Using lifespan event on APIRoute() instead in FastAPI()

[Ammar-Azman]

Privileged issue

• I'm @tiangolo or he asked me directly to create an issue here.

Issue Content

I have asked Mr @tiangolo on Twitter this question and he suggested me to ask in Github so it can benefit others and I am agree with him.

I have tried to apply lifespan event on APIrouter() instead of app object, based on the FastAPI tutorial. But it seems that to showed the Keyword error on "answer_to_everything". I have search on Google but I don't found any discussion related to this.

I found that APIRoute() class has lifespan parameter too (same as FastAPI()), but might be require certain or additional configuration to make it happened. Any way that we can apply the lifespan on router?

I hope anyone can help to solve this issue. Thank you for creating an awesome API framework.

[Kludex]

I have asked Mr @tiangolo on Twitter this question and he suggested me to ask in Github so it can benefit others and I am agree with him.

He probably meant to create a discussion, not an issue.

I found that APIRoute() class has lifespan parameter too (same as FastAPI()), but might be require certain or additional configuration to make it happened. Any way that we can apply the lifespan on route?

The APIRouter is the one that accepts lifespan, not APIRoute.

Any way that we can apply the lifespan on route?

For the moment, is not possible.

[Ammar-Azman]

Alright thanks @Kludex for the answer.

[stur86]

Adding it to APIRouter doesn't work either for me, though. Only FastAPI seems to properly execute the lifespan context methods. Is something missing?

[noirbizarre]

Hi 👋🏼

I was going to submit an issue, but I saw this discussion.
Currently on_startup and on_shutdown are deprecated in favor of lifespan on both FastAPI and APIRouter while lifespan are only supported on FastAPI.

Here is a quick gist showing APIRouter does not support lifespan: https://gist.github.com/noirbizarre/a6028f561adb5949c7f21471b9b02032

What is FastAPI official position on this ?

1. APIRouter-level events are not supported anymore
2. APIRouter-level lifespan support is missing and this is an issue that need a fix
3. APIRouter-level events are not deprecated and the warning is app warning is leaking on APIRouter and this need a fix

[naimetti]

Same here

[joshwilson-dbx]

@Kludex I might be misreading your answer, but it looks like this discussion was resolved by you just clearing up some confusion about the difference between APIRoute and APIRouter. From my reading it looks like you're saying the intent is for APIRouter to fully support the lifespan functionality.

I can also confirm that a lifespan asynccontextmanager function is not invoked when provided to a sub-APIRouter. Is this intentional?

The FastAPI docs do mention that this is not supported for sub-applications, but perhaps that should be updated to include sub-routers, too. At least for the time being. For now, I think we'll have to fall back to the deprecated lifecycle events pattern or something like this:

def startup():
    logger.info("Starting sub router")


router = APIRouter(on_startup=[startup])

app = FastAPI()
app.include_router(router, '/myprefix')

Looking into the code, I don't see FastAPI doing anything with the app's lifespan argument other than handing it to its internal APIRouter instance. I think we could support the sub-router case (and perhaps the sub-application case). To my uneducated eyes, it seems like it would be a relatively easy thing to have the FastAPI app wrap it's own lifespan manager around any user-provided one and which would invoke any sub-routers' lifespan managers before invoking the user-provided app-level one (or maybe the user-provided app one is invoked first?). Would a PR be welcome?

[noirbizarre]

I think the fact that:

• the APIRouter documentation itself is saying explicitely that on_startup and on_shutdown are deprecated in favor or lifespans
• DeprecationWarnings are raised when you use on_startup and on_shutdown
• the lifespan parameter is silently ignored

are misleading and either:

• it should be fixed (I can try to submit a fix if a PR is welcome) if lifespan is expected to work on APIRouter
• documentation should be fixed and DeprecationWarning removed on APIRouter on_startup and on_shutdown parameters if support for lifespan is not intended

[nicocti]

True. Actually, a PR is already opened here : #9630 but it seems that it should be fixed upward (in Starlette). Unfortunately, Starlette won't implement before 1.0 (if I got it right here: encode/starlette#1988 (comment)). I'd also benefit from using lifespan on routers on my side.

[kamalkraj]

Hi 👋🏼

I was going to submit an issue, but I saw this discussion. Currently on_startup and on_shutdown are deprecated in favor of lifespan on both FastAPI and APIRouter while lifespan are only supported on FastAPI.

Here is a quick gist showing APIRouter does not support lifespan: https://gist.github.com/noirbizarre/a6028f561adb5949c7f21471b9b02032

What is FastAPI official position on this ?

1. APIRouter-level events are not supported anymore
2. APIRouter-level lifespan support is missing and this is an issue that need a fix
3. APIRouter-level events are not deprecated and the warning is app warning is leaking on APIRouter and this need a fix

from contextlib import asynccontextmanager

from fastapi import APIRouter, FastAPI, Request


@asynccontextmanager
async def lifespan(app: FastAPI):
    # Load the ML model
    app.ml_model = lambda x: x * 42
    yield
    # Clean up the ML models and release the resources
    del app.ml_model


app = FastAPI(lifespan=lifespan)
router = APIRouter()


@router.get("/predict")
async def predict(request: Request, x: float):
    result = request.app.ml_model(x)
    return {"result": result}


app.include_router(router)