Mongo Aggregation返回其中一个key：value的[{}]

Question

我使用NodeJS，ExpressJS和Mongoose Mongo ORM。

我的架构如下。

const chatMessageSchema = new Schema({
  _id: { 
   type: String,
   default: () => (uuidV1().replace(/-/g, ''))
  },
  roomid: String,
  message: Schema.Types.Mixed,
  type: String, // text, card, qrt, attachment
  notes: [notesSchema],
  posted_by_user: String,
}, { 
  timestamps: { 
    createdAt: 'created_at',
    updatedAt: 'updated_at' 
}, 
  collection: 'ChatMessages'
});

注释的嵌套子模式如下;

const notesSchema = new Schema({
    _id: { 
      type: String,
      default: () => (uuidV1().replace(/-/g, ''))
    },
    roomid: String,
    messageid: String,
    message: Schema.Types.Mixed,
    type: String, // text, attachment
    posted_by_user: String,
}, { 
  timestamps: { 
    createdAt: 'created_at',
    updatedAt: 'updated_at' 
}});

最初，当用户创建chatMessage时，注释默认最初保存为空数组[]。

用户可以在创建消息后显式创建注释消息，注释是数组子文档。

现在发生的事情就是当我得到一个消息列表时。我需要显示posted_by_user这是一个字符串的id。对于该字符串的id，我执行$lookup获取用户配置文件。聚合如下。

return this.aggregate([
  { $match : {roomid: roomid} },
  { $sort: {created_at: -1} },
  {
    $lookup: {
      from: "RefUserProfiles",
      localField: "posted_by_user",
      foreignField: "_id",
      as: "posted_by_user"
    }
  },
  { $unwind: "$posted_by_user" },
  { $skip: pageOptions.page * pageOptions.limit },
  { $limit: pageOptions.limit },
  { $sort: {created_at: 1} },

  { 
    $unwind: {  path: "$notes", preserveNullAndEmptyArrays: true }  
  },
  {
    $lookup: {
      from: "RefUserProfiles",
      localField: "notes.posted_by_user",
      foreignField: "_id",
      as: "notes.posted_by_user"
    }
  },
  { 
    $unwind: { path: "$notes.posted_by_user", preserveNullAndEmptyArrays: true } 
  },
  {
    $group: {
      _id: "$_id",
      created_at: { $last: "$created_at" },
      roomid: { $last: "$roomid" },
      message: { $last: "$message" },
      notes: { $addToSet: "$notes" },
      type: { $last: "$type" },
      posted_by_user: { $last: "$posted_by_user" },
      read_by_recipients: { $last: "$read_by_recipients" },
    }
  }
]);

现在，因为在某些情况下，某些消息的注释是一个空数组，因此对于非常特殊的情况，我在响应中得到的对象就像[{}]。是这样的假设。或者是否有更好的用例。

例如，我根据此查询获得的响应如下。

"conversation": [  
    {
        "_id": "7cdbf630e6ec11e79166559abfb987ac",
        "created_at": "2017-12-22T07:48:23.956Z",
        "roomid": "aacc6b70e68211e79166559abfb987ac",
        "message": {
            "text": "message 1"
        },
        "notes": [{}],
        "type": "text",
        "posted_by_user": {
            "id": "4d6fd5a95d57436d944586a1d5b2b2ff",
            "name": "Adeel Imran",
            "profilePicture": "",
            "phone": "",
            "email": "",
            "designation": "",
            "type": "user"
        },
    },
    {
        "_id": "80d91470e6ec11e79166559abfb987ac",
        "created_at": "2017-12-22T07:48:30.648Z",
        "roomid": "aacc6b70e68211e79166559abfb987ac",
        "message": {
            "text": "message 4"
        },
        "notes": [
           {
                "posted_by_user": {
                    "id": "86049b3d28f640a8a6722c57b73a292e",
                    "name": "Paul Johnson",
                    "profilePicture": "",
                    "phone": "",
                    "email": "",
                    "designation": "",
                    "type": "sp"
                },
                "type": "text",
                "message": {
                    "text": "yeah "
                },
                "messageid": "26401d30e5a511e7acc4c734d11adb25",
                "roomid": "27d3ed80e0cc11e78318b3cd036890f2",
                "updated_at": "2017-12-20T16:45:44.132Z",
                "created_at": "2017-12-20T16:45:44.132Z",
                "_id": "38ad3750e5a511e7acc4c734d11adb25"
            }
        ],
        "type": "text",
        "posted_by_user": {
            "id": "4d6fd5a95d57436d944586a1d5b2b2ff",
            "name": "Adeel Imran",
            "profilePicture":"",
            "phone": "",
            "email": "",
            "designation": "",
            "type": "user"
        },
    }
],

对此有任何建议或指示将受到高度赞赏。感谢您抽出宝贵时间来回顾这个问题。

干杯。