Fastapi Templates

# 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

```python
# 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

```python
# repositories/base_repository.py
from typing import Generic, TypeVar, Type, Optional, List
from sqlalchemy.ext.asyncio