Node.js mongodb（聚合）-$lookup和查找结果

我是聚合框架的新手，有以下问题

我的收藏如下：

用户

    _id: ObjectId('604caef28aa89e769585f0c4')
    baseData: { 
       firstName: "max"
       username: "max_muster"
       ...
       ...
    }

  _id: ObjectId('604caf718aa89e769585f0c8')
 "baseData": {
      "userID":"604caef28aa89e769585f0c4",
      "type":0,
      "title":"Alessandro send you a friend request.",
      "description":"",
      "actionID":"604caef28aa89e769585f0c4"
   },

活动提要

    _id: ObjectId('604cb97c99bbd77b54047370')
    userID: "604caef28aa89e769585f0c4"     // the user id 
    activity: "604caf718aa89e769585f0c8"   // the activity id 
    viewed: false 
    

活动

    _id: ObjectId('604caef28aa89e769585f0c4')
    baseData: { 
       firstName: "max"
       username: "max_muster"
       ...
       ...
    }

  _id: ObjectId('604caf718aa89e769585f0c8')
 "baseData": {
      "userID":"604caef28aa89e769585f0c4",
      "type":0,
      "title":"Alessandro send you a friend request.",
      "description":"",
      "actionID":"604caef28aa89e769585f0c4"
   },

聚合函数

const response = ActivityFeed.aggregate([
      {
        $match: { userID: ObjectId(args.user) },
      },
      {
        $lookup: {
          from: 'activities',
          localField: 'activity',
          foreignField: '_id',
          as: 'lookup_activities',
        },
      },
      { $unwind: '$activities' },
      {
        $lookup: {
          from: 'users',
          localField: 'lookup_activities.baseData.actionID',
          foreignField: '_id',
          as: 'lookup_users',
        },
      },
    ]);

如何使用第一个查找结果进行查找

我查找了“活动”集合。此集合保存第二次查找baseData.userID的id。但是使用这种方法，第二次查找没有结果

我加入activities集合的原因是actionID可以保存另一个集合中的用户id或文档id。它取决于“活动”集合中的类型

在聚合框架中，是否可以根据上一次查找的类型和类型进行查找

---

提前感谢您。

我所做的只是修复您的聚合。您解开了错误的字段，请确保所有ID字段都是ObjectId。如果您不熟悉聚合功能，我强烈建议使用来帮助聚合。他们有一个分阶段的帮助GUI，这会让你的生活更轻松

使用的样本

 db={
  "users": [
    {
      _id: ObjectId("604caef28aa89e769585f0c4"),
      baseData: {
        firstName: "max",
        username: "max_muster"
      }
    }
  ],
  "activitiesFeed": [
    {
      _id: ObjectId("604cb97c99bbd77b54047370"),
      userID: ObjectId("604caef28aa89e769585f0c4"),
      activity: ObjectId("604caf718aa89e769585f0c8"),
      viewed: false
    }
  ],
  "activities": [
    {
      _id: ObjectId("604caf718aa89e769585f0c8"),
      "baseData": {
        "userID": ObjectId("604caef28aa89e769585f0c4"),
        "type": 0,
        "title": "Alessandro send you a friend request.",
        "description": "",
        "actionID": ObjectId("604caef28aa89e769585f0c4")
      },
    }
  ]
}

---

它非常适合我：D谢谢@Koodies你知道是否有可能改变循环结果吗？结果是baseData{….}是否可以删除baseData，结果只是键？是的，请查看$project或$set