从用户聊天中获取每个用户的最后一个文档 - mongoose答案

【问题标题】：Get last document from userchat for each user - mongoose从用户聊天中获取每个用户的最后一个文档 - mongoose
【发布时间】：2021-05-28 12:20:22
【问题描述】：

用户架构

const userSchema = new Schema({
  name: { type: String, required: true },
  phoneno: { type: String },
  email: { type: String },
  password: { type: String },
  profilePic: { type: String },
  socketId: { type: String },
});
module.exports = mongoose.model("User", userSchema);

用户聊天架构

const userChatSchema = new Schema({
  message: { type: String, required: true },
  sender: { type: Schema.Types.ObjectId, required: true, ref: "User" },
  receiver: { type: Schema.Types.ObjectId, required: true, ref: "User" },
  time: { type: Date, required: true },
});
module.exports = mongoose.model("UserChat", userChatSchema);

我需要一个查询来仅获取当前登录用户与所有其他用户的最后一个用户聊天，即当前登录用户可以是发送者或接收者的聊天，所有其他用户也可以是发送者或接收者，并且该聊天必须是最新登录用户和其他用户之间的聊天。

User and UserChat collections

例如如果当前登录的用户是ObjectId("6039c2513b3fd51f3595d82f")，那么查询必须给出以下输出：

[
  {
    _id: ObjectId("6039c2393b3fd51f3595d82e"),
    name: "userONE",
    phoneno: "123456",
    latestMsg: {
      _id: ObjectId("6039c2df3b3fd51f3595d833"),
      message: "from userONE to userTWO 1",
      receiver: ObjectId("6039c2513b3fd51f3595d82f"), // logged in user
      sender: ObjectId("6039c2393b3fd51f3595d82e"),
      time: ISODate("2021-02-27T03:56:15.122Z"),
    },
  },
  {
    _id: ObjectId("6039c25c3b3fd51f3595d830"),
    name: "userTHREE",
    phoneno: "12345678",
    latestMsg: {
      _id: ObjectId("6039c60ea8061225286e57e4"),
      message: "from userTWO to userTHREE 4",
      receiver: ObjectId("6039c25c3b3fd51f3595d830"),
      sender: ObjectId("6039c2513b3fd51f3595d82f"), // logged in user
      time: ISODate("2021-02-27T04:09:50.579Z"),
    },
  },
  {
    _id: ObjectId("6039c2673b3fd51f3595d831"),
    name: "userFOUR",
    phoneno: "123456789",
    latestMsg: {
      _id: ObjectId("6039c5f2a8061225286e57e2"),
      message: "from userFOUR to userTWO 3",
      receiver: ObjectId("6039c2513b3fd51f3595d82f"), // logged in user
      sender: ObjectId("6039c2673b3fd51f3595d831"),
      time: ISODate("2021-02-27T04:09:22.283Z"),
    },
  },
]

【问题讨论】：

如果您可以共享示例数据、您正在尝试的代码和预期的结果将会很棒:) Mongo playground 将是一个方便的工具。
供用户收藏[link]mongoplayground.net/p/vHjuYNJf4Oi
for UserChat 收藏 [link]mongoplayground.net/p/OvFz4Ao4wZe
可以在 Mongo Playground 中定义多个集合：db={ "User": [ {},... ], "UserChat ": [ {},... ] }

标签： node.js mongodb mongoose mongodb-query aggregation-framework

【解决方案1】：

答案场景：

总共三个用户。
Prakash1、Prakash2 已与 Dheemanth 聊天两次。
Dheemanth 已回复 Prakash1，因此 Dheemanth 的回复是显示的最后一条消息。
Dheemanth 没有回复 Prakash2，因此显示了 Prakash2 的最后一条消息。

查询：

db.users.aggregate([
    {
        $match: {
            _id: ObjectId("6039437ce0c7d52970d3f9f3") // Loged in user _id
        }
    },
    {
        $lookup: {
            from: "chats",
            let: { user_id: "$_id" },
            pipeline: [
                {
                    $match: {
                        $expr: {
                            $or: [
                                { $eq: ["$receiver", "$$user_id"] },
                                { $eq: ["$sender", "$$user_id"] }
                            ]
                        }
                    }
                },
                {
                    $sort: { time: -1 }
                },
                {
                    $group: {
                        _id: {
                            $concat: [
                                { $toString: { $min: ["$sender", "$receiver"] } },
                                { $toString: { $max: ["$sender", "$receiver"] } }
                            ]
                        },
                        sender: { $first: "$sender" },
                        receiver: { $first: "$receiver" },
                        message: { $first: "$message" },
                        time: { $first: "$time" }
                    }
                }
            ],
            as: "latestMsg"
        }
    },
    { $unwind: "$latestMsg" }
]);

输出：用于 Dheemanth

/* 1 createdAt:2/27/2021, 12:22:44 AM*/
{
    "_id" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "name" : "Dheemanth",
    "latestMsg" : {
        "_id" : "6039437ce0c7d52970d3f9f36039437ce0c7d52970d3f9f5",
        "sender" : ObjectId("6039437ce0c7d52970d3f9f5"),
        "receiver" : ObjectId("6039437ce0c7d52970d3f9f3"),
        "message" : "Can u help me?",
        "time" : ISODate("2021-02-27T00:38:00.000+05:30")
    }
},

/* 2 createdAt:2/27/2021, 12:22:44 AM*/
{
    "_id" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "name" : "Dheemanth",
    "latestMsg" : {
        "_id" : "6039437ce0c7d52970d3f9f36039437ce0c7d52970d3f9f6",
        "sender" : ObjectId("6039437ce0c7d52970d3f9f3"),
        "receiver" : ObjectId("6039437ce0c7d52970d3f9f6"),
        "message" : "Ok paste your query.",
        "time" : ISODate("2021-02-27T00:41:00.000+05:30")
    }
}

输出：对于 Prakash1

{
    "_id" : ObjectId("6039437ce0c7d52970d3f9f6"),
    "name" : "Prakash1",
    "latestMsg" : {
        "_id" : "6039437ce0c7d52970d3f9f36039437ce0c7d52970d3f9f6",
        "sender" : ObjectId("6039437ce0c7d52970d3f9f3"),
        "receiver" : ObjectId("6039437ce0c7d52970d3f9f6"),
        "message" : "Ok paste your query.",
        "time" : ISODate("2021-02-27T00:41:00.000+05:30")
    }
}

测试数据：

用户

/* 1 createdAt:2/27/2021, 12:22:44 AM*/
{
    "_id" : ObjectId("6039437ce0c7d52970d3f9f6"),
    "name" : "Prakash1"
},

/* 2 createdAt:2/27/2021, 12:22:44 AM*/
{
    "_id" : ObjectId("6039437ce0c7d52970d3f9f5"),
    "name" : "Prakash2"
},

/* 3 createdAt:2/27/2021, 12:22:44 AM*/
{
    "_id" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "name" : "Dheemanth"
}

聊天

/* 1 createdAt:2/27/2021, 1:21:05 PM*/
{
    "_id" : ObjectId("6039f9e9e0c7d52970d3fa43"),
    "sender" : ObjectId("6039437ce0c7d52970d3f9f6"),
    "receiver" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "message" : "Hi im am Prakash1",
    "time" : ISODate("2021-02-27T00:39:00.000+05:30")
},

/* 2 createdAt:2/27/2021, 1:21:05 PM*/
{
    "_id" : ObjectId("6039f9e9e0c7d52970d3fa44"),
    "sender" : ObjectId("6039437ce0c7d52970d3f9f6"),
    "receiver" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "message" : "Need some help!!!",
    "time" : ISODate("2021-02-27T00:40:00.000+05:30")
},

/* 3 createdAt:2/27/2021, 1:21:05 PM*/
{
    "_id" : ObjectId("6039f9e9e0c7d52970d3fa45"),
    "sender" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "receiver" : ObjectId("6039437ce0c7d52970d3f9f6"),
    "message" : "Ok paste your query.",
    "time" : ISODate("2021-02-27T00:41:00.000+05:30")
},

/* 4 createdAt:2/27/2021, 1:21:05 PM*/
{
    "_id" : ObjectId("6039f9e9e0c7d52970d3fa46"),
    "sender" : ObjectId("6039437ce0c7d52970d3f9f5"),
    "receiver" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "message" : "Hi im am Prakash2",
    "time" : ISODate("2021-02-27T00:37:00.000+05:30")
},

/* 5 createdAt:2/27/2021, 1:21:05 PM*/
{
    "_id" : ObjectId("6039f9e9e0c7d52970d3fa47"),
    "sender" : ObjectId("6039437ce0c7d52970d3f9f5"),
    "receiver" : ObjectId("6039437ce0c7d52970d3f9f3"),
    "message" : "Can u help me?",
    "time" : ISODate("2021-02-27T00:38:00.000+05:30")
}

【讨论】：

您的查询返回当前登录用户收到的最新聊天，我想要的是返回当前登录用户和其他用户之间的最新聊天的查询，以便该聊天的接收者可以是当前登录的用户或其他用户，这也适用于所有其他用户。
OK 检查修改后的查询和结果。这必须有效！
进一步如果您需要排序，例如：每个用户的最后一条消息中的最新消息，您可以在$unwind之后的末尾添加另一个阶段{ $sort: { "latestMsg.time": -1 } }。
谢谢。有效。我们如何在输出中填充 sender 和 receiver 字段？
在主外部 $lookup 内执行两个单独的 $lookups 到 users 集合。