小编Sai*_*der的帖子

我看教程，我可以理解这种聚合是如何工作的，有什么用pings，$$ROOT在里面。

client = pymongo.MongoClient(MY_URL)
pings = client['mflix']['watching_pings']
cursor = pings.aggregate([
  {
    "$sample": { "size": 50000 }
  },
  {
    "$addFields": { 
      "dayOfWeek": { "$dayOfWeek": "$ts" },
      "hourOfDay": { "$hour": "$ts" }
    }
  },
  {
    "$group": { "_id": "$dayOfWeek", "pings": { "$push": "$$ROOT" } }
  },
  {
    "$sort": { "_id": 1 }
  }
]);