node.js - 将对象放置到 mongoDb 中的根级别

Question

我有一个聚合查询，可以从 3 个集合中获取结果。

我使用的是 mongoDb 3.4

来自结果的一个示例文档。

{ 
    "_id" : ObjectId("5ba1717ee4b00ce08ca47cfa"),  
    "name" : "captain jack", 
    "email" : "jack@gmail.com", 
    "mobile" : "9000000023", 
    "status" : "verified", 
    "courses" : [
        {
            "_id" : "13", 
            "name" : "Course (03)"
        },{
            "_id" : "12", 
            "name" : "Course (03)"
        }
    ], 
    "examCompleted" : false, 
    "login" : "5ba1717ee4b00fe08ca47cfa", 
    "partnerMetaInfo" : {
        "_id" : ObjectId("5ba1717ee4b00fe08ca47cfa"), 
        "costCode" : "5761", 
        "hub" : "CALCUTTA", 
        "location" : "Kolkata" 

    }
}

我正在尝试将 partnerMetaInfo 引入根级别。我也无法使用 $match on _id == 13 来过滤 course._id

这是我的聚合查询:

db.getCollection("mainCollection").aggregate([
        {
            //Join two collection
            $lookup:{
                from: "Details",
                localField: "username",
                foreignField: "login",
                as: "partnerData"
            }
        },{
            //Limit fields
            $project:{
                "email":1,
                "name":1,
                "mobile":1,
                "status" : 1,
                "courses":"$partnerData.courses",
                "examScore" : "$partnerData.examScore",
                "examCompleted" : "$partnerData.examCompleted",
                "login":"$partnerData.login"
            }
        },
        {
            //Join third collection
            $lookup:{
                from: "PartnerMetaInfo",
                localField: "login",
                foreignField: "partnerId",
                as: "partnerMetaInfo"
            }
        },
        //Remove from partnerData array and place at root level.
        {
            $unwind:
            {
                path: '$courses',
                preserveNullAndEmptyArrays: true
            }
        },{
            $unwind:
            {
                path: '$examScore',
                preserveNullAndEmptyArrays: true
            }
        },{
            $unwind:
            {
                path: '$examCompleted',
                preserveNullAndEmptyArrays: true
            }
        },{
            $unwind:
            {
                path: '$login',
                preserveNullAndEmptyArrays: true
            }
        },//Bring $partnerMetaInfo array to root level.
        {
            $unwind:
            {
                path: '$partnerMetaInfo',
                preserveNullAndEmptyArrays: true
            }
        },{
            $limit:10
        }
    ];

$unwind 之后的partnerMetaInfo 最终作为对象。我想把它压平并将其放在根部水平。

有人可以帮我解决这个问题吗？

Answer 1

如果您想要获得的结果只是 partnerMetaInfo 字段的内容，那么您只需添加 $replaceRoot管道末端的阶段如下所示:

{
    $replaceRoot: { "newRoot": { $ifNull: [ "$partnerMetaInfo", {} ] } }
}

否则，如果您只想将 partnerMetaInfo 字段内的字段移动到根目录，那么您可以使用 $addFields :

{
    $addFields: {
        "partnerMetaInfoId" : "$partnerMetaInfo._id", 
        "costCode" : "$partnerMetaInfo.costCode", 
        "hub" : "$partnerMetaInfo.hub", 
        "location" : "$partnerMetaInfo.location" 
    }
}

如果您有动态数量的字段或不想对字段名称进行硬编码，则可以使用以下逻辑:

{
    $replaceRoot: { // merge fields of and move them all the way up
        "newRoot": { $mergeObjects: [ "$$ROOT", "$partnerMetaInfo" ] }
    }
}, {
    $project: { // remove the "partnerMetaInfo" field
        "partnerMetaInfo": 0
    }
}