Get only matched array object along with parent fields

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
    }
);

score 0 · Accepted Answer · answered Oct 16 '22 at 14:16

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.

Get only matched array object along with parent fields

1 Answers1