django-patterns

name	django-patterns
description	Django patterns — models, ORM, class-based views, middleware, URL routing, forms, project layout. Activate when writing or reviewing Django code.
origin	FlowDeck

Django Patterns Skill

Idiomatic Django for production systems. Covers models, views, ORM patterns, and project layout.

When to Activate

Activate when:

• Writing new Django apps or services
• Reviewing Django code for correctness and idiom
• Designing model relationships and ORM queries
• Building views with class-based views or function-based views
• Configuring URL routing and middleware

Project Structure

Standard Layout

manage.py
mysite/
    __init__.py
    settings.py
    urls.py
    wsgi.py
myapp/
    __init__.py
    models.py
    views.py
    urls.py
    admin.py
    apps.py

Decoupled Layout (Recommended)

manage.py
myapp/
    __init__.py
    models.py
    views.py
    urls.py
mysite/
    __init__.py
    settings.py
    urls.py
    wsgi.py

Import apps as top-level modules without project prefix.

Models and ORM

Basic Model Definition

from django.db import models

class Reporter(models.Model):
    full_name = models.CharField(max_length=70)

    def __str__(self):
        return self.full_name

class Article(models.Model):
    pub_date = models.DateField()
    headline = models.CharField(max_length=200)
    content = models.TextField()
    reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)

    def __str__(self):
        return self.headline

Field Types and Options

class Book(models.Model):
    class Status(models.TextChoices):
        DRAFT = 'draft', 'Draft'
        PUBLISHED = 'published', 'Published'
        ARCHIVED = 'archived', 'Archived'

    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name='books')
    isbn = models.CharField(max_length=13, unique=True)
    published_date = models.DateField()
    price = models.DecimalField(max_digits=10, decimal_places=2)
    status = models.CharField(max_length=10, choices=Status.choices, default=Status.DRAFT)
    tags = models.ManyToManyField('Tag', blank=True)

    class Meta:
        ordering = ['title']
        indexes = [
            models.Index(fields=['title', 'author']),
            models.Index(fields=['published_date']),
        ]

QuerySet Operations

# Create
author = Author.objects.create(name="Jane Doe", email="[e-mail]")
book = Book.objects.create(title="Django Mastery", author=author, isbn="9781234567890")

# Read with filtering
published_books = Book.objects.filter(status=Book.Status.PUBLISHED)
expensive_books = Book.objects.filter(price__gte=30.00)

# Complex queries with Q objects
from django.db.models import Q, F, Count, Avg
books = Book.objects.filter(
    Q(title__icontains='django') | Q(author__name__icontains='django')
).exclude(status=Book.Status.ARCHIVED)

# Aggregations
author_stats = Author.objects.annotate(
    book_count=Count('books'),
    avg_price=Avg('books__price')
).filter(book_count__gt=0)

# Update with F expressions
Book.objects.filter(pk=1).update(price=F('price') * 1.1)

# Select related (prevents N+1)
books_with_authors = Book.objects.select_related('author').all()

Views

Class-Based Views

from django.http import HttpResponse
from django.views import View
from django.views.generic import ListView, DetailView, CreateView

class MyView(View):
    def get(self, request, *args, **kwargs):
        return HttpResponse("Hello, World!")

# URL routing
from django.urls import path
urlpatterns = [
    path("about/", MyView.as_view()),
]

Generic Class-Based Views

class ArticleListView(ListView):
    model = Article
    template_name = "articles/list.html"
    context_object_name = "articles"

    def get_queryset(self):
        return Article.objects.filter(status='published').select_related('author')

class ArticleDetailView(DetailView):
    model = Article
    template_name = "articles/detail.html"
    context_object_name = "article"

class ArticleCreateView(CreateView):
    model = Article
    fields = ['title', 'content', 'author', 'status']
    template_name = "articles/form.html"
    success_url = reverse_lazy('article-list')

Function-Based Views

from django.http import JsonResponse
from django.shortcuts import get_object_or_404

def article_detail(request, pk):
    article = get_object_or_404(Article, pk=pk)
    return JsonResponse({
        'id': article.id,
        'title': article.title,
        'content': article.content,
    })

URL Routing

from django.urls import path, include

urlpatterns = [
    path("articles/", include("articles.urls")),
    path("about/", AboutView.as_view(), name="about"),
]

# In articles/urls.py
from django.urls import path
from .views import ArticleListView, ArticleDetailView

urlpatterns = [
    path("", ArticleListView.as_view(), name="article-list"),
    path("<int:pk>/", ArticleDetailView.as_view(), name="article-detail"),
]

Middleware

Function-Based Middleware

def simple_middleware(get_response):
    def middleware(request):
        # Code executed before view
        response = get_response(request)
        # Code executed after view
        return response
    return middleware

Adding to Settings

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'myapp.middleware.simple_middleware',
]

Forms

Model Forms

from django import forms
from .models import Article

class ArticleForm(forms.ModelForm):
    class Meta:
        model = Article
        fields = ['title', 'content', 'author', 'status']

    def clean_title(self):
        title = self.cleaned_data['title']
        if 'spam' in title.lower():
            raise forms.ValidationError("No spam allowed")
        return title

Common Pitfalls

N+1 Query Problem

# Bad: causes N+1 queries
articles = Article.objects.all()
for article in articles:
    print(article.author.name)  # N additional queries

# Good: use select_related or prefetch_related
articles = Article.objects.select_related('author').all()
for article in articles:
    print(article.author.name)  # No additional queries

Using Q Objects for Complex Queries

from django.db.models import Q

# OR conditions
Book.objects.filter(Q(title__icontains='django') | Q(author__name__icontains='django'))

# AND with exclusion
Book.objects.filter(status='published').exclude(Q(title__icontains='old'))

Bulk Operations

# Create multiple objects efficiently
Book.objects.bulk_create([
    Book(title='Book 1', author=author),
    Book(title='Book 2', author=author),
])

# Update multiple objects
Book.objects.filter(status='archived').update(status='published')

Related Skills

• django-tdd
• python-patterns
• api-design