Pymongo and hint, OperationFailure: database error: bad hint

[srounet]

There is an issue in the latest pymongo driver ( 2.1.1 ) and the usage
of hint.

It seems that the hint command refuse any index_name and raise an
OperationFailure.

Reading the documentation (http://api.mongodb.org/python/current/api/
pymongo/cursor.html?highlight=hint#pymongo.cursor.Cursor.hint) it
should be used like this:

>> cursor.hint([('index_name', pymongo.ASCENDING)])

but it fail and raise an Exception.

>> pymongo.errors.OperationFailure: database error: bad hint


To reproduce the problem I have posted an example here:
http://nopaste.info/a63201cae6.html.

The steps to reproduce the Exception are just simple, if you already
have a collection, just try to use hint on it with an existing
index_name and it will fail.

You can try the exact same process in the mongo interpreter and it
will just work.

[Bernie Hackett]

PyMongo doesn't support passing an index "name" for hint. You have to
pass the index spec. This works:

dummy_collection.find().hint([('title', pymongo.ASCENDING)])

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[srounet]

Thank you, I think it can be useful to provide an example below the
description of this method as the usage differ from what we've used to
in the mongo shell.

[A. Jesse Jiryu Davis]

Hi, sorry you've had this trouble. The documentation, here:

http://api.mongodb.org/python/current/api/pymongo/cursor.html?highlight=hint#pymongo.cursor.Cursor.hint

... says:

"index should be an index as passed to create_index() (e.g. [('field',
ASCENDING)]). If index is None any existing hints for this query are
cleared. The last hint applied to this cursor takes precedence over
all others."

Let me know if you can think of a way to improve the docs.

[Valery]

Hi Bernie,

четверг, 23 февраля 2012 г., 16:53:26 UTC+1 пользователь Bernie Hackett написал:

PyMongo doesn't support passing an index "name" for hint. You have to
pass the index spec. This works:

dummy_collection.find().hint([('title', pymongo.ASCENDING)])

in my case it doesn't work either:

>>>> rs = list(my_coll.find({'my_field' : 2177}, limit=1).hint([('my_field', pymongo.ASCENDING)]))

Traceback (most recent call last):

  File "<console>", line 1, in <module>

  File "pymongo/cursor.py", line 778, in next

    if len(self.__data) or self._refresh():

  File "pymongo/cursor.py", line 729, in _refresh

    self.__uuid_subtype))

  File "pymongo/cursor.py", line 686, in __send_message

    self.__uuid_subtype)

  File "pymongo/helpers.py", line 104, in _unpack_response

    error_object["$err"])

OperationFailure: database error: bad hint

>>>> my_coll.index_information()

{u'_id_': {u'key': [(u'_id', 1)], u'v': 1},

 u'my_field_1': {u'key': [(u'my_field', 1)],

                         u'safe': True,

                         u'v': 0}}

>>>> pymongo.version # installed today for pypy, albeit also reproduced with cpython 2.7.1/pymongo 2.1

'2.3+'

kind regards

Valery

[Bernie Hackett]

I've tried reproducing your problem and can't:

>>> coll.ensure_index([('my_field', pymongo.ASCENDING)], safe=True, v=0)
u'my_field_1'
>>> pprint.pprint(coll.index_information())

{u'_id_': {u'key': [(u'_id', 1)], u'v': 1},
u'my_field_1': {u'key': [(u'my_field', 1)], u'safe': True, u'v': 0}}

>>> list(coll.find({'my_field': 2177}, limit=1).hint([('my_field', pymongo.ASCENDING)]))
[{u'my_field': 2177, u'_id': ObjectId('5044c7fa27e9c51134cade12')}]
>>> pymongo.version
'2.3+'

What version of MongoDB are you using?

BTW, safe=True is not needed with ensure_index (and ends up creating a
bogus index option if you pass it). The method always creates the
index with a safe write. I would also suggest you always use version 1
indexes instead of version 0. Your ensure_index call should just be:

coll.ensure_index([('my_field', pymongo.ASCENDING)])

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