MongoDB 查找并映射 2 个结果数组

Posted 2023-03-11

【中文标题】MongoDB 查找并映射 2 个结果数组

【英文标题】：MongoDB lookup and map 2 arrays of result

【发布时间】：2021-07-19 18:16:10

【问题描述】：

我在MongoDB聚合管道中查找后有2个数组字段。

第一个

[
    
        "colorId": "60828a1b216b0972da695f2a",
        "name": "Exellent",
        "description": "Great work"
    
]

第二个

[
    
        "_id": "60828a1b216b0972da695f2a",
        "colorName": "Green",
        "hexColorCodes": "#2D9D78",
        "sequence": 1,
        "isActivated": true,
        "created_at": "2021-04-23T08:49:31.729Z",
        "updated_at": "2021-04-23T08:49:31.729Z",
        "__v": 0,
        "isDefault": true
    
]

我想要的结果是

[
  
    "colorId": "60828a1b216b0972da695f2a",
    "name": "Exellent",
    "description": "Great work",
    "colorName": "Green",
    "hexColorCodes": "#2D9D78"
  
]

然后我想将colorName 和hexColorCodes 映射到第一个数组。这是我的聚合管道

db.collection.aggregate([

      $lookup: 
        from: "color_tags",
        localField: "colors.colorId",
        foreignField: "_id",
        as: "tempColors",
      ,
    ,
    
      $addFields: 
        stages3: 
          $map: 
            input: "$colors",
            in: 
              $mergeObjects: [
                "$$this",
                
                  $arrayElemAt: [
                    "$tempColors",
                    
                      $indexOfArray: [
                        "$tempColors._id",
                        "$$this.colors.colorId",
                      ],
                    ,
                  ],
                ,
              ],
            ,
          ,
        ,
      ,
    
])

但结果不是我所期望的。它映射了不正确的 ID。请提出建议。

【参考方案1】：

$map 迭代 first 数组的循环 $filter 迭代 second 数组的循环并将 colorId 与 _id 匹配并返回匹配结果 $arrayElemAt 获取第一个匹配元素 $mergeObjects 将当前对象与 second 数组的返回结果合并

  
    $project: 
      first: 
        $map: 
          input: "$first",
          as: "f",
          in: 
            $mergeObjects: [
              "$$f",
              
                $arrayElemAt: [
                  
                    $filter: 
                      input: "$second",
                      cond:  $eq: ["$$this._id", "$$f.colorId"] 
                    
                  ,
                  0
                ]
              
            ]
          
        
      
    
  

如果您想生成特定字段，请在末尾添加 $project 阶段，

  
    $project: 
      "first.colorId": 1,
      "first.name": 1,
      "first.description": 1,
      "first.colorName": 1,
      "first.hexColorCodes": 1
    
  

Playground