django-patterns

# Django Development Patterns Production-grade Django architecture patterns for scalable, maintainable applications. ## When to Use - 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 ```python # 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 ```python 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 ```python 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 ```python 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 ```python 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 ```python 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)