Mongodb查询根据upvotes数组的长度对答案进行排序？

Question

我正在尝试编写一个 Mongodb 查询来根据 upvotes 数组的长度对答案进行排序。有更多赞成票的答案应该排在第一位。谁能帮我查询一下？

这是我的收藏对象：

{
    "_id": {
        "$oid": "607fcba8a6b6db2830060a2b"
    },
    "userID": {
        "$oid": "60782e1d4709d515c0684c45"
    },
    "title": "que3",
    "description": "text message",
    "crowdID": "6042142f5a6e0d1d7e694534",
    "userType": "Professional",
    "answers": [
        {
            "_id": {
                "$oid": "607fcbb5a6b6db2830060a2d"
            },
            "userID": {
                "$oid": "60782e004709d515c0684c44"
            },
            "body": "que6",
            "comments": [],
            "date": {
                "$date": "2021-04-21T06:52:37.906Z"
            },
            "upvotes": []
        },
        {
            "_id": {
                "$oid": "607fcbb6a6b6db2830060a2f"
            },
            "userID": {
                "$oid": "60782e004709d515c0684c44"
            },
            "body": "que6",
            "comments": [],
            "date": {
                "$date": "2021-04-21T06:52:38.706Z"
            },
            "upvotes": [
                {
                    "_id": {
                        "$oid": "607fcbefa6b6db2830060a31"
                    },
                    "userID": {
                        "$oid": "607933e4d281292298c99025"
                    },
                    "date": {
                        "$date": "2021-04-21T06:53:35.115Z"
                    }
                },
                {
                    "_id": {
                        "$oid": "607fcc01a6b6db2830060a33"
                    },
                    "userID": {
                        "$oid": "60782e1d4709d515c0684c45"
                    },
                    "date": {
                        "$date": "2021-04-21T06:53:53.641Z"
                    }
                }
            ]
        },
        {
            "_id": {
                "$oid": "607fcc14a6b6db2830060a35"
            },
            "userID": {
                "$oid": "60782e004709d515c0684c44"
            },
            "body": "que6",
            "comments": [],
            "date": {
                "$date": "2021-04-21T06:54:12.492Z"
            },
            "upvotes": []
        },
        {
            "_id": {
                "$oid": "607fcc15a6b6db2830060a37"
            },
            "userID": {
                "$oid": "60782e004709d515c0684c44"
            },
            "body": "que6",
            "comments": [],
            "date": {
                "$date": "2021-04-21T06:54:13.149Z"
            },
            "upvotes": []
        }
    ],
    "date": {
        "$date": "2021-04-21T06:52:24.964Z"
    },
    "__v": 4

Answer 1

终于在 mongo 进行了 4 天的研究后，我创建了一个查询，可以根据需要对嵌套数据进行排序：

db.Question.aggregate([  
    { "$match" : {  "_id": ObjectId(req.params.questionId) }} , 
    {
      $lookup: {
        from: "users",
        localField: "userID",
        foreignField: "_id",
        as: "user_data"
      }
    },
    { $unwind: { "path": "$answers", "preserveNullAndEmptyArrays": true } },
    {
      $lookup: {
        from: "users",
        localField: "answers.userID",
        foreignField: "_id",
        as: "answer_user_data"
      }
    },
    { $unwind: { "path": "$answers.comments", "preserveNullAndEmptyArrays": true } },
    {
      $lookup: {
        from: "users",
        localField: "answers.comments.userID",
        foreignField: "_id",
        as: "comment_user_data"
      }
    },
    {
      $project: {
        _id : 1,
        title : 1,
        description:1,
        crowdId: 1,
        date:1,
        user_data: { "$arrayElemAt": [ "$user_data", 0 ] },
        answers: 
        { 
          $cond: 
          { 
            if: { $gt : [ "$answers._id", 0 ]}, 
            then: [{
              _id: "$answers._id",
              body: "$answers.body",
              date: "$answers.date",
              upvotes_count: { $cond: { if: { $isArray: "$answers.upvotes" }, then: { $size: "$answers.upvotes" }, else: "0"} },
              user_data:{ "$arrayElemAt": [ "$answer_user_data", 0 ] },
              comments: 
              { 
                $cond: 
                { 
                  if: { $gt : [ "$answers.comments._id", 0 ]}, 
                  then: [{
                    _id: "$answers.comments._id",
                    body: "$answers.comments._id",
                    date: "$answers.comments._id",
                    user_data:{ "$arrayElemAt": [ "$comment_user_data", 0 ] },
                  }], 
                  else: [] 
                } 
              }
            }], 
            else: [] 
          } 
        }
      }
    },
    {
      $sort : {
        "answers.upvotes_count": -1,
        "answers.user_data.type": -1,
      }
    },
    {
      $group: {
          _id: '$_id',
          "title": { "$first": "$title" },
          "description": { "$first": "$description" },
          "crowdId": { "$first": "$crowdId" },
          "date": { "$first": "$date" },
          "user_data": { "$first": "$user_data" },
          "answers": { "$push": { $first : "$answers"} },
      }
    }        
      
  ])

上述查询将根据每个答案对象中的赞成票对我的嵌套答案进行排序，并从问题、答案和 cmets 中引用的嵌套“userId”中获取嵌套用户数据。

排序基于投票数和用户类型。如果答案具有相同数量的赞成票，则用户类型“专业”的答案将位于顶部。