Retrieve only the queried element in an object array in MongoDB collection?

To retrieve only the matching element from an object array in MongoDB, use the $elemMatch projection operator or the $ positional projection operator. Both return only the first array element that matches the query condition.

Create Sample Data

db.objectArray.insertMany([
    {
        "Persons": [
            {"PersonName": "Adam", "PersonSalary": 25000},
            {"PersonName": "Larry", "PersonSalary": 27000}
        ]
    },
    {
        "Persons": [
            {"PersonName": "David", "PersonSalary": 32000},
            {"PersonName": "Carol", "PersonSalary": 77000}
        ]
    }
]);

Method 1: Using $elemMatch

$elemMatch in the projection filters the array to return only the matching element ?

db.objectArray.find(
    {"Persons.PersonSalary": 25000},
    {_id: 0, Persons: {$elemMatch: {"PersonSalary": 25000}}}
).pretty();

{
    "Persons": [
        {
            "PersonName": "Adam",
            "PersonSalary": 25000
        }
    ]
}

_id: 0 excludes the _id field. $elemMatch returns only the first array element where PersonSalary equals 25000.

Method 2: Using $ Positional Operator

The $ operator projects the first matching array element ?

db.objectArray.find(
    {"Persons.PersonSalary": 25000},
    {_id: 0, "Persons.$": 1}
).pretty();

{
    "Persons": [
        {
            "PersonName": "Adam",
            "PersonSalary": 25000
        }
    ]
}

Comparison

Conclusion

Use $elemMatch projection for complex filtering conditions on array elements. Use the $ positional operator for simpler cases where the query condition already matches the desired element. Both return only the first matching array element, not the entire array.