猫鼬聚合不返回最新文档

Question

我有一个返回文档的聚合，但我需要它返回集合 messageTrackingId 中最新的文档。在creationDate 字段中具有最新值的那个我有一种方法可以完成此操作，但我不断收到不是最新的返回文档，我不知道为什么。目的是向用户显示该用户与另一个用户之间发送的最后一条消息的时间戳，无论是谁发送的。感谢任何帮助。

app.get("/api/messages", (req, res, next) => {
  query = {};
  inbox = false;
  messageId = false;
  console.log(req.query.recipientId);
  if (req.query.recipientId) {
    query = { recipientId: req.query.recipientId };
    inbox = true;

    Messages.aggregate([
      {
        $match: {
          $or: [
            { recipientId: req.query.recipientId },
            { creator: mongoose.Types.ObjectId(req.query.recipientId) }
          ]
        }
      },
      {
        $addFields: {
          conversant: {
            $cond: [
              { $ne: ["$recipientId", req.query.recipientId] },
              "$recipientId",
              "$creator"
            ]
          }
        }
      },
      {
        $sort: { creationDate: 1 }
      },
      {
        $group: {
          _id: "$conversant",
          message: { $last: "$message" },
          recipientId: { $last: "$recipientId" },
          creator: { $last: "$creator" },
          messageTrackingId: { $last: "$messageTrackingId" },
          recipient: { $last: "$recipient" },
          creationDate: { $last: "$creationDate" }
        }
      },
      {
        $lookup: {
          from: "users",
          let: { creator: "$creator" },
          pipeline: [
            { $match: { $expr: { $eq: ["$_id", "$$creator"] } } },
            { $project: { instagramName: 1 } }
          ],
          as: "creatorName"
        }
      }
    ]).then(documents => {


      if (inbox === true) {
        res.status(200).json({
          message: "User's Inbox Retrieved!",
          posts: documents
        });
      }

    });

我清理了消息表并来回发送了3条消息进行演示。当我重新加载页面时，我在 JSON 响应中只收到 2 个文档，而不是最新的一个。在收到的 2 个中，它们似乎都不是最新的。我不确定为什么它不返回一个。请参阅下面的页面加载输出。

消息：

/* 1 */
{
    "_id" : "5e16463be5fcba1d2c56ebb7",
    "creator" : "5e0a1d41f86e1e4234fc1a77",
    "recipient" : "andy",
    "recipientId" : "5df0014e25ee451beccf588a",
    "message" : "First message",
    "messageTrackingId" : "17c4fc99-d92f-46ef-9bae-1408f415287a",
    "creatorName" : "buyer1",
    "creationDate" : ISODate("2020-01-08T21:14:35.104Z"),
    "__v" : 0.0
}

/* 2 */
{
    "_id" : "5e16464de5fcba1d2c56ebb9",
    "creator" : "5df0014e25ee451beccf588a",
    "recipient" : "buyer1",
    "recipientId" : "5e0a1d41f86e1e4234fc1a77",
    "message" : "Second Message",
    "messageTrackingId" : "17c4fc99-d92f-46ef-9bae-1408f415287a",
    "creatorName" : "andy",
    "creationDate" : ISODate("2020-01-08T21:14:53.618Z"),
    "__v" : 0.0
}

/* 3 */
{
    "_id" : "5e16465ce5fcba1d2c56ebbb",
    "creator" : "5e0a1d41f86e1e4234fc1a77",
    "recipient" : "andy",
    "recipientId" : "5df0014e25ee451beccf588a",
    "message" : "Third Message",
    "messageTrackingId" : "17c4fc99-d92f-46ef-9bae-1408f415287a",
    "creatorName" : "buyer1",
    "creationDate" : ISODate("2020-01-08T21:15:08.500Z"),
    "__v" : 0.0
}

用户：

/* 1 */
{
    "_id" : "5df00d08c713f722909c99c1",
    "email" : "joe@gmail.com",
    "password" : "$2b$10$5eWhwL4RNT8TyQRCC191J.myYBwFcJ8hCARqGfofYWUmRaq6jJFQm",
    "instagramName" : "joe",
    "over21" : "Yes",
    "role" : "Artist",
    "fullName" : "testdsfdfsfs",
    "address1" : "adfsdf",
    "address2" : "dssdf",
    "city" : "sdfsdfsdf",
    "state" : "dsffsdsd",
    "zip" : "dsdfsdf",
    "passwordCreated" : ISODate("2020-01-07T23:46:57.861Z"),
    "__v" : 0
}

/* 2 */
{
    "_id" : "5df0014e25ee451beccf588a",
    "email" : "andy@gmail.com",
    "password" : "$2b$10$fNHmIoDb4mX6x.YeMLXHbu2yIaeW6HVQvNpZR8Nt/a4xVFkhxM1Ey",
    "instagramName" : "andy",
    "over21" : "Yes",
    "role" : "Artist",
    "fullName" : "dsfdsfdfdsf",
    "address1" : "111",
    "address2" : "111",
    "city" : "atlanta",
    "state" : "ga",
    "zip" : "33222",
    "passwordCreated" : ISODate("2019-12-19T15:29:46.528Z"),
    "__v" : 0
}

必需的输出（返回每个用户的最后一条消息）：

/* 1 */
{
    "_id" : {
        "conversant" : "5df0014e25ee451beccf588a",
        "recipient" : "andy"
    },
    "message" : "Third Message",
    "recipientId" : "5df0014e25ee451beccf588a",
    "creator" : "5e0a1d41f86e1e4234fc1a77",
    "messageTrackingId" : "17c4fc99-d92f-46ef-9bae-1408f415287a",
    "recipient" : "andy",
    "creationDate" : ISODate("2020-01-08T21:15:08.500Z"),
    "creatorName" : [ 
        {
            "_id" : "5df0014e25ee451beccf588a",
            "instagramName" : "andy"
        }
    ]
}

/* 2 */
{
    "_id" : {
        "conversant" : "5df0014e25ee451beccf588a",
        "recipient" : "buyer1"
    },
    "message" : "Second Message",
    "recipientId" : "5e0a1d41f86e1e4234fc1a77",
    "creator" : "5df0014e25ee451beccf588a",
    "messageTrackingId" : "17c4fc99-d92f-46ef-9bae-1408f415287a",
    "recipient" : "buyer1",
    "creationDate" : ISODate("2020-01-08T21:14:53.618Z"),
    "creatorName" : [ 
        {
            "_id" : "5df0014e25ee451beccf588a",
            "instagramName" : "andy"
        }
    ]
}

Answer 1

改变必须是

1) 如果我在这个阶段理解正确，您想在一个字段上按 recipientId 分组（因为您不能对单个值的两个字段分组）所以您正在创建一个名为 conversant 的新字段, 所以它必须是$eq 或者你需要交换recipientId & creator & 也必须是$toString:

{
      $addFields: {
        conversant: {
          $cond: [
            { $eq: ["$recipientId", req.query.recipientId] },
            "$recipientId",
            {$toString : "$creator"} 
          ]
        }
      }
    }

2) 您不需要这个$sort 阶段，因为所有最新添加到集合的内容都将添加到最后（期望creationDate 已创建但从未更新）：

// Not useful
{
     $sort: { creationDate: 1 }
}

您还需要按_id: { conversant: "$conversant", recipient: '$recipient' } 分组，以便根据user 对最后一条消息进行分组。在$lookup 中更改为let: { conversant: "$_id.conversant" }。

试试这个：

 Messages.aggregate([
    {
        $match: {
            $or: [
                { recipientId: req.query.recipientId },
                { creator: mongoose.Types.ObjectId(req.query.recipientId) }
            ]
        }
    },
    {
        $addFields: {
            conversant: {
                $cond: [
                    { $eq: ["$recipientId", req.query.recipientId] },
                    "$recipientId",
                    { $toString: "$creator" }
                ]
            }
        }
    },
    {
        $group: {
            _id: { conversant: "$conversant", recipient: '$recipient' },
            message: { $last: "$message" },
            recipientId: { $last: "$recipientId" },
            creator: { $last: "$creator" },
            messageTrackingId: { $last: "$messageTrackingId" },
            recipient: { $last: "$recipient" },
            creationDate: { $last: "$creationDate" }
        }
    },
    {
        $lookup: {
            from: "users",
            let: { conversant: "$_id.conversant" },
            pipeline: [
                { $match: { $expr: { $eq: ["$_id", "$$conversant"] } } },
                { $project: { instagramName: 1 } }
            ],
            as: "creatorName"
        }
    },
     // this is optional only if you wanted to return latest document irrespective of user.
     { $sort: { creationDate: -1 } }
])