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I use Motor driver of mongoDB in my django project and I have problem to convert my data(who comes from database as cursor) to list, here is my code:

documents = db.factor.aggregate([{"$limit": 3},
     {"$lookup": {"from": "subfactor", "localField": "_id", "foreignField": "factor_id", "as": "subfactor"}}])

for d in await list(documents):
    print(d)

and the Error:

File "/usr/lib/python3.8/asyncio/runners.py", line 43, in run
return loop.run_until_complete(main)
File "/usr/lib/python3.8/asyncio/base_events.py", line 595, in run_until_complete
self.run_forever()
File "/usr/lib/python3.8/asyncio/base_events.py", line 563, in run_forever
self._run_once()
File "/usr/lib/python3.8/asyncio/base_events.py", line 1808, in _run_once
event_list = self._selector.select(timeout)
File "/usr/lib/python3.8/selectors.py", line 468, in select
fd_event_list = self._selector.poll(timeout, max_ev)
Amirhossein Azhdari
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  • I have no idea regarding the mongoDB/Django part, but the errors talk about `timeout`s: could that be the problem, maybe the operation is too slow? – Pietro Mar 15 '21 at 11:32
  • @Pietro tnx for your comment, this is not problem, the problem is converting the data who came from mongo to Python code. – Amirhossein Azhdari Mar 15 '21 at 11:42
  • What's your error exactly? You stripped first line of error. Also is cursor iterable? I guess it shouldn't be as library is async based. – Arman Ordookhani Mar 15 '21 at 12:37

1 Answers1

5

I don't know Motor but a quick check in their docs shows this:

Cursor is async iterable, so you can use async for to iterate:

async for document in db.test_collection.find({'i': {'$lt': 2}}):
    pprint.pprint(document)

You can turn this into a list with a async list comprehention:

items = [x async for x in db.test_collection.find({'i': {'$lt': 2}})]

Also they have helper functions to convert a cursor to an awaitable list:

items = await db.test_collection.find({'i': {'$lt': 2}}).to_list(length=100)
Arman Ordookhani
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