FastAPI Tutorial 2026: Build a REST API with PostgreSQL, Auth, and Async

Why FastAPI?

FastAPI is now the most popular Python web framework for APIs, surpassing Flask in developer surveys. Key advantages:

• Automatic docs: Swagger UI generated from your code
• Type safety: Pydantic validation on all inputs and outputs
• Async: native async/await support
• Fast: performance comparable to Node.js

Installation

pip install fastapi uvicorn[standard] sqlalchemy asyncpg pydantic-settings python-jose passlib

First Endpoint

# main.py
from fastapi import FastAPI

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

@app.get("/")
async def root():
    return {"message": "Hello, World!"}

@app.get("/items/{item_id}")
async def get_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "query": q}

uvicorn main:app --reload
# Visit http://localhost:8000/docs for auto-generated Swagger UI

Pydantic Models for Request/Response

from pydantic import BaseModel, EmailStr
from datetime import datetime

class UserCreate(BaseModel):
    username: str
    email: EmailStr
    password: str

class UserResponse(BaseModel):
    id: int
    username: str
    email: str
    created_at: datetime

    model_config = {"from_attributes": True}  # allow ORM models

@app.post("/users/", response_model=UserResponse, status_code=201)
async def create_user(user: UserCreate):
    # FastAPI validates input automatically
    # Returns 422 if validation fails
    ...

Database with SQLAlchemy Async

from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from sqlalchemy.orm import DeclarativeBase, mapped_column, Mapped
from sqlalchemy import String, DateTime, func
from typing import AsyncGenerator

DATABASE_URL = "postgresql+asyncpg://user:password@localhost/mydb"
engine = create_async_engine(DATABASE_URL)

class Base(DeclarativeBase):
    pass

class User(Base):
    __tablename__ = "users"

    id: Mapped[int] = mapped_column(primary_key=True)
    username: Mapped[str] = mapped_column(String(50), unique=True)
    email: Mapped[str] = mapped_column(String(200), unique=True)
    hashed_password: Mapped[str] = mapped_column(String(200))
    created_at: Mapped[datetime] = mapped_column(server_default=func.now())

async def get_db() -> AsyncGenerator[AsyncSession, None]:
    async with AsyncSession(engine) as session:
        yield session

Dependency Injection

from fastapi import Depends
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select

async def get_user_by_id(
    user_id: int,
    db: AsyncSession = Depends(get_db)
) -> User:
    result = await db.execute(select(User).where(User.id == user_id))
    user = result.scalar_one_or_none()
    if not user:
        raise HTTPException(status_code=404, detail="User not found")
    return user

@app.get("/users/{user_id}", response_model=UserResponse)
async def get_user(user: User = Depends(get_user_by_id)):
    return user

JWT Authentication

from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from jose import JWTError, jwt
from passlib.context import CryptContext

SECRET_KEY = "your-secret-key"
ALGORITHM = "HS256"
pwd_context = CryptContext(schemes=["bcrypt"])
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def create_token(user_id: int) -> str:
    return jwt.encode({"sub": str(user_id)}, SECRET_KEY, algorithm=ALGORITHM)

async def get_current_user(
    token: str = Depends(oauth2_scheme),
    db: AsyncSession = Depends(get_db)
) -> User:
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        user_id = int(payload["sub"])
    except JWTError:
        raise HTTPException(status_code=401, detail="Invalid token")
    return await get_user_by_id(user_id, db)

@app.post("/token")
async def login(form: OAuth2PasswordRequestForm = Depends(), db: AsyncSession = Depends(get_db)):
    # Verify credentials and return token
    ...

@app.get("/me", response_model=UserResponse)
async def get_me(current_user: User = Depends(get_current_user)):
    return current_user

Background Tasks

from fastapi import BackgroundTasks
import smtplib

def send_welcome_email(email: str):
    # runs after the response is sent
    print(f"Sending welcome email to {email}")

@app.post("/users/", response_model=UserResponse, status_code=201)
async def create_user(user: UserCreate, background_tasks: BackgroundTasks, db: AsyncSession = Depends(get_db)):
    # Create user in DB
    db_user = User(username=user.username, email=user.email)
    db.add(db_user)
    await db.commit()

    # Schedule email without blocking response
    background_tasks.add_task(send_welcome_email, user.email)
    return db_user

Deploy with Uvicorn and nginx

# Production: multiple workers
uvicorn main:app --host 0.0.0.0 --port 8000 --workers 4

server {
    listen 80;
    server_name api.yourdomain.com;

    location / {
        proxy_pass http://127.0.0.1:8000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}