db={"user":[{"_id":"6321ac3d14a57c2716f7f4a0","name":"David","city":"63218ce557336b03540c9ce9","country":"632185bbe499d5505cafdcbc","createdAt":"2022-09-14T10:26:05.000Z","__v":0}],"city":[{"_id":"63218ce557336b03540c9ce9","cityName":"New York","__v":0}],"country":[{"_id":"632185bbe499d5505cafdcbc","countryName":"USA","__v":0}]}

db.user.aggregate([{"$match":{_id:"6321ac3d14a57c2716f7f4a0"}},{"$lookup":{"from":"city","localField":"city","foreignField":"_id","as":"city"}},{"$lookup":{"from":"country","localField":"country","foreignField":"_id","as":"country"}},{"$addFields":{"country":{"$arrayElemAt":["$country",0]},"city":{"$arrayElemAt":["$city",0]}}},{"$addFields":{"countryName":"$country.countryName","cityName":"$city.cityName"}},{"$unset":["country","city"]}])