MongoDB Multi level $lookup sort not working - mongodb

Question

Multi level $lookup sort not working in aggregation.
Sorting works only for country, state name. Tried applying sorting for cities, but country sort overwrites the city sort.
Query2 is working but i don't want to sort collections inside lookup pipeline.
Is there any way to achieve all level of sorting(country,state,city) in Query1
Query1(Not Working):
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states",
preserveNullAndEmptyArrays: true
}
},
{
$sort: {
'states.name': 1
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$sort: {
'states.cities.name': 1
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
},
{
$sort: {
name: 1
}
}
])
Query2(Working):
Execution time is 8 times higher than Query1.
[
{
$lookup : {
from : 'states',
let: { 'countryId': '$_id' },
pipeline: [
{
$match: {
$expr:
{
$eq: ['$countryId', '$$countryId']
}
}
},
{
$sort : {
name : -1
}
}
],
as : 'states'
}
},
{
$unwind: {
path: '$states',
preserveNullAndEmptyArrays: true
}
},
{
$lookup : {
from : 'cities',
let: { 'stateId': '$states._id' },
pipeline: [
{
$match: {
$expr:
{
$eq: ['$stateId', '$$stateId']
}
}
},
{
$sort : {
name : -1
}
}
],
as : 'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
]

Answer 1

In the newer $lookup syntax you do not need to use $unwind to join nested fields. You can easily use $lookup inside the pipeline to join multiple level.
[
{ "$lookup": {
"from": "states",
"let": { "countryId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": ["$countryId", "$$countryId"] }}},
{ "$lookup": {
"from": "cities",
"let": { "stateId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": ["$stateId", "$$stateId"] }}},
{ "$sort": { "name": -1 }}
],
"as": "cities"
}},
{ "$sort": { "name": -1 }}
],
"as": "states"
}}
]