如何分组并获取每个分组中的top N以及mongoDB中top N的其他字段

db.orders.aggregate([
  { $group: { _id: "$category", orders: { $push: "$$ROOT" } } }
])

db.orders.aggregate([
  { $group: { _id: "$category", orders: { $push: "$$ROOT" } } },
  { $unwind: "$orders" },
  { $sort: { "orders.amount": -1 } }
])

db.orders.aggregate([
  { $group: { _id: "$category", orders: { $push: "$$ROOT" } } },
  { $unwind: "$orders" },
  { $sort: { "orders.amount": -1 } },
  { $group: { _id: "$_id", topOrders: { $push: "$orders" } } },
  { $project: { _id: 0, category: "$_id", topOrders: { $slice: ["$topOrders", 3] } } }
])