How to get the matching document inside an array in MongoDB?

To get the matching document inside an array in MongoDB, use the $elemMatch operator. This operator matches documents that contain an array field with at least one element that matches all the specified query criteria.

Syntax

db.collection.find({
    "arrayField": {
        $elemMatch: {
            "field1": "value1",
            "field2": "value2"
        }
    }
});

Sample Data

db.getMatchingDocumentDemo.insertMany([
    {
        _id: 1,
        "UserDetails": [
            {
                "UserName": "John",
                "UserAge": 23
            }
        ]
    },
    {
        _id: 2,
        "UserDetails": [
            {
                "UserName": "Larry",
                "UserAge": 24
            }
        ]
    }
]);

{
    "acknowledged": true,
    "insertedIds": {
        "0": 1,
        "1": 2
    }
}

Display all documents to verify the data ?

db.getMatchingDocumentDemo.find().pretty();

{
    "_id": 1,
    "UserDetails": [
        {
            "UserName": "John",
            "UserAge": 23
        }
    ]
}
{
    "_id": 2,
    "UserDetails": [
        {
            "UserName": "Larry",
            "UserAge": 24
        }
    ]
}

Example: Find Document with Matching Array Element

Find documents where UserDetails array contains an element with UserAge equal to 24 ?

db.getMatchingDocumentDemo.find({
    UserDetails: {
        $elemMatch: {
            UserAge: 24
        }
    }
});

{
    "_id": 2,
    "UserDetails": [
        {
            "UserName": "Larry",
            "UserAge": 24
        }
    ]
}

Key Points

• $elemMatch returns the entire document when at least one array element matches all criteria.
• Use $elemMatch when you need to match multiple conditions within the same array element.
• Without $elemMatch, MongoDB would match conditions across different array elements.

Conclusion

The $elemMatch operator effectively finds documents containing array elements that match specific criteria. It ensures all conditions are satisfied by the same array element, making it essential for precise array queries.