Routers for Separation

APIRouter groups related endpoints into modules (users, orders, admin), each with its own prefix, tags, dependencies and responses, then app.include_router() mounts them. A common layout: one package per feature containing router.py, schemas.py, models.py and service.py, keeping HTTP concerns in routers and business logic in services.

# app/orders/router.py
from fastapi import APIRouter, Depends

router = APIRouter(prefix="/orders", tags=["orders"], dependencies=[Depends(require_user)])


@router.get("")
async def list_orders(db: DB, user: CurrentUser) -> list[OrderOut]:
    return await service.list_for_user(db, user.id)


@router.post("", status_code=201)
async def create_order(body: OrderCreate, db: DB, user: CurrentUser) -> OrderOut:
    return await service.create(db, user.id, body)


# app/main.py
from app.orders.router import router as orders_router
from app.admin.router import router as admin_router

app = FastAPI(lifespan=lifespan)
app.include_router(orders_router, prefix="/api/v1")
app.include_router(admin_router, prefix="/api/v1", dependencies=[Depends(require_admin)])

Common pitfalls

• One giant main.py with every endpoint.
• Business logic inside route functions, making it hard to reuse from jobs or tests.
• Circular imports between feature modules.

Key points

• One router per feature
• Prefixes, tags and dependencies per router
• Keep logic in services

Further reading: FastAPI: Bigger applications