fastapi

FastAPI REST API Skill

Step 1: Setup

pip install fastapi uvicorn[standard] pydantic[email] pydantic-settings

Project Structure

app/
├── main.py              # App instance, lifespan, router includes
├── config.py            # Settings via pydantic-settings
├── dependencies.py      # Shared dependencies (DB session, auth)
├── routers/
│   ├── users.py
│   └── posts.py
├── models/
│   ├── user.py          # SQLAlchemy models
│   └── post.py
├── schemas/
│   ├── user.py          # Pydantic request/response schemas
│   └── post.py
└── services/
    ├── auth.py          # Auth business logic
    └── users.py         # User business logic

---

Step 2: Application Setup with Lifespan

# app/main.py
from contextlib import asynccontextmanager
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from .database import engine
from .models import Base
from .routers import users, posts

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Startup: create tables
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    yield
    # Shutdown: close connections
    await engine.dispose()

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

app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://myapp.com"],  # or ["*"] for dev
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

app.include_router(users.router, prefix="/users", tags=["users"])
app.include_router(posts.router, prefix="/posts", tags=["posts"])

@app.get("/health")
async def health_check():
    return {"status": "ok"}

---

Step 3: Pydantic Schemas (Request / Response)

# app/schemas/user.py
from pydantic import BaseModel, EmailStr, Field, ConfigDict
from datetime import datetime
from uuid import UUID

class UserCreate(BaseModel):
    name: str = Field(min_length=2, max_length=100)
    email: EmailStr
    password: str = Field(min_length=8)

class UserUpdate(BaseModel):
    name: str | None = Field(None, min_length=2, max_length=100)
    email: EmailStr | None = None

class UserResponse(BaseModel):
    model_config = ConfigDict(from_attributes=True)  # ORM mode

    id: UUID
    name: str
    email: str
    created_at: datetime
    # Never include password in response