Fetch records from a subdocument array wherein id begins from 234 in MongoDB

To fetch records from a subdocument array where id begins with specific digits like "234", use MongoDB's aggregation pipeline with $unwind, $match, and $regex operators. The $unwind deconstructs the array, $regex filters by pattern, and $group with $push reconstructs matching elements.

Syntax

db.collection.aggregate([
    { $match: { "_id": documentId } },
    { $unwind: "$arrayField" },
    { $match: { "arrayField.id": { $regex: /^pattern/ } } },
    { $group: { _id: "$_id", "result": { $push: "$arrayField" } } }
]);

Sample Data

db.demo556.insertOne({
    _id: 101,
    details: [
        { id: "234336", Name: "Chris" },
        { id: "123456", Name: "Bob" },
        { id: "234987", Name: "Carol" },
        { id: "989768", Name: "David" },
        { id: "234888", Name: "Sam" },
        { id: "847656", Name: "John" }
    ]
});

{ "acknowledged": true, "insertedId": 101 }

Example: Fetch Records with IDs Beginning "234"

Use aggregation pipeline to filter subdocuments where id starts with "234" ?

db.demo556.aggregate([
    { $match: { "_id": 101 } },
    { $unwind: "$details" },
    { $match: { "details.id": { $regex: /^234/ } } },
    { $group: { _id: "$_id", "Detail": { $push: "$details" } } }
]);

{
    "_id": 101,
    "Detail": [
        { "id": "234336", "Name": "Chris" },
        { "id": "234987", "Name": "Carol" },
        { "id": "234888", "Name": "Sam" }
    ]
}

How It Works

• $match: { "_id": 101 } − Filters the specific document
• $unwind: "$details" − Deconstructs the details array into separate documents
• $match: { "details.id": { $regex: /^234/ } } − Filters elements where id starts with "234"
• $group with $push − Reconstructs matching elements into a new array

Conclusion

Use MongoDB aggregation pipeline with $unwind, $regex, and $group to filter subdocument arrays by pattern matching. The $regex: /^234/ pattern efficiently matches IDs beginning with "234".