如何从mongodb的聊天对话中获取最新消息 [英] How to get last message from chat conversation in mongodb

问题描述

我试图获取用户之间聊天中的最后一条消息。
以下是我在文档中的收藏集。

I have tried to get last message in chat between users. Below is my collections in my document.

{
"toUser":123,"fromUser":456,"message":"1 from suresh","timeStamp":"2019-10-09 16:39:14:1414 PM +05:30",

"toUser":456,"fromUser":123,"message":"Man super man ","timeStamp":"2019-10-09 16:43:09:0909 PM +05:30",

"toUser":456,"fromUser":123,"message":"Kk","timeStamp":"2019-10-09 18:31:12:1212 PM +05:30"

"toUser":456,"fromUser":123,"message":"It working man","timeStamp":"2019-10-09 18:31:18:1818 PM +05:30"

"toUser":456,"fromUser":123,"message":"2","timeStamp":"2019-10-09 18:31:21:2121 PM +05:30"

"toUser":101,"fromUser":123,"message":"Kk","timeStamp":"2019-10-09 18:31:12:1212 PM +05:30"
} 

而我使用mongo查询为

and i used mongo query as

db.chats.aggregate(
[
    {$match:{$or:[{"toUser":123},{"fromUser":123}]}},
    { "$sort": { "timeStamp": -1}},    
    {
        "$group": {
           "_id": {fromUser:"$fromUser",toUser:"$toUser"},
           "fromUser": {"$first":"$fromUser"},
           "toUser" : {"$first":"$toUser"},
           "message": {"$first": "$message" },
            "timeStamp": { "$first": "$timeStamp"}
        }
    },
]
);

我的输出是

{ "_id" : { "fromUser" : 456, "toUser" : 123 }, "fromUser" : 456, "toUser" : 123, "message" : "1 from suresh", "timeStamp" : "2019-10-09 16:39:14:1414 PM +05:30" }
{ "_id" : { "fromUser" : 123, "toUser" : 101 }, "fromUser" : 123, "toUser" : 101, "message" : "Kk", "timeStamp" : "2019-10-09 18:31:12:1212 PM +05:30" }
{ "_id" : { "fromUser" : 123, "toUser" : 456 }, "fromUser" : 123, "toUser" : 456, "message" : "2", "timeStamp" : "2019-10-09 18:31:21:2121 PM +05:30" }

但是如果您查看的是介于123和456之间的实际最后一条消息用户是消息：2

But If you look actual last message between 123 and 456 users is message:2

所以我需要按时间戳排序的最终输出如下。

so I need final output as below sorted on timestamp.

{ "_id" : { "fromUser" : 123, "toUser" : 456 }, "fromUser" : 123, "toUser" : 456, "message" : "2", "timeStamp" : "2019-10-09 18:31:21:2121 PM +05:30" }
{ "_id" : { "fromUser" : 123, "toUser" : 101 }, "fromUser" : 123, "toUser" : 101, "message" : "Kk", "timeStamp" : "2019-10-09 18:31:12:1212 PM +05:30" }

有人可以帮助我解决该查询吗。

Can anybody help me to solve the query.

请先谢谢。

推荐答案

问题是存储消息的方式。

存储的数据：

fromUser 123 and toUser 456
fromUser 456 and toUser 123

因此，当您将其分组时，在逻辑上 它们是相同的 ，但不是用于分组。

So, when you group it, logically they are same, but not for grouping.

解决方案：

我们需要确保发送方/接收方总是以相同的方式出现

We need to ensure that sender / receiver comes always in the same way

1. Create array where we store sender / receiver
2. Order that array `[123, 456] [456, 123] => [123,456], [123,456]`
3. Group by this ordered array (In Mongo way: $project, $unwind, $sort, $group - push)

---

---

db.chats.aggregate([
  {
    $match: {
      $or: [
        {
          "toUser": 123
        },
        {
          "fromUser": 123
        }
      ]
    }
  },
  {
    "$project": {
      toUser: 1,
      fromUser: 1,
      message: 1,
      timeStamp: 1,
      fromToUser: [
        "$fromUser",
        "$toUser"
      ]
    }
  },
  {
    $unwind: "$fromToUser"
  },
  {
    $sort: {
      "fromToUser": 1
    }
  },
  {
    $group: {
      _id: "$_id",
      "fromToUser": {
        $push: "$fromToUser"
      },
      "fromUser": {
        "$first": "$fromUser"
      },
      "toUser": {
        "$first": "$toUser"
      },
      "message": {
        "$first": "$message"
      },
      "timeStamp": {
        "$first": "$timeStamp"
      }
    }
  },
  {
    "$sort": {
      "timeStamp": -1
    }
  },
  {
    "$group": {
      "_id": "$fromToUser",
      "fromUser": {
        "$first": "$fromUser"
      },
      "toUser": {
        "$first": "$toUser"
      },
      "message": {
        "$first": "$message"
      },
      "timeStamp": {
        "$first": "$timeStamp"
      }
    }
  }
])

---

结果

[
  {
    "_id": [
      101,
      123
    ],
    "fromUser": 123,
    "message": "Kk",
    "timeStamp": "2019-10-09 18:31:12:1212 PM +05:30",
    "toUser": 101
  },
  {
    "_id": [
      123,
      456
    ],
    "fromUser": 123,
    "message": "2",
    "timeStamp": "2019-10-09 18:31:21:2121 PM +05:30",
    "toUser": 456
  }
]

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