FastAPI Project Templates

Production-ready FastAPI project structures with async patterns, dependency injection, middleware, and best practices for building high-performance APIs.

When to Use This Skill

• Starting new FastAPI projects from scratch
• Implementing async REST APIs with Python
• Building high-performance web services and microservices
• Creating async applications with PostgreSQL, MongoDB
• Setting up API projects with proper structure and testing

Core Concepts

1. Project Structure

Recommended Layout:

app/
├── api/                    # API routes
│   ├── v1/
│   │   ├── endpoints/
│   │   │   ├── users.py
│   │   │   ├── auth.py
│   │   │   └── items.py
│   │   └── router.py
│   └── dependencies.py     # Shared dependencies
├── core/                   # Core configuration
│   ├── config.py
│   ├── security.py
│   └── database.py
├── models/                 # Database models
│   ├── user.py
│   └── item.py
├── schemas/                # Pydantic schemas
│   ├── user.py
│   └── item.py
├── services/               # Business logic
│   ├── user_service.py
│   └── auth_service.py
├── repositories/           # Data access
│   ├── user_repository.py
│   └── item_repository.py
└── main.py                 # Application entry

2. Dependency Injection

FastAPI's built-in DI system using Depends:

• Database session management
• Authentication/authorization
• Shared business logic
• Configuration injection

3. Async Patterns

Proper async/await usage:

• Async route handlers
• Async database operations
• Async background tasks
• Async middleware

Implementation Patterns

Pattern 1: Complete FastAPI Application

# main.py
from fastapi import FastAPI, Depends
from fastapi.middleware.cors import CORSMiddleware
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    """Application lifespan events."""
    # Startup
    await database.connect()
    yield
    # Shutdown
    await database.disconnect()

app = FastAPI(
    title="API Template",
    version="1.0.0",
    lifespan=lifespan
)

# CORS middleware
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# Include routers
from app.api.v1.router import api_router
app.include_router(api_router, prefix="/api/v1")

# core/config.py
from pydantic_settings import BaseSettings
from functools import lru_cache

class Settings(BaseSettings):
    """Application settings."""
    DATABASE_URL: str
    SECRET_KEY: str
    ACCESS_TOKEN_EXPIRE_MINUTES: int = 30
    API_V1_STR: str = "/api/v1"

    class Config:
        env_file = ".env"

@lru_cache()
def get_settings() -> Settings:
    return Settings()

# core/database.py
from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from app.core.config import get_settings

settings = get_settings()

engine = create_async_engine(
    settings.DATABASE_URL,
    echo=True,
    future=True
)

AsyncSessionLocal = sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False
)

Base = declarative_base()

async def get_db() -> AsyncSession:
    """Dependency for database session."""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()

Pattern 2: CRUD Repository Pattern

# repositories/base_repository.py
from typing import Generic, TypeVar, Type, Optional, List
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select
from pydantic import BaseModel

ModelType = TypeVar("ModelType")
CreateSchemaType = TypeVar("CreateSchemaType", bound=BaseModel)
UpdateSchemaType = TypeVar("UpdateSchemaType", bound=BaseModel)

class BaseRepository(Generic[ModelType, CreateSchemaType, UpdateSchemaType]):
    """Base repository for CRUD operations."""

    def __init__(self, model: Type[ModelType]):
        self.model = model

    async def get(self, db: AsyncSession, id: int) -> Optional[ModelType]:
        """Get by ID."""
        result = await db.execute(
            select(self.model).where(self.model.id == id)
        )
        return result.scalars().first()

    async def get_multi(
        self,
        db: AsyncSession,
        skip: int = 0,
        limit: int = 100
    ) -> List[ModelType]:
        """Get multiple records."""
        result = await db.execute(
            select(self.model).offset(skip).limit(limit)
        )
        return result.scalars().all()

    async def create(
        self,
        db: AsyncSession,
        obj_in: CreateSchemaType
    ) -> ModelType:
        """Create new record."""
        db_obj = self.model(**obj_in.dict())
        db.add(db_obj)
        await db.flush()
        await db.refresh(db_obj)
        return db_obj

    async def update(
        self,
        db: AsyncSession,
        db_obj: ModelType,
        obj_in: UpdateSchemaType
    ) -> ModelType:
        """Update record."""
        update_data = obj_in.dict(exclude_unset=True)
        for field, value in update_data.items():
            setattr(db_obj, field, value)
        await db.flush()
        await db.refresh(db_obj)
        return db_obj

    async def delete(self, db: AsyncSession, id: int) -> bool:
        """Delete record."""
        obj = await self.get(db, id)
        if obj:
            await db.delete(obj)
            return True
        return False

# repositories/user_repository.py
from app.repositories.base_repository import BaseRepository
from app.models.user import User
from app.schemas.user import UserCreate, UserUpdate

class UserRepository(BaseRepository[User, UserCreate, UserUpdate]):
    """User-specific repository."""

    async def get_by_email(self, db: AsyncSession, email: str) -> Optional[User]:
        """Get user by email."""
        result = await db.execute(
            select(User).where(User.email == email)
        )
        return result.scalars().first()

    async def is_active(self, db: AsyncSession, user_id: int) -> bool:
        """Check if user is active."""
        user = await self.get(db, user_id)
        return user.is_active if user else False

user_repository = UserRepository(User)

Pattern 3: Service Layer

# services/user_service.py
from typing import Optional
from sqlalchemy.ext.asyncio import AsyncSession
from app.repositories.user_repository import user_repository
from app.schemas.user import UserCreate, UserUpdate, User
from app.core.security import get_password_hash, verify_password

class UserService:
    """Business logic for users."""

    def __init__(self):
        self.repository = user_repository

    async def create_user(
        self,
        db: AsyncSession,
        user_in: UserCreate
    ) -> User:
        """Create new user with hashed password."""
        # Check if email exists
        existing = await self.repository.get_by_email(db, user_in.email)
        if existing:
            raise ValueError("Email already registered")

        # Hash password
        user_in_dict = user_in.dict()
        user_in_dict["hashed_password"] = get_password_hash(user_in_dict.pop("password"))

        # Create user
        user = await self.repository.create(db, UserCreate(**user_in_dict))
        return user

    async def authenticate(
        self,
        db: AsyncSession,
        email: str,
        password: str
    ) -> Optional[User]:
        """Authenticate user."""
        user = await self.repository.get_by_email(db, email)
        if not user:
            return None
        if not verify_password(password, user.hashed_password):
            return None
        return user

    async def update_user(
        self,
        db: AsyncSession,
        user_id: