如何使用MGO聚合管道查找符合特定条件的所有嵌入式文档

Question

Lets say I have the following data in a Groups collection in MongoDB

[
    {
        “Group”: {
            “_id”: 1,
            “Requests”: [
                {
                    “_id”:1,
                    “name”:”Request A”
                }.
                {
                    “_id”:2,
                    “name”:”Request B”
                }
            ]       
        }
    },
            {
        “Group”: {
            “_id”: 2,
            “Requests”: [
                {
                    “_id”:3,
                    “name”:”Request C”
                }.
                {
                    “_id”:4,
                    “name”:”Request D”
                }
            ]       
        }
    }

]

Also, lets say I have the following function

func GetRequests(requestIDs []string) (Request[] error){
        //NEED TO IMPLEMENT W/ MGO
}

Is there a way to use the aggregation pipeline (or not if its not needed) to return just a projection of the requests matching requestIDs?

For example

Sample input reflecting requestIds

[1,2,4]

Sample output from mgo aggregation/query

[
  {
    “_id”:1,
    “name”:”Request A”
  },
  {
    “_id”:2,
    “name”:”Request B”
  },
  {
    “_id”:4,
    “name”:”Request D”
  }
]

Answer 1

Try this

db.groups.aggregate([{$unwind : '$Requests'},
                     {$match: {'Requests._id' :{$in: [1,2,4]}}}, 
                     {$project : {_id : '$Requests._id',name:'$Requests.name'}}]);