如何在 Mongodb 的 map 函数中使用 match

Question

我是 Mongodb 的初学者，我想执行以下查询来查找每个员工的任务总数，任务进度为“工作”。

db.employees.aggregate([
  {
    "$lookup": {
      "from": "assignment",
      "localField": "empno",
      "foreignField": "emp_no",
      "as": "assignments"
    }
  },
  {
    $project: {
      points: {
        $sum: {
          $map: {
            input: "$assignments",
            in: { $match:{$Sthis.progress:"Working"}}
          }
        }
      },
      empno: 1
    }
  }
])

当我执行此查询时，我收到错误“无效的 $project:: 由:: Unrecognized expression '$match' 引起”。我该如何解决这个问题？

Answer 1

将过滤器添加到地图的输入并在过滤器中设置条件

db.employees.aggregate([
  {
    "$lookup": {
      "from": "assignment",
      "localField": "empno",
      "foreignField": "emp_no",
      "as": "assignments"
    }
  },
  {
    $project: {
      points: {
        $sum: {
          $map: {
            input:{"$filter":
            { "input": "$assignments", "as": "z", "cond": {$eq:["$$z.progress","Working"]} } },
            as :"s",
            in: "$$s"
          }
        }
      },
      empno: 1
    }
  
    
  }
])