Mongodb 获取聚合框架中的最后一个组合

Question

有一组消息：

{
  "date": NumberLong(1421134514),
  "sender": "53172480f9cd0e682840b9f7",
  "recipient": "52f37fbaf9cd0e02773c97b1",
  "isRead": false,
  "_id": "54b4cab2f6a48ce34f8b5a75",
  "text": "Hello!"
},
{
  "date": NumberLong(1421135561),
  "sender": "53172480f9cd0e682840b9f7",
  "recipient": "52f37fbaf9cd0e02773c97b1",
  "isRead": false,
  "_id": "54b4cec9f6a48ce34f8b6429",
  "text": "Hello 2!"
},
{
  "date": NumberLong(1421135618),
  "sender": "53072122f9cd0ee76306dc5a",
  "recipient": "52f37fbaf9cd0e02773c97b1",
  "isRead": false,
  "_id": "54b4cf02f6a48ce54f8b62f9",
  "text": "Hello 3!"
},
{
  "date": NumberLong(1421136457),
  "sender": "52f37fbaf9cd0e02773c97b1",
  "recipient": "52ea178ff9cd0e9f24d776b4",
  "isRead": false,
  "_id": "54b4d249f6a48ce54f8b6b9f"
  "text": "Hello 4!"
}

需要选择后面的对话，当前用户要么是发送者，要么是接收者。

例如，对于 ID = '52f37fbaf9cd0e02773c97b1' 的用户，应获得 3 条记录。

原来构建了两个单独的查询：

$result = \DB::$connection->message->aggregate(array(
    array('$match' => array('sender' => \Core::getModule('users')->user->_id)),
    array('$group' => array('_id' => '$recipient')),
));

$result2 = \DB::$connection->message->aggregate(array(
    array('$match' => array('recipient' => \Core::getModule('users')->user->_id)), 
    array('$group' => array('_id' => '$sender')),
));

是否可以以某种方式将这两个查询合并为一个并按日期对记录进行排序？

Answer 1

这里您需要的是为 "sender and recipient" 的每个组合生成的 "unique key" 值。如果您想定期执行此操作，那么我建议将值存储在文档中。但这是您可以使用聚合框架摆脱问题的一种方式：

 db.messages.aggregate([
    { "$project": {
       "combined": { "$map": {
           "input": { "$literal": ["A","B"] },
           "as": "bin",
           "in": { "$cond": [ 
               { "$eq": [ "$$bin", "A" ] },
               "$sender",
               "$recipient"
           ]}
       }},
       "doc": "$$ROOT"
    }},
    { "$unwind": "$combined" },
    { "$sort": { "_id": 1, "combined": 1, "doc.date": -1 } },
    { "$group": {
        "_id": "$_id",
        "combined": { "$push": "$combined" },
        "doc": { "$first": "$doc" }
    }},
    { "$group": {
        "_id": "$combined",
        "doc": { "$first": "$doc" }
    }}
])

这将您的示例缩小到 "unique" 3 种组合 "sender / recipient" 和 returns "pair" 之间对话的最后一个文档：

{
    "_id" : [
            "52f37fbaf9cd0e02773c97b1",
            "53172480f9cd0e682840b9f7"
    ],
    "doc" : {
            "_id" : "54b4cec9f6a48ce34f8b6429",
            "date" : NumberLong(1421135561),
            "sender" : "53172480f9cd0e682840b9f7",
            "recipient" : "52f37fbaf9cd0e02773c97b1",
            "isRead" : false,
            "text" : "Hello 2!"
    }
}
{
    "_id" : [
            "52f37fbaf9cd0e02773c97b1",
            "53072122f9cd0ee76306dc5a"
    ],
    "doc" : {
            "_id" : "54b4cf02f6a48ce54f8b62f9",
            "date" : NumberLong(1421135618),
            "sender" : "53072122f9cd0ee76306dc5a",
            "recipient" : "52f37fbaf9cd0e02773c97b1",
            "isRead" : false,
            "text" : "Hello 3!"
    }
}
{
    "_id" : [
            "52ea178ff9cd0e9f24d776b4",
            "52f37fbaf9cd0e02773c97b1"
    ],
    "doc" : {
            "_id" : "54b4d249f6a48ce54f8b6b9f",
            "date" : NumberLong(1421136457),
            "sender" : "52f37fbaf9cd0e02773c97b1",
            "recipient" : "52ea178ff9cd0e9f24d776b4",
            "isRead" : false,
            "text" : "Hello 4!"
    }
}

Mongodb 获取聚合框架中的最后一个组合

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