MongoDB 将 $lookup 结果添加到数组

Question

我有两个收藏

用户：

{
  { _id: 1, name: 'John' },
  { _id: 2, name: 'Sarah' },
  { _id: 3, name: 'Mike' }
}

服务：

{
  { _id: 1, 
    payment: [
      { uid: 1, paid: true },
      { uid: 2, paid: false }
    ]
  },
  { _id: 2, 
    payment: [
      { uid: 3, paid: true }
    ]
  }
}

我需要这样的结果（来自服务）：

{
  { _id: 1, 
    payment: [
      { uid: 1, paid: true, user: { _id: 1, name: 'John' } },
      { uid: 2, paid: false, user: { _id: 2, name: 'Sarah' } }
    ]
  },
  { _id: 2, 
    payment: [
      { uid: 3, paid: true, user: { _id: 3, name: 'Mike' } }
    ]
  }
}

我可以通过 uid 字段进行 $lookup，但是如何在查找结果中为每个项目添加“付费”字段？我知道这一定很简单……但现在不适合我；）

提前致谢！

Answer 1

db.getCollection('services').aggregate([
    { "$match": {} },
    { "$unwind": '$payment' },
    { "$lookup": {
        "from": "users",
        "localField": "payment.cid",
        "foreignField": "_id",
        "as": "user_data"
    }},
    { "$unwind": '$user_data' },
    { "$addFields": {
        "payment.user.name": "$user_data.name",
    }},
    { "$group": {
        "_id": "$_id",
        "payment": { "$push": "$payment" }
    }}
])