PyMongo C extension + LazyProxy = 💔

[ramnes]

PyMongo does not seem to like LazyProxy objects passed in a query (and most likely in all other places where a dict that will later be serialized to BSON is required).

The bug, in action:

>>> from pymongo import MongoClient
>>> from lazify import LazyProxy
>>> collection = MongoClient().database.collection
>>> collection.find_one({"test": LazyProxy(list)})
... stacktrace ...
InvalidDocument: Cannot encode object: <lazify.LazyProxy object at 0x7f7daa50d990>
>>> 

But surprisingly, it does not happen when the LazyProxy.value is a dict:

>>> # works just as expected (returns nothings)
>>> collection.find_one({"test": LazyProxy(dict)})
>>> 

Also, it's worth noting that the pure-Python version of PyMongo's bson works just as expected:

>>> import sys
>>> sys.modules["bson._cbson"] = None
>>> from pymongo import MongoClient
>>> from lazify import LazyProxy
>>> collection = MongoClient().database.collection
>>> collection = MongoClient().database.collection
>>> collection.find_one({"test": LazyProxy(list)})
>>> 

The issue is most likely an incompatible way of checking the query contents type somewhere in pymongo/bson/_cbsonmodule.c.

Versions in place:

Lazify==0.4.0
pymongo==3.7.1

[ramnes]

Might be related to #4.

[prashantmital]

PyMongo 3.8 (due for release in the next 3-4 weeks) will introduce a new feature for encoding and decoding custom, user-defined types that might help you solve this problem. If you get the chance, you can take a look at an example of this new functionality in action at https://github.com/mongodb/mongo-python-driver/blob/master/doc/examples/custom_type.rst and also test drive it by installing PyMongo from master.

[ramnes]

Thanks @prashantmital!

@trubesv