如何在 MongoDb 中使用 $lookup 及其管道在查找字段中添加 localField

字段中添加 localField"/>

如何在 MongoDb 中使用 $lookup 及其管道在查找字段中添加 localField

我想弄清楚如何使用 $lookup 和管道在

localField

lookup field

所以我有一个

user

"added_at"

 User {
   _id: ObjectId("123456789xx")
   first_name: "Sam",
   last_name: "Jones",
   email: "[email protected]",
   inbox: [
      {
          participant: ObjectId("1XXXXXXXXX),
          added_at: "12:00:00 09/21/2021"
      },
      {
          participant: ObjectId("2XXXXXXXXX),
          added_at: "12:00:00 11/21/2022"
      },
   ]
}

现在我使用 $lookup 来填充

participant

{
   from: "Users",
   localField: "inbox.participant",
   foreignField:"_id",
   as: "participants",
   pipeline:[
      { $project: {first_name:1, last_name:1, _id: 1}}
   ]
}

然后我结束你得到：

{
  _id: ObjectId("123456789xx")
  first_name: "Sam",
  last_name: "Jones",
  email: "[email protected]",
  inbox:...,
  participants: [
     { _id: ObjectId("1xxxxx"), first_name: "John", last_name:"Doe"},
     { _id: ObjectId("2xxxxx"), first_name: "Jack", last_name: "Smith"}
  ]
}

我希望能够在每个参与者中保留

"added_at"

非常感谢您的帮助。

谢谢