Django Application

Django Application

Overview

Build comprehensive Django web applications with proper model design, view hierarchies, database operations, user authentication, and admin functionality following Django conventions and best practices.

When to Use

• Creating Django web applications
• Designing models and database schemas
• Implementing views and URL routing
• Building authentication systems
• Using Django ORM for database operations
• Creating admin interfaces and dashboards

Instructions

1. Django Project Setup

django-admin startproject myproject
cd myproject
python manage.py startapp users
python manage.py startapp products

2. Model Design with ORM

# users/models.py
from django.contrib.auth.models import AbstractUser
from django.db import models
from django.contrib.auth import get_user_model

class CustomUser(AbstractUser):
    ROLE_CHOICES = [
        ('admin', 'Administrator'),
        ('user', 'Regular User'),
    ]
    profile_picture = models.ImageField(upload_to='profiles/', null=True)
    role = models.CharField(max_length=20, choices=ROLE_CHOICES, default='user')
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ['-created_at']
        indexes = [
            models.Index(fields=['email']),
            models.Index(fields=['role']),
        ]

    def __str__(self):
        return self.email

# products/models.py
User = get_user_model()

class Product(models.Model):
    STATUS_CHOICES = [
        ('draft', 'Draft'),
        ('published', 'Published'),
    ]

    title = models.CharField(max_length=200, db_index=True)
    slug = models.SlugField(unique=True)
    description = models.TextField()
    price = models.DecimalField(max_digits=10, decimal_places=2)
    stock = models.PositiveIntegerField(default=0)
    status = models.CharField(max_length=10, choices=STATUS_CHOICES, default='draft')
    owner = models.ForeignKey(User, related_name='products')
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ['-created_at']
        unique_together = ['slug', 'owner']

    def __str__(self):
        return self.title

class ProductReview(models.Model):
    product = models.ForeignKey(Product, related_name='reviews')
    author = models.ForeignKey(User,
    rating = models.IntegerField(choices=[(i, i) for i in range(1, 6)])
    comment = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        unique_together = ['product', 'author']

3. Views with Class-Based and Function-Based Approaches

# products/views.py
from django.views import View
from django.views.generic import ListView, DetailView, CreateView
from django.contrib.auth.mixins import LoginRequiredMixin
from django.shortcuts import render, redirect, get_object_or_404
from django.http import JsonResponse
from django.db.models import Q, Count, Avg
from rest_framework import viewsets, status
from rest_framework.response import Response
from rest_framework.decorators import action
from rest_framework.permissions import IsAuthenticated

from .models import Product, ProductReview
from .serializers import ProductSerializer

# Class-based view with authentication
class ProductListView(LoginRequiredMixin, ListView):
    model = Product
    template_name = 'products/list.html'
    context_object_name = 'products'
    paginate_by = 20

    def get_queryset(self):
        queryset = Product.objects.filter(status='published')

        # Search and filter
        search = self.request.GET.get('q')
        if search:
            queryset = queryset.filter(
                Q(title__icontains=search) | Q(description__icontains=search)
            )

        # Price range filter
        min_price = self.request.GET.get('min_price')
        max_price = self.request.GET.get('max_price')
        if min_price:
            queryset = queryset.filter(price__gte=min_price)
        if max_price:
            queryset = queryset.filter(price__lte=max_price)

        return queryset.annotate(
            review_count=Count('reviews'),
            avg_rating=Avg('reviews__rating')
        ).order_by('-created_at')

# REST API ViewSet
class ProductViewSet(viewsets.ModelViewSet):
    permission_classes = [IsAuthenticated]
    serializer_class = ProductSerializer
    queryset = Product.objects.all()

    def get_queryset(self):
        return Product.objects.filter(owner=self.request.user)

    @action(detail=True, methods=['post'])
    def add_review(self, request, pk=None):
        product = self.get_object()
        serializer = ProductReviewSerializer(data=request.data)

        if serializer.is_valid():
            serializer.save(product=product, author=request.user)
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    @action(detail=True, methods=['get'])
    def reviews(self, request, pk=None):
        product = self.get_object()
        reviews = product.reviews.all()
        serializer = ProductReviewSerializer(reviews, many=True)
        return Response(serializer.data)

4. Authentication and Permissions

# users/views.py
from django.contrib.auth import authenticate, login, logout
from django.views.decorators.http import require_http_methods
from django.views.decorators.csrf import csrf_protect
from rest_framework.authtoken.models import Token
from rest_framework.permissions import BasePermission

class IsOwner(BasePermission):
    def has_object_permission(self, request, view, obj):
        return obj.owner == request.user

@require_http_methods(['POST'])
@csrf_protect
def login_view(request):
    email = request.POST.get('email')
    password = request.POST.get('password')
    user = authenticate(request, username=email, password=password)

    if user is not None:
        login(request, user)
        token, created = Token.objects.get_or_create(user=user)
        return JsonResponse({
            'success': True,
            'token': token.key,
            'user_id': user.id
        })

    return JsonResponse({'error': 'Invalid credentials'}, status=401)

@require_http_methods(['POST'])
def logout_view(request):
    logout(request)
    return JsonResponse({'success': True})

5. Database Queries and Optimization

# products/queries.py
from django.db.models import Q, Count, Avg, F, Case, When, Value
from django.db.models.functions import Coalesce
from .models import Product, ProductReview

# Optimized queries with select_related and prefetch_related
def get_product_details(product_id):
    return Product.objects.select_related('owner').prefetch_related(
        'reviews__author'
    ).get(id=product_id)

# Aggregation queries
def get_top_products():
    return Product.objects.annotate(
        review_count=Count('reviews'),
        avg_rating=Avg('reviews__rating'),
        total_reviews=Count('reviews', distinct=True)
    ).filter(review_count__gt=0).order_by('-avg_rating')[:10]

# Complex filtering
def search_products(query, category=None, min_price=None, max_price=None):
    queryset = Product.objects.filter(
        Q(title__icontains=query) | Q(description__icontains=query)
    )

    if category:
        queryset = queryset.filter(category=category)
    if min_price:
        queryset = queryset.filter(price__gte=min_price)
    if max_price:
        queryset = queryset.filter(price__lte=max_price)

    return queryset.select_related('owner')

# Bulk operations
def bulk_update_stock(updates):
    products_to_update = []
    for product_id, new_stock in updates.items():
        product = Product.objects.get(id=product_id)
        product.stock = new_stock
        products_to_update.append(product)

    Product.objects.bulk_update(products_to_update, ['stock'])

6. URL Routing

# myproject/urls.py
from django.contrib import admin
from django.urls import path, include
from rest_framework.routers import DefaultRouter
from rest_framework.authtoken.views import obtain_auth_token
from products.views import ProductViewSet

router = DefaultRouter()
router.register(r'products', ProductViewSet)

urlpatterns = [
    path('admin/', admin.site.urls),
    path('api/', include(router.urls)),
    path('api-token-auth/', obtain_auth_token),
]

7. Admin Interface Customization

# products/admin.py
from django.contrib import admin
from .models import Product, ProductReview

@admin.register(Product)
class ProductAdmin(admin.ModelAdmin):
    list_display = ['title', 'price', 'stock', 'status', 'owner', 'created_at']
    list_filter = ['status', 'created_at', 'owner']
    search_fields = ['title', 'description']
    readonly_fields = ['created_at', 'updated_at']
    fieldsets = (
        ('Basic Info', {
            'fields': ('title', 'slug', 'owner')
        }),
        ('Details', {
            'fields': ('description', 'price', 'stock', 'status')
        }),
        ('Metadata', {
            'fields': ('created_at', 'updated_at'),
            'classes': ('collapse',)
        }),
    )

    def save_model(self, request, obj, form, change):
        if not change:
            obj.owner = request.user
        super().save_model(request, obj, form, change)

@admin.register(ProductReview)
class ProductReviewAdmin(admin.ModelAdmin):
    list_display = ['product', 'author', 'rating', 'created_at']
    list_filter = ['rating', 'created_at']
    readonly_fields = ['created_at']

Best Practices

✅ DO

• Use models for database operations
• Implement proper indexes on frequently queried fields
• Use select_related and prefetch_related for query optimization
• Implement authentication and permissions
• Use Django Forms for form validation
• Cache expensive queries
• Use management commands for batch operations
• Implement logging for debugging
• Use middleware for cross-cutting concerns
• Validate user input

❌ DON'T

• Use raw SQL without ORM
• N+1 query problems without optimization
• Store secrets in code
• Trust user input directly
• Override init in models unnecessarily
• Make synchronous heavy operations in views
• Use inheritance models unless necessary
• Expose stack traces in production

Complete Example

# settings.py
INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'rest_framework',
    'users',
    'products'
]

AUTH_USER_MODEL = 'users.CustomUser'

REST_FRAMEWORK = {
    'DEFAULT_AUTHENTICATION_CLASSES': [
        'rest_framework.authentication.TokenAuthentication',
    ],
    'DEFAULT_PERMISSION_CLASSES': [
        'rest_framework.permissions.IsAuthenticated',
    ]
}

# models.py + views.py (see sections above)
# urls.py + admin.py (see sections above)