fastapi-dev

name	fastapi-dev
description	Guidelines and architecture patterns for FastAPI backend development, focusing on dependency injection, type safety, and clean routers.

FastAPI Backend Guide

Follow this guide to build robust, framework-agnostic, and performant APIs.

Routing and Layer Separation

• Routers: Keep router code thin. Only validate request bodies/parameters and serialize responses. Delegate all business logic to service functions.
• Services: Write business logic in services that are database and framework-agnostic.
• Models: Use SQLAlchemy 2.0 async mapping for ORM models.
• Schemas: Always use Pydantic v2 schemas for request validation and response serialization. Never return raw database models directly.

Async Operations

• Use async router endpoints (async def).
• Perform database interactions asynchronously using SQLAlchemy's AsyncSession.
• Avoid mixing synchronous and asynchronous blocking calls (e.g. use non-blocking HTTP clients like httpx instead of requests).

Dependency Injection

• Inject the database session and authentication details using FastAPI's dependency injection system (Depends).
• Example:

from fastapi import APIRouter, Depends
from sqlalchemy.ext.asyncio import AsyncSession
from src.database import get_db

router = APIRouter()

@router.get("/items/{item_id}", response_model=ItemResponse)
async def read_item(item_id: int, db: AsyncSession = Depends(get_db)):
    return await ItemService.get_item(db, item_id)