Backend Boilerplates python Intermediate

FastAPI Dependency Injection Chain

Compose multiple FastAPI dependencies — DB session, auth user, and feature flag check.

python

from fastapi import Depends, HTTPException

async def get_db(): ...  # yields session

async def current_user(token: str = Depends(oauth2_scheme), db = Depends(get_db)) -> User:
    user = verify_token(token, db)
    if not user:
        raise HTTPException(401, "Unauthorized")
    return user

async def premium_user(user: User = Depends(current_user)) -> User:
    if user.plan != "premium":
        raise HTTPException(403, "Premium plan required")
    return user

@app.get("/export", dependencies=[Depends(premium_user)])
async def export(): ...