Invalid operator '$size' in aggregation

Question

I got the following piece of code:

from pymongo import MongoClient
client = MongoClient(\'ipOfServer\')
db = client.admin
db.authenticate(\'login\', \'password\         


        

Answer 1

The reason is because the $size array aggregation operator is new in MongoDB 2.6 and you are actually running MongoDB 2.4.

I suggest you upgrade your MongoDB server to at least 3.0. But if for some reason you don't want to upgrade now, you will need to $unwind the "players" array and $group by "_id" then return the count using the $sum accumulator operator.

heh = list(db.events.aggregate(
    [
        {"$match": {"status": 'start'}},
        {"$group": {"_id": "$eventName", "players": {"$addToSet": "$uid"}}},
        {"$unwind": "$players"},
        {"$group": {"_id": "$_id", "Count": {"$sum": 1}}},
    ]))