连接多个集合，组，对推数组进行排序并重组结果的MongoDB查询

如何解决连接多个集合，组，对推数组进行排序并重组结果的MongoDB查询

MongoDB Playground链接here。以下列出了Data和Desired Result。学生可以一次又一次地参加同一门课程。我希望结果与_id: 1的学生匹配，然后按课程分组，然后按学期排序startDate并仅返回最近的学期。这可能吗？

数据

db={
  registers: [
    {
      _id: 1,student: 1,school: 1,course: 1,semester: 1,grade: 59
    },{
      _id: 2,semester: 2,grade: 99
    },{
      _id: 3,school: 2,course: 2,semester: 3,grade: 100
    }
  ],students: [
    {
      _id: 1,name: "Student1"
    },name: "Student2"
    }
  ],schools: [
    {
      _id: 1,name: "Zefram Cochrane High School"
    },name: "Star Fleet Academy"
    }
  ],courses: [
    {
      _id: 1,name: "Warp Theory"
    },name: "Temporal Mechanics"
    }
  ],semesters: [
    {
      _id: 1,name: "Fall 2320",startDate: ISODate("2320-02-01"),endDate: ISODate("2320-05-31")
    },startDate: ISODate("2320-09-01"),endDate: ISODate("2320-12-31")
    },name: "Spring 2321",startDate: ISODate("2321-02-01"),endDate: ISODate("2321-05-31")
    }
  ]
}

期望结果

[
  {
    "course": {
      "name": "Warp Theory"
    },"grade": 99,"school": {
      "name": "Zefram Cochrane High School"
    },"semester": {
      "endDate": ISODate("2320-12-31T00:00:00Z"),"name": "Fall 2320","startDate": ISODate("2320-09-01T00:00:00Z")
    },"student": {
      "name": "Student1"
    }
  },{
    "course": {
      "name": "Temporal Mechanics"
    },"grade": 100,"school": {
      "name": "Star Fleet Academy"
    },"semester": {
      "endDate": ISODate("2321-05-31T00:00:00Z"),"name": "Spring 2321","startDate": ISODate("2321-02-01T00:00:00Z")
    },"student": {
      "name": "Student1"
    }
  }
]

解决方法

我将仅简要介绍这些更改：

• 过滤最大startDate
• 包含的成绩
• 试图略微改善您要求的格式。 （可以回滚）

输出

[
  {
    "course": "Warp Theory","grade": 99,"school": "Zefram Cochrane High School","semester": {
      "endDate": ISODate("2320-12-31T00:00:00Z"),"startDate": ISODate("2320-09-01T00:00:00Z")
    },"student": "Student1"
  },{
    "course": "Temporal Mechanics","grade": 100,"school": "Star Fleet Academy","semester": {
      "endDate": ISODate("2321-05-31T00:00:00Z"),"startDate": ISODate("2321-02-01T00:00:00Z")
    },"student": "Student1"
  }
]

管道

db.registers.aggregate([
  {
    $match: {
      student: 1
    }
  },{
    $lookup: {
      from: "students",localField: "student",foreignField: "_id",as: "student"
    }
  },{
    $unwind: "$student"
  },{
    $lookup: {
      from: "schools",localField: "school",as: "school"
    }
  },{
    $unwind: "$school"
  },{
    $lookup: {
      from: "courses",localField: "course",as: "course"
    }
  },{
    $unwind: "$course"
  },{
    $lookup: {
      from: "semesters",localField: "semester",as: "semester"
    },},{
    $unwind: "$semester"
  },{
    "$addFields": {
      "semester.grade": "$grade"
    }
  },{
    $group: {
      _id: {
        course: "$course.name",school: "$school.name",student: "$student.name"
      },semester: {
        $push: "$semester"
      },max: {
        $max: "$semester.startDate"
      }
    }
  },{
    $addFields: {
      course: "$_id.course",school: "$_id.school",student: "$_id.student",semester: {
        $filter: {
          input: "$semester",as: "s",cond: {
            $eq: [
              "$$s.startDate","$max"
            ]
          }
        }
      }
    }
  },{
    $addFields: {
      "grade": "$semester.grade"
    }
  },{
    $unset: [
      "max","_id","semester._id","semester.grade","semester.name"
    ]
  },{
    $unwind: "$grade"
  }
])