MongoDB 4.2: mongoengine.errors.OperationError: Update failed (BSON field 'no_cursor_timeout' is an unknown field.)

[crunk1]

mongoengine.errors.OperationError: Update failed (BSON field 'no_cursor_timeout' is an unknown field.)
    at modify (/opt/python3.7/lib/python3.7/site-packages/mongoengine/queryset/base.py:650)

Sorry, don't have exact steps to repro this. Caught this as we were trying out 4.2 and I'm busy reverting back to 4.0 :)

Some basic info:
python: 3.7.4
mongoengine: 0.18.2
pymongo: 3.9.0

Error does not appear when running against server 4.0.12.
Upon upgrading to 4.2, error starts popping up during update queries.

[kingb]

We ran into the same problem.

[ghost]

This seems to be an undocumented breaking change in Mongo 4.2. Should this be reported as a bug on that side?

On another note, pymongo only documents no_cursor_timeout for some operations, so perhaps this was never supported for update?

In any case, the problem is caused by this: https://github.com/MongoEngine/mongoengine/blob/master/mongoengine/queryset/base.py#L1579

Mongoengine always adds no_cursor_timeout, the only thing that changes is whether it's true or false. This is most likely the wrong thing to do.