python-motor: asyncio driver seems not working

[imbolc]

import asyncio

from motor.motor_asyncio import AsyncIOMotorClient

db = AsyncIOMotorClient().client.motor_asyncio

@asyncio.coroutine

def async_func(loop):

    yield from db.test.remove()

    yield from db.test.insert({'foo': 111})

    x = yield from db.test.find_one()

    print(x)

    yield from db.test.find()

loop = asyncio.get_event_loop()

loop.run_until_complete(async_func(loop))

Causes the exception:

{'foo': 111, '_id': ObjectId('55a641f7444bcb19b0e18a7e')}

Traceback (most recent call last):

  File "test_motor.py", line 20, in <module>

    loop.run_until_complete(async_func(loop))

  File "/home/imbolc/.pyenv/versions/3.4.3/lib/python3.4/asyncio/base_events.py", line 316, in run_until_complete

    return future.result()

  File "/home/imbolc/.pyenv/versions/3.4.3/lib/python3.4/asyncio/futures.py", line 275, in result

    raise self._exception

  File "/home/imbolc/.pyenv/versions/3.4.3/lib/python3.4/asyncio/tasks.py", line 234, in _step

    result = coro.throw(exc)

  File "test_motor.py", line 16, in async_func

    yield from db.test.find()

RuntimeError: Task got bad yield: MotorCursor(<pymongo.cursor.Cursor object at 0x7f4dde7cd9e8>)

Exception ignored in: 

shell returned 1

[A. Jesse Jiryu Davis]

Hi, Motor's asyncio support is in development now, please don't rely on it.

However, in this specific case, "find" does work. Refer to this test case for proper usage of "find":

https://github.com/mongodb/motor/blob/master/test/asyncio_tests/test_asyncio_cursor.py#L39

Correct example:

@asyncio.coroutine

def async_func(loop):

    cursor = db.test.find()

    while (yield from cursor.fetch_next):

        doc = cursor.next_object()

[imbolc]

Thank you. Is it final find api? Is there any reasons don't use obvious syntax that i suggested above?

[A. Jesse Jiryu Davis]

Yes it's final. The reason "find()" doesn't return a list of all documents in the result set is that the list might be very large, and hurt your application's responsiveness and memory usage. So I emphasize APIs that limit the amount of time and memory your application spends retrieving each batch of documents.

If you're certain the list won't be large, use "yield collection.find().to_list(length=None)" to get all documents in one call:

http://motor.readthedocs.org/en/stable/api/motor_cursor.html#motor.MotorCursor.to_list

But if your collection is large and you make a mistake in your query, you'll buffer a large number of documents in RAM. Use wisely. The examples in the tutorial all show safer methods for getting lists of documents.

(Replace "yield" with "yield from" and make other adjustments for asyncio, of course. The docs still only cover Tornado.)

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[Imbolc]

Got it. Thank you very much for detailed explanation.

> https://groups.google.com/d/msgid/mongodb-user/CAL%2BCuuTV8%3DM7O%3D8UTkihGGGPhP1Gb_xE%2Bd6jrigvTHcDRnoWAQ%40mail.gmail.com.