fastapi-templates

name	fastapi-templates
description	Create production-ready FastAPI projects with async patterns, dependency injection, and comprehensive error handling. Use when building new FastAPI applications or setting up backend API projects.

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 :
        env_file = 


 () -> Settings:
     Settings()


 sqlalchemy.ext.asyncio  create_async_engine, AsyncSession
 sqlalchemy.ext.declarative  declarative_base
 sqlalchemy.orm  sessionmaker
 app.core.config  get_settings

settings = get_settings()

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

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

Base = declarative_base()

  () -> AsyncGenerator[, ]:
    
      AsyncSessionLocal()  session:
        :
             session
             session.commit()
         Exception:
             session.rollback()
            
        :
             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
    ) -> [ModelType]:
        
        result =  db.execute(
            select(.model).offset(skip).limit(limit)
        )
         result.scalars().()

      () -> ModelType:
        
        db_obj = .model(**obj_in.())
        db.add(db_obj)
         db.flush()
         db.refresh(db_obj)
         db_obj

      () -> ModelType:
        
        update_data = obj_in.(exclude_unset=)
         field, value  update_data.items():
            (db_obj, field, value)
         db.flush()
         db.refresh(db_obj)
         db_obj

      () -> :
        
        obj =  .get(db, )
         obj:
             db.delete(obj)
             
         


 app.repositories.base_repository  BaseRepository
 app.models.user  User
 app.schemas.user  UserCreate, UserUpdate

 (BaseRepository[User, UserCreate, UserUpdate]):
    

      () -> [User]:
        
        result =  db.execute(
            select(User).where(User.email == email)
        )
         result.scalars().first()

      () -> :
        
        user =  .get(db, user_id)
         user.is_active  user  

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: ,
        password: 
    ) -> [User]:
        
        user =  .repository.get_by_email(db, email)
          user:
             
          verify_password(password, user.hashed_password):
             
         user

      () -> [User]:
        
        user =  .repository.get(db, user_id)
          user:
             

         user_in.password:
            user_in_dict = user_in.(exclude_unset=)
            user_in_dict[] = get_password_hash(
                user_in_dict.pop()
            )
            user_in = UserUpdate(**user_in_dict)

          .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)
  ():
    
    user =  user_service.repository.get(db, user_id)
      user:
         HTTPException(status_code=, detail=)
     user


  ():
    
     current_user. != user_id:
         HTTPException(status_code=, detail=)

    user =  user_service.update_user(db, user_id, user_in)
      user:
         HTTPException(status_code=, detail=)
     user


  ():
    
     current_user. != user_id:
         HTTPException(status_code=, detail=)

    deleted =  user_service.repository.delete(db, user_id)
      deleted:
         HTTPException(status_code=, detail=)

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
 fastapi  Depends, HTTPException, status
 fastapi.security  OAuth2PasswordBearer
 jose  JWTError, jwt
 sqlalchemy.ext.asyncio  AsyncSession

 app.core.database  get_db
 app.core.security  ALGORITHM
 app.core.config  get_settings
 app.repositories.user_repository  user_repository

oauth2_scheme = OAuth2PasswordBearer(tokenUrl=)

  ():
    
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail=,
        headers={: },
    )

    :
        payload = jwt.decode(token, settings.SECRET_KEY, algorithms=[ALGORITHM])
        user_id:  = payload.get()
         user_id  :
             credentials_exception
     JWTError:
         credentials_exception

    user =  user_repository.get(db, user_id)
     user  :
         credentials_exception

     user

Testing

# 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=)  client:
         client


 pytest


  ():
    response =  client.post(
        ,
        json={
            : ,
            : ,
            : 
        }
    )
     response.status_code == 
    data = response.json()
     data[] == 
       data

Resources

• references/fastapi-architecture.md: Detailed architecture guide
• references/async-best-practices.md: Async/await patterns
• references/testing-strategies.md: Comprehensive testing guide
• assets/project-template/: Complete FastAPI project
• assets/docker-compose.yml: Development environment setup

Best Practices

1. Async All The Way: Use async for database, external APIs
2. Dependency Injection: Leverage FastAPI's DI system
3. Repository Pattern: Separate data access from business logic
4. Service Layer: Keep business logic out of routes
5. Pydantic Schemas: Strong typing for request/response
6. Error Handling: Consistent error responses
7. Testing: Test all layers independently

Common Pitfalls

• Blocking Code in Async: Using synchronous database drivers
• No Service Layer: Business logic in route handlers
• Missing Type Hints: Loses FastAPI's benefits
• Ignoring Sessions: Not properly managing database sessions
• No Testing: Skipping integration tests
• Tight Coupling: Direct database access in routes
• Overly Large Functions: Avoid functions that do too much; break into smaller, focused functions.