尝试此查询，希望对您有所帮助。我使用过$unwind，然后汇总了数据。

db.collection.aggregate([ {$unwind:"$examScores"},{$group:{"_id":"$examScores.subject",name: { $first: "$name" },exams: { 

$addToSet:{ teacher: '$examScores.teacher',score:'$examScores.score',date:'$examScores.date' } }}},{$group:{"_id":null,"grades":{$push: 

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

我得到的预期输出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,{
      "subject": "Geography","exams": [
        {
          "teacher": "Mr Foo","score": 78,{
          "teacher": "Mr Buzz",{
          "teacher": "Mr Foo","score": 80,"date": "somedate"
        }
      ]
    }
  ]
}

请尝试以下查询：

1. 展开examScores数组
2. 基于主题和分数的降序排序集合，因为 您需要按照分数的降序排列每个主题的结果。
3. 基于主题分组结果

4. 由于只需要列出每个主题的前10个最高分 您可以使用$Slice操作将分数限制在前10 每个主题。

   db.collection.aggregate([ 
   
                  { $unwind : "$examScores" },{ $sort : 
                          { "examScores.subject" : 1,"examScores.score" : -1
                          }
                  },{ $group : { 
                             "_id" : "$examScores.subject","name" : { $first: "$name" },"examsAll" : { 
                                    $addToSet : { 
                                           teacher: '$examScores.teacher',score : '$examScores.score',date : '$examScores.date' 
                                                } 
                                          }
                               }
                  },{ $project : { 
                                "_id" : 1,"name" : 1,"exams" : { $slice: [ "$examsAll",10 ] } 
                               }
                  },{ $group : { "_id" : null,"name" :  { $first: "$name" },"grades" : { $push: 
                                                { "subject" : "$_id","exams" : "$exams" 
                                                }
                                          }
                              }
                  },{ $project : { "_id" : 0,"grades" : 1,"name" : 1
                               }
                  } 
        ]);