init_app doesn't seem to work with lifespans

[ChrsPi]

Versions: fastapi: 0.103.2, fastapi-mqtt: 2.0.0

When I use a fastapi lifespan (e.g. in order to setup a db connection) the init_app method does not seem to work anymore. The client will not connect. I guess because the now deprecated startup and shutdown events won't get triggered when using lifespans.

Lifespan documentation: https://fastapi.tiangolo.com/advanced/events/

The init_app method for reference:

def init_app(self, app: FastAPI) -> None:  # pragma: no cover
    @app.on_event("startup")
    async def startup():
        await self.connection()

    @app.on_event("shutdown")
    async def shutdown():
        await self.client.disconnect()

Calling the connection() and disconnect() methods themselves from the lifespan then works again:

...
mqtt_config = MQTTConfig(host=settings.mqtt_host, port=settings.mqtt_port)
mqtt = FastMQTT(config=mqtt_config)

@asynccontextmanager
async def lifespan(_: FastAPI) -> AsyncGenerator[None, None]:
    """Run tasks before and after the server starts.

    Specifically, we initialize the database models before the server starts
    to ensure that the database has the correct schema.
    """
    try:
        init_models()
        await mqtt.connection()

    except ConnectionRefusedError as exc:
        raise ConnectionRefusedError("Failed to connect to the database") from exc
    yield
    await mqtt.client.disconnect()

Is it an error on my part with using the lifespan? Otherwise adding a hint for this to the official documentation will help others.

[azogue]

When I use a fastapi lifespan (e.g. in order to setup a db connection) the init_app method does not seem to work anymore.

Is it an error on my part with using the lifespan?

Hi @ChrsPi, it's normal. When using a lifespan method to setup, yield, and shutdown the app, that init_app method is not called anymore, and the connection and disconnection has to be called the way you do in the snippet 👍

Take into account that disconnections and re-connections to the MQTT broker are also not managed by default, but you can define callbacks with @mqtt.on_connect() and @mqtt.on_disconnect() decorators to manage those events

Otherwise adding a hint for this to the official documentation will help others.

For sure! PRs to improve docs are always welcome 🙏

[ChrsPi]

Thanks a lot for your response and explanation!