$elemMatch在数组中获取特定值

Question

我有一个名为“考勤”的集合，它有一个数组：

[
  {
    "faculty": "20XX-XXXXX-XX-1",
    "sections": [
      {
        "section": "XXXX 3-1",
        "date": "04-11-2022",
        "attendance": [
          {
            "number": "XXXXX",
            "status": "Present"
          },
          {
            "number": "XXXXX",
            "status": "Present"
          },
          {
            "number": "XXXXX",
            "status": "Present"
          }
        ]
      },
      {
        "section": "XXXX 3-2",
        "date": "04-11-2022",
        "attendance": [
          {
            "number": "XXXXX",
            "status": "Present"
          },
          {
            "number": "XXXXX",
            "status": "Present"
          },
          {
            "number": "XXXXX",
            "status": "Present"
          }
        ]
      }
    ]
  }
]

我一直试图使用$and和$elemMatch查询数组中特定元素的值：

db.attendance.find({$and:[{faculty:"20XX-XXXXX-XX-1"},{sections:{$elemMatch:{section:"XXXX 3-1",date:"04-11-2022"}}}]});

但它仍然印在另一个部分而不是一个。我希望产出如下：

{
    "faculty": "20XX-XXXXX-XX-1",
    "sections": [
      {
        "section": "XXXX 3-1",
        "date": "04-11-2022",
        "attendance": [
          {
            "number": "XXXXX",
            "status": "Present"
          },
          {
            "number": "XXXXX",
            "status": "Present"
          },
          {
            "number": "XXXXX",
            "status": "Present"
          }
        ]
      }

我试着用点表示法，比如：

db.attendance.find({"sections.section":"XXXX 3-1", "sections.date":"04-11-2022});

还是没有运气。我不确定我做的是对还是错。提前感谢！

Answer 1

选项1：/elemMatch->您还需要将$elemMatch添加到查找查询的项目部分，如下所示：

db.collection.find({
 "faculty": "20XX-XXXXX-XX-1",
 sections: {
   $elemMatch: {
    section: "XXXX 3-1",
    date: "04-11-2022"
   }
 }
},
{
 sections: {
   $elemMatch: {
     section: "XXXX 3-1",
     date: "04-11-2022"
   }
 }
})

解释：

查找查询具有以下syntax:db.collection.find({ query }，{ project })，添加项目部分允许您筛选预期的输出。

游乐场备选方案1

选项2：通过聚合/$filter：

  db.collection.aggregate([
  {
  "$addFields": {
   "sections": {
    "$filter": {
      "input": "$sections",
      "as": "s",
      "cond": {
        $and: [
          {
            $eq: [
              "$$s.section",
              "XXXX 3-1"
            ]
          },
          {
            $eq: [
              "$$s.date",
              "04-11-2022"
            ]
          }
        ]
       }
      }
     }
    }
   }
 ])

解释：

将原始区段数组替换为根据所提供的条件过滤数组元素的新区段数组。

游乐场备选方案2