Question

我有一个收藏品，里面有很多文件。例如其中一个文档。

    "_id" : ObjectId("5c018f2c81d68232a4cd3bab"),
    "id" : 1,
    "first_name" : "Nata",
    "last_name" : "Edy",
    "email" : "nedy0@bravesites.com",
    "gender" : "Female",
    "phone" : "473-560-2667",
    "group" : {
            "group_id" : "gr02",
            "form_of_educt" : "daytime",
            "syllabus" : {
                    "titel_of_subj" : "INFO",
                    "subjects" : [
                            {
                                    "sub_id" : 1,
                                    "titel_of_sub" : "Mathematics",
                                    "teacher" : "Ing. Hora",
                                    "mark" : 3
                            },
                            {
                                    "sub_id" : 2,
                                    "titel_of_sub" : "Web Design",
                                    "teacher" : "Ing. Masner",
                                    "mark" : 1
                            },
                            {
                                    "sub_id" : 3,
                                    "titel_of_sub" : "Programming",
                                    "teacher" : "Dr. Gates",
                                    "mark" : 2
                            }
                    ]
            }
    }

我需要从整个收藏集中找到数学主题的平均值 标记。我想我需要使用Aggregation Framework，但我不了解如何将其用于对象数组。

Сan，请帮我。预先谢谢你。

Answer 1

此汇总作业将返回整个集合中的数学分数平均值

db.collection.aggregate([
  {
    $unwind: "$group.syllabus.subjects"
  },
  {
    $match: {
      "group.syllabus.subjects.titel_of_sub": "Mathematics"
    }
  },
  {
    $group: {
      _id: null,
      avg_math_marks: {
        $avg: "$group.syllabus.subjects.mark"
      }
    }
  }
])

MongoDB从对象数组中找到平均值

1 个答案: