Get only matched array object along with parent fields - mongodb

Question

I also checked the following question and tried various other things but
couldn't get it working
Retrieve only the queried element in an object array in MongoDB collection
I have the following document sample
{
_id: ObjectId("634b08f7eb5cb6af473e3ab2"),
name: 'India',
iso_code: 'IN',
states: [
{
name: 'Karnataka',
cities: [
{
name: 'Hubli Tabibland',
pincode: 580020,
location: { type: 'point', coordinates: [Array] }
},
{
name: 'Hubli Vinobanagar',
pincode: 580020,
location: { type: 'point', coordinates: [Array] }
},
{
name: 'Hubli Bengeri',
pincode: 580023,
location: { type: 'point', coordinates: [Array] }
},
{
name: 'Kusugal',
pincode: 580023,
location: { type: 'point', coordinates: [Array] }
}
]
}
]
}
I need only the following
{
_id: ObjectId("634b08f7eb5cb6af473e3ab2"),
name: 'India',
iso_code: 'IN',
states: [
{
name: 'Karnataka',
cities: [
{
name: 'Kusugal',
pincode: 580023,
location: { type: 'point', coordinates: [Array] }
}
]
}
]
}
Following is the query that I have tried so far but it returns all the cities
db.countries.find(
{
'states.cities': {
$elemMatch: {
'name' : 'Kusugal'
}
}
},
{
'_id': 1,
'name': 1,
'states.name': 1,
'states.cities.$' : 1
}
);

Answer 1

I was able to achieve it with the help of aggregation.
db.countries.aggregate([
{ $match: { "states.cities.name": /Kusugal/ } },
{ $unwind: "$states" },
{ $unwind: "$states.cities" },
{ $match: { "states.cities.name": /Kusugal/ } }
]);
1st line $match will query the records with cities with only Kusugal
2nd & 3rd line $unwind will create a separate specific collection of documents from the filtered records
3rd line $match will filter these records again based on the condition
In simple aggregation processes commands and sends to next command and returns as an single result.