Django Guide

Guide Django

1. Choisir l'architecture

2. Initialiser le projet

pip install django djangorestframework django-environ
django-admin startproject config .   # config = dossier settings
python manage.py startapp orders     # une app par domaine métier

Structure recommandée :

project/
  config/
    settings/
      base.py      # commun
      dev.py       # DEBUG=True, SQLite
      prod.py      # ALLOWED_HOSTS, DATABASES Postgres, STATIC_ROOT
    urls.py
    wsgi.py
  orders/
    models.py
    views.py
    serializers.py
    urls.py
    admin.py
    tests/
  manage.py
  .env

config/settings/base.py :

from environ import Env
env = Env()
Env.read_env()

SECRET_KEY = env("SECRET_KEY")
DATABASES = {"default": env.db()}  # DATABASE_URL=postgres://...

3. Concevoir les models

from django.db import models
from django.utils.translation import gettext_lazy as _

class Order(models.Model):
    class Status(models.TextChoices):
        PENDING  = "pending",  _("En attente")
        SHIPPED  = "shipped",  _("Expédié")

    reference   = models.CharField(max_length=32, unique=True)
    customer    = models.ForeignKey("users.User",
                                    related_name="orders")
    status      = models.CharField(max_length=16, choices=Status.choices,
                                    default=Status.PENDING)
    created_at  = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ["-created_at"]
        indexes  = [models.Index(fields=["status", "created_at"])]

    def __str__(self):
        return f"Order {self.reference}"

    def clean(self):
        # Validation métier centralisée ici, pas dans la vue
        if self.status == self.Status.SHIPPED and not self.reference:
            raise ValidationError("Reference requise avant expédition.")

Migrations :

python manage.py makemigrations orders
python manage.py migrate
# Data migration
python manage.py makemigrations orders --empty --name backfill_reference

Data migration réversible :

def forwards(apps, schema_editor):
    Order = apps.get_model("orders", "Order")
    Order.objects.filter(reference="").update(reference="LEGACY")

def backwards(apps, schema_editor):
    pass  # irréversible acceptable si documenté

class Migration(migrations.Migration):
    operations = [migrations.RunPython(forwards, backwards)]

4. ORM — éviter le N+1

# MAL — N+1
orders = Order.objects.all()
for o in orders:
    print(o.customer.email)  # 1 requête par ligne

# BIEN
orders = Order.objects.select_related("customer").all()

# Relations M2M
orders = Order.objects.prefetch_related("items__product").all()

# Annoter en base plutôt que Python
from django.db.models import Count, Sum
Order.objects.annotate(total=Sum("items__price")).filter(total__gt=100)

5. DRF — sérializers et ViewSets

# serializers.py
class OrderSerializer(serializers.ModelSerializer):
    customer_email = serializers.EmailField(source="customer.email", read_only=True)

    class Meta:
        model  = Order
        fields = ["id", "reference", "status", "customer_email", "created_at"]
        read_only_fields = ["created_at"]

    def validate_status(self, value):
        allowed = ["pending", "shipped"]
        if value not in allowed:
            raise serializers.ValidationError(f"Statut invalide. Valeurs : {allowed}")
        return value

# views.py
from rest_framework import viewsets, permissions, filters
from django_filters.rest_framework import DjangoFilterBackend

class OrderViewSet(viewsets.ModelViewSet):
    serializer_class   = OrderSerializer
    permission_classes = [permissions.IsAuthenticated]
    filter_backends    = [DjangoFilterBackend, filters.OrderingFilter]
    filterset_fields   = ["status"]
    ordering_fields    = ["created_at"]

    def get_queryset(self):
        return Order.objects.select_related("customer")\
                            .filter(customer=self.request.user)

    def perform_create(self, serializer):
        serializer.save(customer=self.request.user)

# urls.py (app)
from rest_framework.routers import DefaultRouter
router = DefaultRouter()
router.register("orders", OrderViewSet, basename="order")
urlpatterns = router.urls

6. Admin utile

@admin.register(Order)
class OrderAdmin(admin.ModelAdmin):
    list_display  = ["reference", "customer", "status", "created_at"]
    list_filter   = ["status", "created_at"]
    search_fields = ["reference", "customer__email"]
    raw_id_fields = ["customer"]     # évite le <select> avec milliers d'entrées
    actions       = ["mark_shipped"]

    @admin.action(description="Marquer comme expédié")
    def mark_shipped(self, request, queryset):
        updated = queryset.update(status=Order.Status.SHIPPED)
        self.message_user(request, f"{updated} commande(s) expédiée(s).")

7. Authentification JWT (DRF)

pip install djangorestframework-simplejwt

# settings/base.py
REST_FRAMEWORK = {
    "DEFAULT_AUTHENTICATION_CLASSES": [
        "rest_framework_simplejwt.authentication.JWTAuthentication",
    ],
    "DEFAULT_PERMISSION_CLASSES": ["rest_framework.permissions.IsAuthenticated"],
}

SIMPLE_JWT = {"ACCESS_TOKEN_LIFETIME": timedelta(minutes=15),
              "REFRESH_TOKEN_LIFETIME": timedelta(days=7)}

# urls.py racine
from rest_framework_simplejwt.views import TokenObtainPairView, TokenRefreshView
path("api/token/",         TokenObtainPairView.as_view()),
path("api/token/refresh/", TokenRefreshView.as_view()),

8. Tests

from rest_framework.test import APITestCase
from rest_framework import status

class OrderAPITest(APITestCase):
    def setUp(self):
        self.user  = UserFactory()
        self.order = OrderFactory(customer=self.user)
        self.client.force_authenticate(user=self.user)

    def test_list_returns_own_orders_only(self):
        OrderFactory()  # commande d'un autre user
        r = self.client.get("/api/orders/")
        self.assertEqual(r.status_code, status.HTTP_200_OK)
        self.assertEqual(len(r.data["results"]), 1)

pip install factory-boy pytest-django
pytest --reuse-db   # réutilise la DB entre runs pour la vitesse

9. Déploiement production

pip install gunicorn whitenoise
# settings/prod.py
STATICFILES_STORAGE = "whitenoise.storage.CompressedManifestStaticFilesStorage"

python manage.py collectstatic --no-input
gunicorn config.wsgi:application --workers 4 --bind 0.0.0.0:8000

Variables d'environnement obligatoires en prod :

SECRET_KEY=...
DATABASE_URL=postgres://user:pass@host:5432/db
DJANGO_SETTINGS_MODULE=config.settings.prod
ALLOWED_HOSTS=mondomaine.com

Garde-fous / anti-patterns

Bonnes pratiques 2026

• Django 5.x : utiliser GeneratedField pour colonnes calculées en base, LoginRequiredMiddleware au lieu de décorateurs partout.
• Tâches asynchrones : Celery + Redis ou Django Q2 pour les projets légers.
• Cache : django.core.cache + Redis ; décorer les vues coûteuses avec @cache_page.
• Observabilité : intégrer django-silk en dev pour profiler les requêtes SQL.
• Sécurité headers : django-csp + django-permissions-policy avant mise en production.
• django-storages + S3/Cloudflare R2 pour les fichiers media en production (ne jamais servir les uploads via Django en prod).