Django Development Patterns

Production-grade Django architecture patterns for scalable, maintainable applications.

When to Activate

• Building Django web applications

• Designing Django REST Framework APIs

• Working with Django ORM and models

• Setting up Django project structure

• Implementing caching, signals, middleware

Project Structure

Recommended Layout

myproject/

├── config/

│   ├── __init__.py

│   ├── settings/

│   │   ├── __init__.py

│   │   ├── base.py          # Base settings

│   │   ├── development.py   # Dev settings

│   │   ├── production.py    # Production settings

│   │   └── test.py          # Test settings

│   ├── urls.py

│   ├── wsgi.py

│   └── asgi.py

├── manage.py

└── apps/

    ├── __init__.py

    ├── users/

    │   ├── __init__.py

    │   ├── models.py

    │   ├── views.py

    │   ├── serializers.py

    │   ├── urls.py

    │   ├── permissions.py

    │   ├── filters.py

    │   ├── services.py

    │   └── tests/

    └── products/

        └── ...

Split Settings Pattern

# config/settings/base.py

from pathlib import Path

BASE_DIR = Path(__file__).resolve().parent.parent.parent

SECRET_KEY = env('DJANGO_SECRET_KEY')

DEBUG = False

ALLOWED_HOSTS = []

INSTALLED_APPS = [

    'django.contrib.admin',

    'django.contrib.auth',

    'django.contrib.contenttypes',

    'django.contrib.sessions',

    'django.contrib.messages',

    'django.contrib.staticfiles',

    'rest_framework',

    'rest_framework.authtoken',

    'corsheaders',

    # Local apps

    'apps.users',

    'apps.products',

]

MIDDLEWARE = [

    'django.middleware.security.SecurityMiddleware',

    'whitenoise.middleware.WhiteNoiseMiddleware',

    'django.contrib.sessions.middleware.SessionMiddleware',

    'corsheaders.middleware.CorsMiddleware',

    'django.middleware.common.CommonMiddleware',

    'django.middleware.csrf.CsrfViewMiddleware',

    'django.contrib.auth.middleware.AuthenticationMiddleware',

    'django.contrib.messages.middleware.MessageMiddleware',

    'django.middleware.clickjacking.XFrameOptionsMiddleware',

]

ROOT_URLCONF = 'config.urls'

WSGI_APPLICATION = 'config.wsgi.application'

DATABASES = {

    'default': {

        'ENGINE': 'django.db.backends.postgresql',

        'NAME': env('DB_NAME'),

        'USER': env('DB_USER'),

        'PASSWORD': env('DB_PASSWORD'),

        'HOST': env('DB_HOST'),

        'PORT': env('DB_PORT', default='5432'),

    }

}

# config/settings/development.py

from .base import *

DEBUG = True

ALLOWED_HOSTS = ['localhost', '127.0.0.1']

DATABASES['default']['NAME'] = 'myproject_dev'

INSTALLED_APPS += ['debug_toolbar']

MIDDLEWARE += ['debug_toolbar.middleware.DebugToolbarMiddleware']

EMAIL_BACKEND = 'django.core.mail.backends.console.EmailBackend'

# config/settings/production.py

from .base import *

DEBUG = False

ALLOWED_HOSTS = env.list('ALLOWED_HOSTS')

SECURE_SSL_REDIRECT = True

SESSION_COOKIE_SECURE = True

CSRF_COOKIE_SECURE = True

SECURE_HSTS_SECONDS = 31536000

SECURE_HSTS_INCLUDE_SUBDOMAINS = True

SECURE_HSTS_PRELOAD = True

# Logging

LOGGING = {

    'version': 1,

    'disable_existing_loggers': False,

    'handlers': {

        'file': {

            'level': 'WARNING',

            'class': 'logging.FileHandler',

            'filename': '/var/log/django/django.log',

        },

    },

    'loggers': {

        'django': {

            'handlers': ['file'],

            'level': 'WARNING',

            'propagate': True,

        },

    },

}

Model Design Patterns

Model Best Practices

from django.db import models

from django.contrib.auth.models import AbstractUser

from django.core.validators import MinValueValidator, MaxValueValidator

class User(AbstractUser):

    """Custom user model extending AbstractUser."""

    email = models.EmailField(unique=True)

    phone = models.CharField(max_length=20, blank=True)

    birth_date = models.DateField(null=True, blank=True)

    USERNAME_FIELD = 'email'

    REQUIRED_FIELDS = ['username']

    class Meta:

        db_table = 'users'

        verbose_name = 'user'

        verbose_name_plural = 'users'

        ordering = ['-date_joined']

    def __str__(self):

        return self.email

    def get_full_name(self):

        return f"{self.first_name} {self.last_name}".strip()

class Product(models.Model):

    """Product model with proper field configuration."""

    name = models.CharField(max_length=200)

    slug = models.SlugField(unique=True, max_length=250)

    description = models.TextField(blank=True)

    price = models.DecimalField(

        max_digits=10,

        decimal_places=2,

        validators=[MinValueValidator(0)]

    )

    stock = models.PositiveIntegerField(default=0)

    is_active = models.BooleanField(default=True)

    category = models.ForeignKey(

        'Category',

        on_delete=models.CASCADE,

        related_name='products'

    )

    tags = models.ManyToManyField('Tag', blank=True, related_name='products')

    created_at = models.DateTimeField(auto_now_add=True)

    updated_at = models.DateTimeField(auto_now=True)

    class Meta:

        db_table = 'products'

        ordering = ['-created_at']

        indexes = [

            models.Index(fields=['slug']),

            models.Index(fields=['-created_at']),

            models.Index(fields=['category', 'is_active']),

        ]

        constraints = [

            models.CheckConstraint(

                check=models.Q(price__gte=0),

                name='price_non_negative'

            )

        ]

    def __str__(self):

        return self.name

    def save(self, *args, **kwargs):

        if not self.slug:

            self.slug = slugify(self.name)

        super().save(*args, **kwargs)

QuerySet Best Practices

from django.db import models

class ProductQuerySet(models.QuerySet):

    """Custom QuerySet for Product model."""

    def active(self):

        """Return only active products."""

        return self.filter(is_active=True)

    def with_category(self):

        """Select related category to avoid N+1 queries."""

        return self.select_related('category')

    def with_tags(self):

        """Prefetch tags for many-to-many relationship."""

        return self.prefetch_related('tags')

    def in_stock(self):

        """Return products with stock > 0."""

        return self.filter(stock__gt=0)

    def search(self, query):

        """Search products by name or description."""

        return self.filter(

            models.Q(name__icontains=query) |

            models.Q(description__icontains=query)

        )

class Product(models.Model):

    # ... fields ...

    objects = ProductQuerySet.as_manager()  # Use custom QuerySet

# Usage

Product.objects.active().with_category().in_stock()

Manager Methods

class ProductManager(models.Manager):

    """Custom manager for complex queries."""

    def get_or_none(self, **kwargs):

        """Return object or None instead of DoesNotExist."""

        try:

            return self.get(**kwargs)

        except self.model.DoesNotExist:

            return None

    def create_with_tags(self, name, price, tag_names):

        """Create product with associated tags."""

        product = self.create(name=name, price=price)

        tags = [Tag.objects.get_or_create(name=name)[0] for name in tag_names]

        product.tags.set(tags)

        return product

    def bulk_update_stock(self, product_ids, quantity):

        """Bulk update stock for multiple products."""

        return self.filter(id__in=product_ids).update(stock=quantity)

# In model

class Product(models.Model):

    # ... fields ...

    custom = ProductManager()

Django REST Framework Patterns

Serializer Patterns

from rest_framework import serializers

from django.contrib.auth.password_validation import validate_password

from .models import Product, User

class ProductSerializer(serializers.ModelSerializer):

    """Serializer for Product model."""

    category_name = serializers.CharField(source='category.name', read_only=True)

    average_rating = serializers.FloatField(read_only=True)

    discount_price = serializers.SerializerMethodField()

    class Meta:

        model = Product

        fields = [

            'id', 'name', 'slug', 'description', 'price',

            'discount_price', 'stock', 'category_name',

            'average_rating', 'created_at'

        ]

        read_only_fields = ['id', 'slug', 'created_at']

    def get_discount_price(self, obj):

        """Calculate discount price if applicable."""

        if hasattr(obj, 'discount') and obj.discount:

            return obj.price * (1 - obj.discount.percent / 100)

        return obj.price

    def validate_price(self, value):

        """Ensure price is non-negative."""

        if value < 0:

            raise serializers.ValidationError("Price cannot be negative.")

        return value

class ProductCreateSerializer(serializers.ModelSerializer):

    """Serializer for creating products."""

    class Meta:

        model = Product

        fields = ['name', 'description', 'price', 'stock', 'category']

    def validate(self, data):

        """Custom validation for multiple fields."""

        if data['price'] > 10000 and data['stock'] > 100:

            raise serializers.ValidationError(

                "Cannot have high-value products with large stock."

            )

        return data

class UserRegistrationSerializer(serializers.ModelSerializer):

    """Serializer for user registration."""

    password = serializers.CharField(

        write_only=True,

        required=True,

        validators=[validate_password],

        style={'input_type': 'password'}

    )

    password_confirm = serializers.CharField(write_only=True, style={'input_type': 'password'})

    class Meta:

        model = User

        fields = ['email', 'username', 'password', 'password_confirm']

    def validate(self, data):

        """Validate passwords match."""

        if data['password'] != data['password_confirm']:

            raise serializers.ValidationError({

                "password_confirm": "Password fields didn't match."

            })

        return data

    def create(self, validated_data):

        """Create user with hashed password."""

        validated_data.pop('password_confirm')

        password = validated_data.pop('password')

        user = User.objects.create(**validated_data)

        user.set_password(password)

        user.save()

        return user

ViewSet Patterns

from rest_framework import viewsets, status, filters

from rest_framework.decorators import action

from rest_framework.response import Response

from rest_framework.permissions import IsAuthenticated, IsAdminUser

from django_filters.rest_framework import DjangoFilterBackend

from .models import Product

from .serializers import ProductSerializer, ProductCreateSerializer

from .permissions import IsOwnerOrReadOnly

from .filters import ProductFilter

from .services import ProductService

class ProductViewSet(viewsets.ModelViewSet):

    """ViewSet for Product model."""

    queryset = Product.objects.select_related('category').prefetch_related('tags')

    permission_classes = [IsAuthenticated, IsOwnerOrReadOnly]

    filter_backends = [DjangoFilterBackend, filters.SearchFilter, filters.OrderingFilter]

    filterset_class = ProductFilter

    search_fields = ['name', 'description']

    ordering_fields = ['price', 'created_at', 'name']

    ordering = ['-created_at']

    def get_serializer_class(self):

        """Return appropriate serializer based on action."""

        if self.action == 'create':

            return ProductCreateSerializer

        return ProductSerializer

    def perform_create(self, serializer):

        """Save with user context."""

        serializer.save(created_by=self.request.user)

    @action(detail=False, methods=['get'])

    def featured(self, request):

        """Return featured products."""

        featured = self.queryset.filter(is_featured=True)[:10]

        serializer = self.get_serializer(featured, many=True)

        return Response(serializer.data)

    @action(detail=True, methods=['post'])

    def purchase(self, request, pk=None):

        """Purchase a product."""

        product = self.get_object()

        service = ProductService()

        result = service.purchase(product, request.user)

        return Response(result, status=status.HTTP_201_CREATED)

    @action(detail=False, methods=['get'], permission_classes=[IsAuthenticated])

    def my_products(self, request):

        """Return products created by current user."""

        products = self.queryset.filter(created_by=request.user)

        page = self.paginate_queryset(products)

        serializer = self.get_serializer(page, many=True)

        return self.get_paginated_response(serializer.data)

Custom Actions

from rest_framework.decorators import api_view, permission_classes

from rest_framework.permissions import IsAuthenticated

from rest_framework.response import Response

@api_view(['POST'])

@permission_classes([IsAuthenticated])

def add_to_cart(request):

    """Add product to user cart."""

    product_id = request.data.get('product_id')

    quantity = request.data.get('quantity', 1)

    try:

        product = Product.objects.get(id=product_id)

    except Product.DoesNotExist:

        return Response(

            {'error': 'Product not found'},

            status=status.HTTP_404_NOT_FOUND

        )

    cart, _ = Cart.objects.get_or_create(user=request.user)

    CartItem.objects.create(

        cart=cart,

        product=product,

        quantity=quantity

    )

    return Response({'message': 'Added to cart'}, status=status.HTTP_201_CREATED)

Service Layer Pattern

# apps/orders/services.py

from typing import Optional

from django.db import transaction

from .models import Order, OrderItem

class OrderService:

    """Service layer for order-related business logic."""

    @staticmethod

    @transaction.atomic

    def create_order(user, cart: Cart) -> Order:

        """Create order from cart."""

        order = Order.objects.create(

            user=user,

            total_price=cart.total_price

        )

        for item in cart.items.all():

            OrderItem.objects.create(

                order=order,

                product=item.product,

                quantity=item.quantity,

                price=item.product.price

            )

        # Clear cart

        cart.items.all().delete()

        return order

    @staticmethod

    def process_payment(order: Order, payment_data: dict) -> bool:

        """Process payment for order."""

        # Integration with payment gateway

        payment = PaymentGateway.charge(

            amount=order.total_price,

            token=payment_data['token']

        )

        if payment.success:

            order.status = Order.Status.PAID

            order.save()

            # Send confirmation email

            OrderService.send_confirmation_email(order)

            return True

        return False

    @staticmethod

    def send_confirmation_email(order: Order):

        """Send order confirmation email."""

        # Email sending logic

        pass

Caching Strategies

View-Level Caching

from django.views.decorators.cache import cache_page

from django.utils.decorators import method_decorator

@method_decorator(cache_page(60 * 15), name='dispatch')  # 15 minutes

class ProductListView(generic.ListView):

    model = Product

    template_name = 'products/list.html'

    context_object_name = 'products'

Template Fragment Caching

{% load cache %}

{% cache 500 sidebar %}

    ... expensive sidebar content ...

{% endcache %}

Low-Level Caching

from django.core.cache import cache

def get_featured_products():

    """Get featured products with caching."""

    cache_key = 'featured_products'

    products = cache.get(cache_key)

    if products is None:

        products = list(Product.objects.filter(is_featured=True))

        cache.set(cache_key, products, timeout=60 * 15)  # 15 minutes

    return products

QuerySet Caching

from django.core.cache import cache

def get_popular_categories():

    cache_key = 'popular_categories'

    categories = cache.get(cache_key)

    if categories is None:

        categories = list(Category.objects.annotate(

            product_count=Count('products')

        ).filter(product_count__gt=10).order_by('-product_count')[:20])

        cache.set(cache_key, categories, timeout=60 * 60)  # 1 hour

    return categories

Signals

Signal Patterns

# apps/users/signals.py

from django.db.models.signals import post_save

from django.dispatch import receiver

from django.contrib.auth import get_user_model

from .models import Profile

User = get_user_model()

@receiver(post_save, sender=User)

def create_user_profile(sender, instance, created, **kwargs):

    """Create profile when user is created."""

    if created:

        Profile.objects.create(user=instance)

@receiver(post_save, sender=User)

def save_user_profile(sender, instance, **kwargs):

    """Save profile when user is saved."""

    instance.profile.save()

# apps/users/apps.py

from django.apps import AppConfig

class UsersConfig(AppConfig):

    default_auto_field = 'django.db.models.BigAutoField'

    name = 'apps.users'

    def ready(self):

        """Import signals when app is ready."""

        import apps.users.signals

Middleware

Custom Middleware

# middleware/active_user_middleware.py

import time

from django.utils.deprecation import MiddlewareMixin

class ActiveUserMiddleware(MiddlewareMixin):

    """Middleware to track active users."""

    def process_request(self, request):

        """Process incoming request."""

        if request.user.is_authenticated:

            # Update last active time

            request.user.last_active = timezone.now()

            request.user.save(update_fields=['last_active'])

class RequestLoggingMiddleware(MiddlewareMixin):

    """Middleware for logging requests."""

    def process_request(self, request):

        """Log request start time."""

        request.start_time = time.time()

    def process_response(self, request, response):

        """Log request duration."""

        if hasattr(request, 'start_time'):

            duration = time.time() - request.start_time

            logger.info(f'{request.method} {request.path} - {response.status_code} - {duration:.3f}s')

        return response

Performance Optimization

N+1 Query Prevention

# Bad - N+1 queries

products = Product.objects.all()

for product in products:

    print(product.category.name)  # Separate query for each product

# Good - Single query with select_related

products = Product.objects.select_related('category').all()

for product in products:

    print(product.category.name)

# Good - Prefetch for many-to-many

products = Product.objects.prefetch_related('tags').all()

for product in products:

    for tag in product.tags.all():

        print(tag.name)

Database Indexing

class Product(models.Model):

    name = models.CharField(max_length=200, db_index=True)

    slug = models.SlugField(unique=True)

    category = models.ForeignKey('Category', on_delete=models.CASCADE)

    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:

        indexes = [

            models.Index(fields=['name']),

            models.Index(fields=['-created_at']),

            models.Index(fields=['category', 'created_at']),

        ]

Bulk Operations

# Bulk create

Product.objects.bulk_create([

    Product(name=f'Product {i}', price=10.00)

    for i in range(1000)

])

# Bulk update

products = Product.objects.all()[:100]

for product in products:

    product.is_active = True

Product.objects.bulk_update(products, ['is_active'])

# Bulk delete

Product.objects.filter(stock=0).delete()

Quick Reference

Remember: Django provides many shortcuts, but for production applications, structure and organization matter more than concise code. Build for maintainability.