Question

我预测我的收藏和回应是

{$project: {     
    BusinessCode: {$substrCP : ["$Payload", {$sum : ["$start",15]},{$subtract : [{$subtract : ["$end", "$start"]}, 18]}]}}
}

响应：

{ "_id" : UUID("e3c966cd-cf45-4e42-9a0c-c1d49dcd6c4c"), "BusinessCode" : "8-4-208696-14-1-0-0" }：

现在我想拆分BusinessCode并将第一个char放入其他不存在的字段中。使用此命令我可以这样做：

{$project: {
    BusinessCode:1 ,
     Domain : {$ifNull:[ "$Domain", { $arrayElemAt: [ { $split : ["$BusinessCode", "-"] },0]}]}}
 }

此时我的查询是：

{$project: {     
    BusinessCode: {$substrCP : ["$Payload", {$sum : ["$start",15]},{$subtract : [{$subtract : ["$end", "$start"]}, 18]}]}}
},
{$project: {
    BusinessCode:1 ,
     Domain : {$ifNull:[ "$Domain", { $arrayElemAt: [ { $split : ["$BusinessCode", "-"] },0]}]}}
 }

及其回应：

{
    "_id" : UUID("e3c966cd-cf45-4e42-9a0c-c1d49dcd6c4c"),
    "BusinessCode" : "8-4-208696-14-1-0-0",
    "Domain" : "8"
}

我认为，我有两个独立的项目并不好，但我怎么能将这两个投影合二为一？

Answer 1

试试$let运营商。

{"$replaceRoot":{"newRoot":{
  "$let":{
    "vars":{
      "code":{"$substrCP":["$Payload",{"$sum":["$start",15]},{"$subtract":[{"$subtract":["$end","$start"]},18]}]}
    },
    "in":{
      "BusinessCode":"$$code",
      "Domain":{"$ifNull":["$Domain",{"$arrayElemAt":[{"$split":["$$code","-"]},0]}]}
    }
  }
}}}

Mongodb：在投影时添加字段

1 个答案: