Mongo 逐对聚合

Posted 2023-03-29

【中文标题】Mongo 逐对聚合

【英文标题】：Mongo aggregate group by pair

【发布时间】：2021-12-21 05:36:19

【问题描述】：

我有这样的收藏

User	Receiver	IsRead
A	B	false
B	A	false
A	B	false
A	C	false
C	A	false

如何按用户和接收者分组以获得这样的结果

Combined Field	Messages
AB OR BA	3
AC OR CA	2

试过了

$group: 
    _id: $or: [userId: "$recipientId", recipientId: "$userId", userId: "$userId", recipientId: "$recipientId"],
    messages: $sum: $cond: [$eq: ['$isRead', false], 1, 0] // count

【参考方案1】：

您可以将$group 键设置为User 和Receiver 字段的$setUnion。

db.collection.aggregate([
  
    $group: 
      _id: 
        "$setUnion": [
          [
            "$User"
          ],
          [
            "$Receiver"
          ]
        ]
      ,
      "Messages": 
        $sum: 
          "$cond": 
            "if": 
              $not: "$IsRead"
            ,
            "then": 1,
            "else": 0
          
        
      
    
  
])

这是Mongo playground 供您参考。