PyMongo:Hvordan man bruger aggregat og gemmer resultaterne til en anden samling?

Følgende er den brugbare kode testet på pymongo version 3.6.1 og python 3.6.4

    import pymongo
    from pymongo import MongoClient
    client = MongoClient('127.0.0.1')  # mongodb running locally
    dbRead = client['test']            # using the test database in mongo
    # create the pipeline required 
    pipeline = [{"$match": {"$text": {"$search":"StackOverflow"}}},{"$out":"C_b"}]  # all attribute and operator need to quoted in pymongo
    dbRead.C_a.aggregate(pipeline)  #execution 
    print (dbRead.C_b.count()) ## verify count of the new collection