Question

我有一个包含以下值的文档的集合

{
 "_id": ObjectID("XXXXXX"),
 "more details" :more details
 "attendance": [
    {
        "date": ISODate("2015-08-11T18:30:00.000Z"),
        "students": [
            {
                "studentId": ObjectID("YYYYYY"),
                "entryTime": ISODate("1970-01-01T05:41:00.000Z"),
                "exitTime": ISODate("1970-01-01T05:41:00.000Z"),
                "attendanceStatus": "Present"
            },
            {
                "studentId": ObjectID("ZZZZZZ"),
                "entryTime": ISODate("1970-01-01T06:42:00.000Z"),
                "exitTime": ISODate("1970-01-01T06:42:00.000Z"),
                "attendanceStatus": "Present"
            }
        ]
    },
    {
        "date": ISODate("2015-08-12T18:30:00.000Z"),
        "students": [
            {
                "studentId": ObjectID("XXXXX"),
                "entryTime": ISODate("1970-01-01T05:41:00.000Z"),
                "exitTime": ISODate("1970-01-01T06:42:00.000Z"),
                "attendanceStatus": "Present"
            },
            {
                "studentId": ObjectID("YYYYY"),
                "entryTime": ISODate("1970-01-01T05:41:00.000Z"),
                "exitTime": ISODate("1970-01-01T06:42:00.000Z"),
                "attendanceStatus": "Absent"
            }
        ]
    }
  ]
}

我想知道学生在场的天数以及他缺席的天数。但我不断得到输出未定义。

var pipeline = [
            {
                "$match": {_id: mongoose.Types.ObjectId(batchId)}
            },
            {
                "$project": {attendance: '$attendance.students'}
            },
            {
                "$group": {
                    "studentId": "$studentId"
                    ,
                    "Present": {
                        "$sum": {
                            "$cond": [{"$eq": ["attendanceStatus", "Present"]}, 1, 0]
                        }
                    },
                    "Absent": {
                        "$sum": {
                            "$cond": [{"$eq": ["attendanceStatus", "Absent"]}, 1, 0]
                        }
                    }
                }
            }
        ];

无法弄清楚我错过了什么

Answer 1

请尝试此管道

var pipeline = [{$unwind: '$attendance'}, 
                {$unwind: '$attendance.students'}, 
                {$group: {
                    _id: '$attendance.students.studentId', 
                    "Present": {
                        "$sum": {
                            "$cond": [
                                 {"$eq": ["$attendance.students.attendanceStatus", "Present"]},
                                  1, 
                                  0]
                        }
                     },
                     "Absent": {
                        "$sum": {
                            "$cond": [
                                 {"$eq": ["$attendance.students.attendanceStatus", "Absent"]},
                                   1,
                                   0]
                        }
                    }}}]

用于计算出勤率的mongodb聚合

1 个答案: