MongoDB:$divide 和 $multiply 出错

Question

我正在创建一个 MongoDB 聚合管道，但我被困在这个阶段:

        $group: {
            _id: {checkType: "$_id.checkType", resultCode: "$_id.resultCode"},
            count: { $sum: "$count" },
            ctv: { $sum: "$ctv" },
            perc:{$multiply:[{$divide:["$ctv","$count"]},100]},
            weight: { $divide: [ "$ctv", "$count"] },
            details: { $push: "$$ROOT" }
        }

它给出错误“$multiply 累加器是一元运算符”。同样，如果我用 $multiply 删除该行，我会在下一行得到“$divide 累加器是一元运算符”。我在网上找不到这个错误的描述。我的语法有什么问题？

Answer 1

arithmetic operators不能用作 $group accumulators .将它们移至另一个 $project 流水线阶段为:

db.collection.aggregate([
    { "$group": {
        "_id": { "checkType": "$_id.checkType", "resultCode": "$_id.resultCode" },
        "count": { "$sum": "$count" },
        "ctv": { "$sum": "$ctv" },
        "details": { "$push": "$$ROOT" }
    } },
    { "$project": {
        "count": 1,
        "details": 1,
        "ctv": 1,
        "perc": { "$multiply": [ { "$divide": ["$ctv","$count"] }, 100 ] },
        "weight": { "$divide": ["$ctv", "$count"] },
    } }
])

或

如果使用 MongoDB 3.4 及更高版本，请使用 $addFields 而不是 $project

db.collection.aggregate([
    { "$group": {
        "_id": { "checkType": "$_id.checkType", "resultCode": "$_id.resultCode" },
        "count": { "$sum": "$count" },
        "ctv": { "$sum": "$ctv" },
        "details": { "$push": "$$ROOT" }
    } },
    { "$addFields": {
        "perc": { "$multiply": [ { "$divide": ["$ctv","$count"] }, 100 ] },
        "weight": { "$divide": ["$ctv", "$count"] },
    } }
])