聚合比较mongodb中的两个数组？

如何解决聚合比较mongodb中的两个数组？

[
  {
    "dayCount": 3,"dayRange": [
      "2021-05-27","2021-05-28","2021-05-29","2021-05-30","2021-05-31","2021-06-01","2021-06-02"
    ],"totalUserCount": 4,"userCountPerDay": [
      {
        "createdAt": "2021-05-28","userCount": 2
      },{
        "createdAt": "2021-06-02","userCount": 1
      },{
        "createdAt": "2021-06-01","userCount": 1
      }
    ]
  }
]

这是按日期划分的用户访问量。
我需要比较“dayRange”和“userCountPerDay.createdAt”

对于“userCountPerDay.createdAt”中不存在的日期，将“userCount”设置为0

我想使用 mongo 聚合来跟踪结果
请帮帮我。

[
  {
    "dayCount": 3,"userCountPerDay": [
      {
        "createdAt": "2021-05-27","userCount": 0
      },{
        "createdAt": "2021-05-28",{
        "createdAt": "2021-05-29",{
        "createdAt": "2021-05-30",{
        "createdAt": "2021-05-31","userCount": 1
      }
    ]
  }
]

谢谢

解决方法

$project 显示必填字段
$map 迭代 dayRange 数组的循环
$cond 检查当前日期是否在 userCountPerDay.createdAt 数组中的条件，
- 是的，$indexOfArray 用于在 userCountPerDay 数组中获取数组索引或当前日期，$arrayElemAt 从返回的索引中获取元素/对象
- 不，返回 createdAt 和 userCount 字段

db.collection.aggregate([
  {
    $project: {
      dayCount: 1,totalUserCount: 1,userCountPerDay: {
        $map: {
          input: "$dayRange",in: {
            $cond: [
              { $in: ["$$this","$userCountPerDay.createdAt"] },{
                $arrayElemAt: [
                  "$userCountPerDay",{ $indexOfArray: ["$userCountPerDay.createdAt","$$this"] }
                ]
              },{
                createdAt: "$$this",userCount: 0
              }
            ]
          }
        }
      }
    }
  }
])

Playground