asgi_fastapi.py

"""
Example demonstrating use with the FastAPI web framework.

Requires the "postgresql" service to be running.
To install prerequisites: pip install sqlalchemy asycnpg fastapi uvicorn
To run: uvicorn asgi_fastapi:app

It should print a line on the console on a one-second interval while running a
basic web app at http://localhost:8000.
"""

from __future__ import annotations

from datetime import datetime

from fastapi import FastAPI
from fastapi.middleware import Middleware
from fastapi.requests import Request
from fastapi.responses import PlainTextResponse, Response
from sqlalchemy.ext.asyncio import create_async_engine
from starlette.types import ASGIApp, Receive, Scope, Send

from apscheduler import AsyncScheduler
from apscheduler.datastores.sqlalchemy import SQLAlchemyDataStore
from apscheduler.eventbrokers.asyncpg import AsyncpgEventBroker
from apscheduler.triggers.interval import IntervalTrigger


def tick():
    print("Hello, the time is", datetime.now())


class SchedulerMiddleware:
    def __init__(
        self,
        app: ASGIApp,
        scheduler: AsyncScheduler,
    ) -> None:
        self.app = app
        self.scheduler = scheduler

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] == "lifespan":
            async with self.scheduler:
                await self.scheduler.add_schedule(
                    tick, IntervalTrigger(seconds=1), id="tick"
                )
                await self.scheduler.start_in_background()
                await self.app(scope, receive, send)
        else:
            await self.app(scope, receive, send)


async def root(request: Request) -> Response:
    return PlainTextResponse("Hello, world!")


engine = create_async_engine("postgresql+asyncpg://postgres:secret@localhost/testdb")
data_store = SQLAlchemyDataStore(engine)
event_broker = AsyncpgEventBroker.from_async_sqla_engine(engine)
scheduler = AsyncScheduler(data_store, event_broker)
middleware = [Middleware(SchedulerMiddleware, scheduler=scheduler)]
app = FastAPI(middleware=middleware)
app.add_api_route("/", root)