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
myproject/
├── config/
│ ├── settings/
│ │ ├── 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/
├── users/
│ ├── models.py
│ ├── views.py
│ ├── serializers.py
│ ├── urls.py
│ ├── permissions.py
│ ├── services.py
│ └── tests/
└── products/
Model Design
from django.db import models
from django.core.validators import MinValueValidator
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()
Django REST Framework
Serializer Patterns
from rest_framework import serializers
from .models import Product
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
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
from django_filters.rest_framework import DjangoFilterBackend
class ProductViewSet(viewsets.ModelViewSet):
"""ViewSet for Product model."""
queryset = Product.objects.select_related('category').prefetch_related('tags')
permission_classes = [IsAuthenticated]
filter_backends = [DjangoFilterBackend, filters.SearchFilter, filters.OrderingFilter]
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)
Service Layer Pattern
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
Caching Strategies
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
from django.db.models import Count
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
Performance Optimization
N+1 Query Prevention
# N+1 queries
products = Product.objects.all()
for product in products:
print(product.category.name) # Separate query for each product
# Single query with select_related
products = Product.objects.select_related('category').all()
for product in products:
print(product.category.name)
# 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)
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()
Django provides many shortcuts, but for production applications, structure and organization matter more than concise code. Build for maintainability.