MongoDB aggregation to fetch documents with specific field value?

To fetch documents with a specific field value using MongoDB aggregation, use the aggregate() method with the $match stage to filter documents based on field criteria.

Syntax

db.collection.aggregate([
    { $unwind: "$arrayField" },
    { $match: { "arrayField.fieldName": value } },
    { $project: { _id: 0 } }
]);

Sample Data

db.demo685.insertOne({
    "details": [
        {
            "Name": "Chris",
            "Age": 21
        },
        {
            "Name": "David",
            "Age": 23
        },
        {
            "Name": "Bob",
            "Age": 21
        }
    ]
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5ea54f6fa7e81adc6a0b395b")
}

Display all documents from the collection:

db.demo685.find();

{
    "_id": ObjectId("5ea54f6fa7e81adc6a0b395b"),
    "details": [
        { "Name": "Chris", "Age": 21 },
        { "Name": "David", "Age": 23 },
        { "Name": "Bob", "Age": 21 }
    ]
}

Example: Fetch Documents with Age = 21

db.demo685.aggregate([
    { $unwind: "$details" },
    { $match: { "details.Age": 21 } },
    { $project: { _id: 0 } }
]);

{ "details": { "Name": "Chris", "Age": 21 } }
{ "details": { "Name": "Bob", "Age": 21 } }

How It Works

• $unwind − Deconstructs the array field to output separate documents for each element
• $match − Filters documents where the Age field equals 21
• $project − Excludes the _id field from the output

Conclusion

Use the aggregation pipeline with $unwind and $match stages to filter documents containing array elements with specific field values. This approach effectively extracts matching nested objects from arrays.