聚合-用pymongo计数记录

Question

I would like to count matching records with pymongo. I have looked up the documentation: https://docs.mongodb.com/manual/reference/operator/aggregation/group/#group-by-month-day-and-year

I understand that I should do something like:

db.foo_baz.aggregate([{'$group': {'_id': '$baz_id', 'count': {'$sum': 1}}}])

However, I am getting this error:

      File "/usr/lib/python3.6/site-packages/mongomock/collection.py", line 1531, in aggregate
    from_field = key.replace('$', '')
AttributeError: 'int' object has no attribute 'replace'

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I would think that pymongo would evaluate it to this mongodb statement:

 db.foo_baz.aggregate({{$group: {_id: '$baz_id', count: {$sum: 1}}}])

Which gives me the expected result when ran from mongodb console, which is: {"_id" : NumberInt("1234"), "count" : 1} in my case.

What am I doning wrong? I am using pymongo 3.4 and python 3.6 and mongomock 3.7.

I have also tried replacing 1 with "1" which does not crash, but gives an incorrect result: ( {"_id" : NumberInt("1234"), "count" : NumberInt("0")} )

Answer 1

好吧，显然这是mongomock中的错误，升级到3.8后，我得到了预期的行为。