db={"tracks":[{_id:ObjectId("642d193e1e946b01a7ce86dd"),user:ObjectId("642a9621371ad5002f6b7c30"),name:"Electron",start:ISODate("2023-03-05T06:46:13.000Z"),end:ISODate("2023-03-05T06:46:21.000Z"),},{_id:ObjectId("642d193e1e946b01a7ce86de"),user:ObjectId("643f6ca47712ec0037cf1f65"),name:"Facebook",start:ISODate("2023-03-05T04:30:13.000Z"),end:ISODate("2023-03-05T04:45:21.000Z"),},{_id:ObjectId("642d19661e946b01a7ce86ec"),user:ObjectId("642a9621371ad5002f6b7c30"),name:"Skype",start:ISODate("2023-03-05T01:15:13.000Z"),end:ISODate("2023-03-05T02:18:21.000Z"),},{_id:ObjectId("642d19ac1e946b01a7ce8706"),user:ObjectId("643f6ca47712ec0037cf1f65"),name:"Vim",start:ISODate("2023-03-05T08:11:13.000Z"),end:ISODate("2023-03-05T08:31:21.000Z"),}],"users":[{_id:ObjectId("642a9621371ad5002f6b7c30"),name:"User 1",email:"user1@example.com",password:"xxxxxxxx",},{_id:ObjectId("643f6ca47712ec0037cf1f65"),name:"User 2",email:"user2@example.com",password:"xxxxxxxx",}]}

db.tracks.aggregate([{"$addFields":{"userId":{"$toString":"$_id"}}},{"$group":{"_id":"$user","name":{"$last":"$name"},"start":{"$last":"$start"},}},{"$lookup":{"from":"users","localField":"_id","foreignField":"_id","as":"userDetail"}},{"$sort":{"start":-1}},{"$unset":["userDetail.password"]}])