django-patterns

Django開発パターン

スケーラブルで保守性の高いアプリケーションのための、プロダクション品質のDjangoアーキテクチャパターン。

使用タイミング

• Django Webアプリケーションの構築
• Django REST Framework APIの設計
• Django ORMとモデルの操作
• Djangoプロジェクト構造のセットアップ
• キャッシュ、シグナル、ミドルウェアの実装

プロジェクト構造

推奨レイアウト

myproject/
├── config/
│   ├── __init__.py
│   ├── settings/
│   │   ├── __init__.py
│   │   ├── base.py          # 基本設定
│   │   ├── development.py   # 開発設定
│   │   ├── production.py    # 本番設定
│   │   └── test.py          # テスト設定
│   ├── 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/
        └── ...

設定分割パターン

# 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',
    # ローカルアプリ
    '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

# ロギング
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,
        },
    },
}

モデル設計パターン

モデルのベストプラクティス

from django.db import models
from django.contrib.auth.models import AbstractUser
from django.core.validators import MinValueValidator, MaxValueValidator

class User(AbstractUser):
    """AbstractUserを拡張したカスタムユーザーモデル。"""
    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 = 'ユーザー'
        verbose_name_plural = 'ユーザー'
        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):
    """適切なフィールド設定を持つ製品モデル。"""
    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のベストプラクティス

from django.db import models

class ProductQuerySet(models.QuerySet):
    """Productモデル用のカスタムQuerySet。"""

    def active(self):
        """有効な製品のみを返す。"""
        return self.filter(is_active=True)

    def with_category(self):
        """N+1クエリを避けるために関連カテゴリを選択。"""
        return self.select_related('category')

    def with_tags(self):
        """多対多リレーションのためにタグを先読み。"""
        return self.prefetch_related('tags')

    def in_stock(self):
        """在庫のある製品を返す。"""
        return self.filter(stock__gt=0)

    def search(self, query):
        """名前または説明で製品を検索。"""
        return self.filter(
            models.Q(name__icontains=query) |
            models.Q(description__icontains=query)
        )

class Product(models.Model):
    # ... フィールド ...

    objects = ProductQuerySet.as_manager()  # カスタムQuerySetを使用

# 使用例
Product.objects.active().with_category().in_stock()

マネージャーメソッド

class ProductManager(models.Manager):
    """複雑なクエリのためのカスタムマネージャー。"""

    def get_or_none(self, **kwargs):
        """DoesNotExistの代わりにオブジェクトまたはNoneを返す。"""
        try:
            return self.get(**kwargs)
        except self.model.DoesNotExist:
            return None

    def create_with_tags(self, name, price, tag_names):
        """関連タグとともに製品を作成。"""
        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):
        """複数製品の在庫を一括更新。"""
        return self.filter(id__in=product_ids).update(stock=quantity)

# モデル内で
class Product(models.Model):
    # ... フィールド ...
    custom = ProductManager()

Django REST Framework パターン

シリアライザーパターン

from rest_framework import serializers
from django.contrib.auth.password_validation import validate_password
from .models import Product, User

class ProductSerializer(serializers.ModelSerializer):
    """Productモデル用のシリアライザー。"""

    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):
        """該当する場合、割引価格を計算。"""
        if hasattr(obj, 'discount') and obj.discount:
            return obj.price * (1 - obj.discount.percent / 100)
        return obj.price

    def validate_price(self, value):
        """価格が非負であることを確認。"""
        if value < 0:
            raise serializers.ValidationError("価格は負の値にできません。")
        return value

class ProductCreateSerializer(serializers.ModelSerializer):
    """製品作成用のシリアライザー。"""

    class Meta:
        model = Product
        fields = ['name', 'description', 'price', 'stock', 'category']

    def validate(self, data):
        """複数フィールドのカスタムバリデーション。"""
        if data['price'] > 10000 and data['stock'] > 100:
            raise serializers.ValidationError(
                "高額商品を大量に在庫することはできません。"
            )
        return data

class UserRegistrationSerializer(serializers.ModelSerializer):
    """ユーザー登録用のシリアライザー。"""

    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):
        """パスワードが一致することを確認。"""
        if data['password'] != data['password_confirm']:
            raise serializers.ValidationError({
                "password_confirm": "パスワードフィールドが一致しません。"
            })
        return data

    def create(self, validated_data):
        """ハッシュ化されたパスワードでユーザーを作成。"""
        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パターン

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):
    """Productモデル用のViewSet。"""

    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):
        """アクションに応じて適切なシリアライザーを返す。"""
        if self.action == 'create':
            return ProductCreateSerializer
        return ProductSerializer

    def perform_create(self, serializer):
        """ユーザーコンテキストを保持して保存。"""
        serializer.save(created_by=self.request.user)

    @action(detail=False, methods=['get'])
    def featured(self, request):
        """おすすめ製品を返す。"""
        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):
        """製品を購入する。"""
        product = self.get_object()
        service = ProductService()
        result = service.purchase(product, request.user)
        return Response(result, status=status.HTTP_201_CREATED)

    @action(detail=False, methods=['get'], permission_classes=[IsAuthenticated])
    def my_products(self, request):
        """現在のユーザーが作成した製品を返す。"""
        products = self.queryset.filter(created_by=request.user)
        page = self.paginate_queryset(products)
        serializer = self.get_serializer(page, many=True)
        return self.get_paginated_response(serializer.data)

カスタムアクション

from rest_framework.decorators import api_view, permission_classes
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response

@api_view(['POST'])
@permission_classes([IsAuthenticated])
def add_to_cart(request):
    """製品をユーザーカートに追加。"""
    product_id = request.data.get('product_id')
    quantity = request.data.get('quantity', 1)

    try:
        product = Product.objects.get(id=product_id)
    except Product.DoesNotExist:
        return Response(
            {'error': '製品が見つかりません'},
            status=status.HTTP_404_NOT_FOUND
        )

    cart, _ = Cart.objects.get_or_create(user=request.user)
    CartItem.objects.create(
        cart=cart,
        product=product,
        quantity=quantity
    )

    return Response({'message': 'カートに追加しました'}, status=status.HTTP_201_CREATED)

サービスレイヤーパターン

# apps/orders/services.py
from typing import Optional
from django.db import transaction
from .models import Order, OrderItem

class OrderService:
    """注文関連のビジネスロジックのためのサービスレイヤー。"""

    @staticmethod
    @transaction.atomic

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