猫鼬在数组中选择具有特定属性的对象

Question

来自“房屋”系列

{
  _id: "0",
  rooms: [
    {
      roomName: "living-room"
      chairs: "6"
    },

    {
      roomName: "kitchen"
      chairs: "0"
    }
  ]
}

我需要找到_id = 0的房子，并且仅选择 来自“客厅”的“椅子”，结果如下：

{
  chairs: 6
}

我想到的是这样的： House.findOne({_id: '0'}).select('rooms.chairs') // but only from {roomName: "living-room"} 如何完成查询？

Answer 1

这个怎么样？

db.houses.aggregate([
   { $match: { _id: "0" } },
   {
      $project: {
         chairs: {
            $filter: {
               input: "$rooms",
               cond: { $eq: ["$$this.roomName", "living-room"] }
            }
         }
      }
   },
   {
      $replaceRoot: {
         newRoot: {
            chairs: { $arrayElemAt: ["$chairs.chairs", 0] }
         }
      }
   },
])

Answer 2

db.house.findOne({"rooms.chairs":"6"},{"rooms.$":1})