy or fixtures for test data
• Use APIClient for DRF endpoint testing
• Coverage target: >80% for business logic
• Test file naming: test_models.py, test_views.py, test_services.py

Fixtures

# conftest.py
import pytest
from rest_framework.test import APIClient
from apps.users.models import User


@pytest.fixture
def api_client():
    return APIClient()


@pytest.fixture
def user(db):
    return User.objects.create_user(
        username="testuser",
        email="test@example.com",
        password="testpass123",
    )


@pytest.fixture
def authenticated_client(api_client, user):
    api_client.force_authenticate(user=user)
    return api_client

Commands Reference

# Development
python manage.py runserver
python manage.py shell_plus          # django-extensions

# Migrations
python manage.py makemigrations
python manage.py migrate
python manage.py showmigrations

# Testing
pytest
pytest -v --cov=apps --cov-report=html
pytest apps/products/ -k "test_create"

# Database
python manage.py dbshell
python manage.py dumpdata products > fixtures/products.json
python manage.py loaddata fixtures/products.json

# Static files
python manage.py collectstatic

# Celery
celery -A config worker -l info
celery -A config beat -l info

Dependencies

Base: Django>=5.0, djangorestframework, django-cors-headers, django-filter, djangorestframework-simplejwt, python-decouple, psycopg2-binary, whitenoise

Dev: pytest, pytest-django, pytest-cov, factory-boy, django-debug-toolbar, django-extensions, black, ruff, mypy, django-stubs

Best Practices

Do

• Use select_related and prefetch_related for every queryset
• Create indexes for frequently queried fields
• Use @transaction.atomic for multi-step operations
• Validate at both model level and serializer level
• Write services for business logic (not in views)
• Use signals sparingly (prefer explicit service calls)
• Cache expensive queries with Django cache framework
• Use environment variables for all configuration

Don't

• Put business logic in views
• Use raw SQL without parameterization
• Ignore N+1 query problems
• Store sensitive data in settings files
• Use Model.objects.all() without limits
• Skip migrations in production
• Use CORS_ALLOW_ALL_ORIGINS = True in production
• Use |safe template filter with user-provided data

Advanced Topics

For detailed code examples and advanced patterns, see:

• references/patterns.md -- DRF serializers, middleware, services, signals, Celery tasks, management commands, deployment, and testing patterns

External References

• Django Documentation
• Django REST Framework
• Two Scoops of Django
• Django Best Practices