python - Future task attached to a different loop

Question

I am trying to connect to mongodb in FastAPI. I am repeatedly getting this exception.

File - main.py

app = FastAPI(
    title=config.PROJECT_NAME, docs_url="/api/docs", openapi_url="/api"
)

@app.get("/api/testing")
async def testit():
    user_collection = readernetwork_db.get_collection("user_collection")
    all_users = await user_collection.find_one({"email": "sample_email"})
    print("all users --- ", all_users)
    return all_users

if __name__ == "__main__":
    uvicorn.run("main:app", host="0.0.0.0", reload=True, port=8888)

File - session.py

import motor.motor_asyncio
from app.core import config


print("here we go again....")
client = motor.motor_asyncio.AsyncIOMotorClient(
    config.MONGOATLAS_DATABASE_URI)
readernetwork_db = client.get_database("readernetwork")

Exception -:

all_users = await user_collection.find_one({"email": "sample_email"})

RuntimeError: Task <Task pending name='Task-4' coro=<RequestResponseCycle.run_asgi() running at /usr/local/lib/python3.8/site-packages/uvicorn/protocols/http/h11_impl.py:389> cb=[set.discard()]> got Future <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /usr/local/lib/python3.8/asyncio/futures.py:360]> attached to a different loop

I don't know where I am getting this wrong. Should I specify a event loop to motor?

question from:https://stackoverflow.com/questions/65542103/future-task-attached-to-a-different-loop

Answer 1

You can have mongodb motor client in the global scope, but creating and closing it should be done inside an async function. The most preferable way of doing that in startup and shutdown handler of the application. Like so:

# mongodb.py
from motor.motor_asyncio import AsyncIOMotorClient


db_client: AsyncIOMotorClient = None


async def get_db_client() -> AsyncIOMotorClient:
    """Return database client instance."""
    return db_client


async def connect_db():
    """Create database connection."""
    db_client = AsyncIOMotorClient(DB_URL)

async def close_mongo_connection():
    """Close database connection."""
    db_client.close()

# main.py
app = FastAPI(title=PROJECT_NAME)
...
app.add_event_handler("startup", connect_db)
app.add_event_handler("shutdown", close_db)