MongoDb aggregation for filtering list based on ids and mapping this filtered list to another field

In my mongodb I have the data as shown below:

{
  "classes": [
    {
      "classId": "SSC",
      "studentIds": [
        "1"
      ]
    },
    {
      "classId": "HSC",
      "studentIds": [
        "2",
        "3"
      ]
    }
  ],
  "students": [
    {
      "_id": "1",
      "student": {}
    },
    {
      "_id": "2",
      "student": {}
    },
    {
      "_id": "3",
      "student": {}
    }
  ], 
}

And I want an aggregation query such that it returns the data as shown below:

"classes": [
    {
      "classId":"SSC",
      "students": [
        {
          "id": "1",
          "student": {}
	    }
      ]
    },
    {
      "classId":"HSC",
      "students": [
        {
          "id": "2",
          "student": {},
 	    },
        {
          "id": "3",
          "student": {}
 	    }
      ]
    }
  ]

In this I have list of ids. It should filter the students list for that id and take that object and place this object in class array.

I have tried to use mongodb aggregation for this problem. But unfortunately I am not able write query for that. So can we achieve the above scenario using aggregation.

I am using spring boot mongoTemplate.

You can use $map and $filter,

• $map input classes array create students field and do $filter in students array and check condition ids in array or not

db.collection.aggregate([
  {
    $project: {
      classes: {
        $map: {
          input: "$classes",
          as: "c",
          in: {
            classId: "$$c.classId",
            students: {
              $filter: {
                input: "$students",
                cond: { $in: ["$$this._id", "$$c.studentIds"] }
              }
            }
          }
        }
      }
    }
  }
])

Playground