Need suggestions to work with motor (MongoDB async driver)

[hieu-n]

My app structure (simplified):

app/
   templates/
   __init__.py
manage.py

app/__init__.py

from japronto import Application
from motor.motor_asyncio

client = motor.motor_asyncio.AsyncIOMotorClient()
db = client.mydb

async def index(request):
    result = await db.find_one()
    print(result)
    return request.Response(text=str(result), mime_type='text/html')

def create_app():
   app = Application()
   app.router.add_route('/', index)

manage.py

from app import create_app

if __name__ == '__main__':
   app = create_app()
   app.run(debug=True)

When I ran it, I got an exception:

RuntimeError: Task <Task pending coro=<pkg() running at  .../app/__init__.py:64> cb=[Pipeline._task_done()]> got Future <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /miniconda/envs/flecom/lib/python3.6/asyncio/futures.py:407]> attached to a different loop

I suspect putting client = motor.motor_asyncio.AsyncIOMotorClient() inside index would work, but that would create new connections for every request. Reusing connection would be more preferable.

[vladz]

Try this:

import asyncio
from japronto import Application
from motor.motor_asyncio

def create_app():
   app = Application()
   event_loop = asyncio.get_event_loop()
   client = motor.motor_asyncio.AsyncIOMotorClient(io_loop=event_loop)
   db = client.mydb
   async def index(request):
      result = await db.find_one()
      print(result)
      return request.Response(text=str(result), mime_type='text/html')
   app.router.add_route('/', index)

[hieu-n]

@vladz Thank you for your response. I tried and still got RuntimeError: Task ... got Future <Future pending cb=[_chain_future.<locals>._call_check_cancel() at ... attached to a different loop.

[vladz]

And if you change the code for this one?

from japronto import Application
from motor.motor_asyncio

def create_app():
   app = Application()
   event_loop = app.loop  # <<--
   client = motor.motor_asyncio.AsyncIOMotorClient(io_loop=event_loop)
   db = client.mydb
   async def index(request):
      result = await db.find_one()
      print(result)
      return request.Response(text=str(result), mime_type='text/html')
   app.router.add_route('/', index)
   app.run()

The idea is to catch a event_loop from japronto and use it in motor.

[squeaky-pl]

What you are doing will result in undefined behavior because Japronto is a pre-forking server and if you set your loop up in the parent process and then fork things will go terribly wrong. There is no official API to do it at the moment.

[squeaky-pl]

If you really want to hack you can override: https://github.com/squeaky-pl/japronto/blob/master/src/japronto/app/__init__.py#L159. This function is called from new process already, you can grab the loop after this is configured and setup your mongodb driver there.

[vladz]

@squeaky-pl Thank you for comments.