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 entry2. 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: int,
user_in: UserUpdate
) -> Optional[User]:
"""Update user."""
user = await self.repository.get(db, user_id)
if not user:
return None
if user_in.password:
user_in_dict = user_in.dict(exclude_unset=True)
user_in_dict["hashed_password"] = get_password_hash(
user_in_dict.pop("password")
)
user_in = UserUpdate(**user_in_dict)
return await self.repository.update(db, user, user_in)
user_service = UserService()Pattern 4: API Endpoints with Dependencies
# api/v1/endpoints/users.py
from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.ext.asyncio import AsyncSession
from typing import List
from app.core.database import get_db
from app.schemas.user import User, UserCreate, UserUpdate
from app.services.user_service import user_service
from app.api.dependencies import get_current_user
router = APIRouter()
@router.post("/", response_model=User, status_code=status.HTTP_201_CREATED)
async def create_user(
user_in: UserCreate,
db: AsyncSession = Depends(get_db)
):
"""Create new user."""
try:
user = await user_service.create_user(db, user_in)
return user
except ValueError as e:
raise HTTPException(status_code=400, detail=str(e))
@router.get("/me", response_model=User)
async def read_current_user(
current_user: User = Depends(get_current_user)
):
"""Get current user."""
return current_user
@router.get("/{user_id}", response_model=User)
async def read_user(
user_id: int,
db: AsyncSession = Depends(get_db),
current_user: User = Depends(get_current_user)
):
"""Get user by ID."""
user = await user_service.repository.get(db, user_id)
if not user:
raise HTTPException(status_code=404, detail="User not found")
return user
@router.patch("/{user_id}", response_model=User)
async def update_user(
user_id: int,
user_in: UserUpdate,
db: AsyncSession = Depends(get_db),
current_user: User = Depends(get_current_user)
):
"""Update user."""
if current_user.id != user_id:
raise HTTPException(status_code=403, detail="Not authorized")
user = await user_service.update_user(db, user_id, user_in)
if not user:
raise HTTPException(status_code=404, detail="User not found")
return user
@router.delete("/{user_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_user(
user_id: int,
db: AsyncSession = Depends(get_db),
current_user: User = Depends(get_current_user)
):
"""Delete user."""
if current_user.id != user_id:
raise HTTPException(status_code=403, detail="Not authorized")
deleted = await user_service.repository.delete(db, user_id)
if not deleted:
raise HTTPException(status_code=404, detail="User not found")Pattern 5: Authentication & Authorization
# core/security.py
from datetime import datetime, timedelta
from typing import Optional
from jose import JWTError, jwt
from passlib.context import CryptContext
from app.core.config import get_settings
settings = get_settings()
pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
ALGORITHM = "HS256"
def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
"""Create JWT access token."""
to_encode = data.copy()
if expires_delta:
expire = datetime.utcnow() + expires_delta
else:
expire = datetime.utcnow() + timedelta(minutes=15)
to_encode.update({"exp": expire})
encoded_jwt = jwt.encode(to_encode, settings.SECRET_KEY, algorithm=ALGORITHM)
return encoded_jwt
def verify_password(plain_password: str, hashed_password: str) -> bool:
"""Verify password against hash."""
return pwd_context.verify(plain_password, hashed_password)
def get_password_hash(password: str) -> str:
"""Hash password."""
return pwd_context.hash(password)
# api/dependencies.py
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from sqlalchemy.ext.asyncio import AsyncSession
from app.core.database import get_db
from app.core.security import ALGORITHM
from app.core.config import get_settings
from app.repositories.user_repository import user_repository
oauth2_scheme = OAuth2PasswordBearer(tokenUrl=f"{settings.API_V1_STR}/auth/login")
async def get_current_user(
db: AsyncSession = Depends(get_db),
token: str = Depends(oauth2_scheme)
):
"""Get current authenticated user."""
credentials_exception = HTTPException(
status_code=status.HTTP_401_UNAUTHORIZED,
detail="Could not validate credentials",
headers={"WWW-Authenticate": "Bearer"},
)
try:
payload = jwt.decode(token, settings.SECRET_KEY, algorithms=[ALGORITHM])
user_id: int = payload.get("sub")
if user_id is None:
raise credentials_exception
except JWTError:
raise credentials_exception
user = await user_repository.get(db, user_id)
if user is None:
raise credentials_exception
return userTesting
# tests/conftest.py
import pytest
import asyncio
from httpx import AsyncClient
from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from sqlalchemy.orm import sessionmaker
from app.main import app
from app.core.database import get_db, Base
TEST_DATABASE_URL = "sqlite+aiosqlite:///:memory:"
@pytest.fixture(scope="session")
def event_loop():
loop = asyncio.get_event_loop_policy().new_event_loop()
yield loop
loop.close()
@pytest.fixture
async def db_session():
engine = create_async_engine(TEST_DATABASE_URL, echo=True)
async with engine.begin() as conn:
await conn.run_sync(Base.metadata.create_all)
AsyncSessionLocal = sessionmaker(
engine, class_=AsyncSession, expire_on_commit=False
)
async with AsyncSessionLocal() as session:
yield session
@pytest.fixture
async def client(db_session):
async def override_get_db():
yield db_session
app.dependency_overrides[get_db] = override_get_db
async with AsyncClient(app=app, base_url="http://test") as client:
yield client
# tests/test_users.py
import pytest
@pytest.mark.asyncio
async def test_create_user(client):
response = await client.post(
"/api/v1/users/",
json={
"email": "test@example.com",
"password": "testpass123",
"name": "Test User"
}
)
assert response.status_code == 201
data = response.json()
assert data["email"] == "test@example.com"
assert "id" in data