Mongo get grader class in the campus

gistfile1.js

use test

db.grades.aggregate([
{ $unwind: "$scores" }
, { $group: {
    _id: {
      type: "$scores.type"
      , score: "$scores.score"
      , class_id: "$class_id"
    }
  }
}
, { $match: {
    '_id.type': { $ne: 'quiz' }
  }
}
, { $group: {
    _id: "$_id.class_id"
    , avg: { $avg: "$_id.score"}
  }
}
, { $sort: { avg: -1 } }
, { $limit: 1}
]);