聚集猫鼬$总和，其中

Question

我有查询是这样的：

{"$match": {$or: [{"to": system.mongoose.Types.ObjectId(userId)}, {"from": system.mongoose.Types.ObjectId(userId)}]}}, 
     {"$sort": {"createDate": -1}}, 
     { 
      "$group": { 
       "_id": "$conversationId", 
       "from": {"$first": "$from"}, 
       "to": {"$first": "$to"}, 
       "content": {"$first": "$content"}, 
       "createDate": {"$first": "$createDate"}, 
       "unreaded": {"$sum": 1} 
      } 

     }, 

我不需要编辑主$match我只需要得到unreaded消息的总和，

我需要的是这样的："unreaded": {"$sum": 1, {$match: {unreaded: true}}}

任何解决方案？

Answer 1

使用$cond

"unreaded": {"$sum": {$cond: {if: "$unreaded", then: 1, else: 0} }} 

文档：
https://docs.mongodb.com/manual/reference/operator/aggregation/cond/