MongoDB聚合推送索引

Posted 2023-03-11

【中文标题】MongoDB聚合推送索引

【英文标题】：Mongodb aggregate push index

【发布时间】：2019-07-22 11:04:55

【问题描述】：

我有以下文件：

  
    _id: "1",
    firstName: "john",
    lastName: "Doe",
    cars: [
      
        "_id": "2",
        "carName": "BMW",
        "carModel": "330",
        "carColor": "silver"
      ,
      
        "_id": "4",
        "carName": "BMW",
        "carModel": "330",
        "carColor": "pink"
      ,
      
        "_id": "5",
        "carName": "Lexus",
        "carModel": "IS300",
        "carColor": "white"
      ,
      
        "_id": "6",
        "carName": "LADA",
        "carModel": "2106",
        "carColor": "blue"
      
    ]
  

使用聚合查询，我从以下文档的 cars 数组返回特定​​对象：

db.collection.aggregate([
  
    $match: 
      firstName: "john"
    
  ,
  
    $unwind: "$cars"
  ,
  
    $match: 
      "cars.carName": 
        "$in": [
          "Lexus",
          "LADA"
        ]
      
    
  ,
  
    $group: 
      "_id": null,
      cars: 
        $push: "$cars"
      
    
  
])

是否也可以获取推送到cars 数组的每个对象的索引？

例如：

[
  
    "_id": null,
    "cars": [
      
        "_id": "5",
        "carColor": "white",
        "carModel": "IS300",
        "carName": "Lexus",
        "index": 2
      ,
      
        "_id": "6",
        "carColor": "blue",
        "carModel": "2106",
        "carName": "LADA",
        "index": 4
      
    ]
  
]

可以测试聚合查询here

【参考方案1】：

您可以尝试以下聚合 (includeArrayIndex)

db.collection.aggregate([
   "$match":  "firstName": "john" ,
   "$unwind":  "path": "$cars", "includeArrayIndex": "index", ,
   "$match":  "cars.carName":  "$in": ["Lexus", "LADA"] ,
   "$addFields":  "cars.index": "$index" ,
   "$group": 
    "_id": null,
    "cars":  "$push": "$cars" 
  
])

Mongoplayground

【讨论】：

是否有其他方法可以在不使用$mergeObjects 的情况下实现这一目标？我有 3.2 版本的 mongoDb，它不支持该属性。

我*更新了我的答案

非常感谢。这个答案对我帮助很大！我被这个索引问题困了几个小时。