Concat int和字符串数组字段位于不同的数组中 [英] Concat int and string array fields which are in different arrays

问题描述

{ 
   "no" : "2020921008981",  
   "date" : ISODate("2020-04-01T05:19:02.263+0000"), 
   "sale" : { 
   "soldItems" : [
       {
         "itemId" : "5b55ac7f0550de00210a3b24", 
         "qty" : NumberInt(1), 
       },
       {
         "itemId" : "5b55ac7f0550de00210a3b25", 
         "qty" : NumberInt(2), 
       }
     ],
  "items" : [
       {
         "_id" : ObjectId("5b55ac7f0550de00210a3b24"),
         unit :"KG"
       },
       {
         "_id" : ObjectId("5b55ac7f0550de00210a3b25"),
         unit :"ML"
       }

     ]
   }
 }

所需的输出:

{
 "no" : "2020921008981",
 "sale" : {}
 "qtyList" : "1 KG \n 2 ML"
}

为了构建itemQtyList输出字段，应使用来自不同数组的两个字段(字符串和整数).找不到执行此操作的任何参考.任何想法将不胜感激.

In order to build itemQtyList output field, two fields from different arrays (string and int) should be used. Couldn't find any reference for doing that. Any idea would be appreciated.

推荐答案

您可以在下面的聚合中使用

You can use below aggregation

db.collection.aggregate([
  { "$project": {
    "itemQtyList": {
      "$reduce": {
        "input": { "$range": [0, { "$size": "$sale.soldItems" }] },
        "initialValue": "",
        "in": {
          "$concat": [
            "$$value",
            { "$cond": [{ "$eq": ["$$this", 0] }, "", " \n "] },
            { "$toString": {
              "$arrayElemAt": [
                "$sale.soldItems.qty",
                "$$this"
              ]
            }},
            " ",
            { "$arrayElemAt": ["$sale.items.unit", "$$this"] }
          ]
        }
      }
    }
  }}
])

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