I can print out each element of an array by iterating through all values, but can't get a specific element in MongoDB

In MongoDB, you can fetch specific elements from arrays using projection operators like $elemMatch or array indexing, which is more efficient than iterating through all values with forEach().

Syntax

// Using array index
db.collection.find({}, {"arrayField.index": 1});

// Using $elemMatch
db.collection.find({}, {arrayField: {$elemMatch: {field: "value"}}});

Sample Data

db.demo742.insertOne({
    "userDetails": [
        {
            "userName": "Robert",
            "CountryName": "UK"
        },
        {
            "userName": "David", 
            "CountryName": "AUS"
        }
    ]
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5ead790b57bb72a10bcf0677")
}

Method 1: Using Array Index (Get First Element)

db.demo742.find({}, {"userDetails.0": 1});

{
    "_id": ObjectId("5ead790b57bb72a10bcf0677"),
    "userDetails": [
        {
            "userName": "Robert",
            "CountryName": "UK"
        }
    ]
}

Method 2: Using $elemMatch (Get Specific Element)

db.demo742.find({}, {userDetails: {$elemMatch: {CountryName: "AUS"}}});

{
    "_id": ObjectId("5ead790b57bb72a10bcf0677"),
    "userDetails": [
        {
            "userName": "David",
            "CountryName": "AUS"
        }
    ]
}

Method 3: Using forEach() (Original Approach)

var ListOfCountryName = {};
db.demo742.find({}).forEach(function(doc) {
    doc.userDetails.forEach(function(d) {
        ListOfCountryName[d.CountryName] = d.CountryName;
    });
});
printjson(ListOfCountryName);

{
    "UK": "UK",
    "AUS": "AUS"
}

Key Points

• Array indexing is fastest for getting elements by position.
• $elemMatch is ideal for filtering specific array elements by field values.
• forEach() provides full control but is slower for large datasets.

Conclusion

Use array indexing or $elemMatch projection operators to fetch specific array elements efficiently in MongoDB. These methods are more performant than iterating through all values with forEach().