嵌套数组上的猫鼬聚合

Posted 2023-03-11

【中文标题】嵌套数组上的猫鼬聚合

【英文标题】：mongoose aggregate on a nested array

【发布时间】：2021-04-14 18:35:48

【问题描述】：

我有一个包含子数组的架构，并且它的每个元素都引用另一个架构，如下所示：

 _id: "5fed222d806311ec81d6df23"
 someOtherNestedDoc: 
    _id: "abc",
    someOtherField: 10
 ,
 matches: [
   
      _id: "5fed222d806311ec81d6daf3",
      user: "5fed222d806311ec81d6dcf3",
      probability: 10
   ,
   
      _id: "5fed222d806311ec81d6d1f3",
      user: "5fed222d806311ec81d62cf3",
      probability: 20
   ,
 ]

我想做一个 Mongoose 聚合，在其中我查找每个匹配项的用户引用，并且只为它项目 3 个字段，2 个已经存在，第三个是该模式的数组的总和，所以最后，我有这样的事情：

 _id: "5fed222d806311ec81d6df23"
 someOtherNestedDoc: 
    _id: "abc",
    someOtherField: 10
 ,
 matches: [
   
      _id: "5fed222d806311ec81d6daf3",
      user: 
         firstName: "Max",
         lastName: "Mustermann",
         totalExpenses: 100
      ,
      probability: 10
   ,
   
      _id: "5fed222d806311ec81d6d1f3",
      user: 
         firstName: "Herbert",
         lastName: "Mustermann",
         totalExpenses: 200
      ,,
      probability: 20
   ,
 ]

用户看起来像这样：

  _id: "5fed222d806311ec81d6dcf3",
  firstName: "Max",
  lastName: "Mustermann",
  password: "test",
  expenses: [
    
      _id: 1,
     price: 50
    ,
    
      _id: 2,
     price: 50
    ,
   ]



  _id: "5fed222d806311ec81d62cf3",
  firstName: "Herbert",
  lastName: "Mustermann",
  password: "test2",
  expenses: [ 
    
      _id: 3,
     price: 75
    ,
    
      _id: 4,
     price: 125
    ,
   ]

【参考方案1】：

$unwind解构matches数组 $lookup 带有用户集合并在 let 中传递用户 ID， $matchuserId 条件 $project 显示必填字段，得到expenses.price 的总和 $unwind解构user数组 $group by _id 并重构 matches 数组

db.col1.aggregate([
   $unwind: "$matches" ,
  
    "$lookup": 
      "from": "user",
      let:  userId: "$matches.user" ,
      pipeline: [
         $match:  $expr:  $eq: ["$_id", "$$userId"]   ,
        
          $project: 
            _id: 0,
            firstName: 1,
            lastName: 1,
            totalExpenses:  $sum: "$expenses.price" 
          
        
      ],
      "as": "matches.user"
    
  ,
   $unwind: "$matches.user" ,
  
    $group: 
      _id: "$_id",
      matches:  $push: "$matches" 
    
  
])

Playground

【讨论】：

这通常工作得很好，唯一的事情是，如果我在原始文档中除了“匹配”之外还有其他字段，那么这些字段就会丢失。我怎样才能保存这些？我编辑了问题。

你可以使用带有字段名的 $first 运算符看看这个playground