node.js - 如何返回从 MongoDb 中的一个数组过滤出来的多个数组

Question

我在 MongoDb 数据库中有一些数据，并使用 NodeJS MongoDb native 驱动程序访问它。

user: {
    _id: ****Example Id****
    name: 'Foo bar',
    examScores: [
        { subject: 'Geography', score: 80, teacher: 'Mr Foo', date: 'somedate'},
        { subject: 'History', score: 57, teacher: 'Mrs Bar', date: 'somedate'},
        { subject: 'Maths', score: 43, teacher: 'Mrs Fizz', date: 'somedate'},
        { subject: 'Geography', score: 43, teacher: 'Mr Buzz', date: 'somedate'},
        { subject: 'Geography', score: 78, teacher: 'Mr Foo', date: 'somedate'},
        { subject: 'History', score: 41, teacher: 'Mr Buzz', date: 'somedate'}
    ]
}

我想检索每个科目的前十名分数/考试。为了简洁起见，我没有在示例中包含超过十次的考试尝试。

类似于:

user: {
    _id: ****Example Id****
    name: 'Foo bar',
    grades: [
        { subject: 'Geography', exams: [ 
            { score: 80, teacher: 'Mr Foo', date: 'somedate' },
            { score: 78, teacher: 'Mr Foo', date: 'somedate' },
            { score: 43, teacher: 'Mr Buzz', date: 'somedate' }
            ]
        },
        { subject: 'History', exams: [
            { score: 57, teacher: 'Mrs Bar', date: 'somedate' },
            { score: 41, teacher: 'Mr Buzz', date: 'somedate'}
            ]
        },
        { subject: 'Maths', exams: [
            { score: 43, teacher: 'Mrs Fizz', date: 'somedate'}
            ]
        }
    ]
}       

Answer 1

尝试这个查询希望它有帮助。我用过$unwind ，然后聚合数据。

db.collection.aggregate([ {$unwind:"$examScores"}, 

{$group:{"_id":"$examScores.subject",name: { $first: "$name" }, exams: { 

$addToSet:{ teacher: '$examScores.teacher' 

,score:'$examScores.score',date:'$examScores.date' } }}},

{$group:{"_id":null,name: { $first: "$name" }, "grades":{$push: 

{"subject":"$_id", "exams":"$exams"}}}},

{$project:{"_id":0,"grades":1,"name":1}} ])

我得到的预期输出是在我的本地计算机上

{
  "name": "Foo bar",
  "grades": [
    {
      "subject": "History",
      "exams": [
        {
          "teacher": "Mr Buzz",
          "score": 41,
          "date": "somedate"
        },
        {
          "teacher": "Mrs Bar",
          "score": 57,
          "date": "somedate"
        }
      ]
    },
    {
      "subject": "Maths",
      "exams": [
        {
          "teacher": "Mrs Fizz",
          "score": 43,
          "date": "somedate"
        }
      ]
    },
    {
      "subject": "Geography",
      "exams": [
        {
          "teacher": "Mr Foo",
          "score": 78,
          "date": "somedate"
        },
        {
          "teacher": "Mr Buzz",
          "score": 43,
          "date": "somedate"
        },
        {
          "teacher": "Mr Foo",
          "score": 80,
          "date": "somedate"
        }
      ]
    }
  ]
}