Does aggregation query with $match works in MongoDB?

Yes, the $match operator works perfectly in MongoDB aggregation queries. It filters documents in the aggregation pipeline, similar to the find() method's query criteria, but as the first stage of data processing.

Syntax

db.collection.aggregate([
    { $match: { "field": "value" } },
    // Additional pipeline stages...
]);

Sample Data

db.demo358.insertMany([
    { "ClientId": 101, "ClientName": "Chris", "ClientAge": 34 },
    { "ClientId": 102, "ClientName": "David", "ClientAge": 32 },
    { "ClientId": 103, "ClientName": "David", "ClientAge": 35 },
    { "ClientId": 104, "ClientName": "Bob", "ClientAge": 31 },
    { "ClientId": 105, "ClientName": "Chris", "ClientAge": 36 }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e5692c0f8647eb59e5620cb"),
        ObjectId("5e5692caf8647eb59e5620cc"),
        ObjectId("5e5692d2f8647eb59e5620cd"),
        ObjectId("5e5692ddf8647eb59e5620ce"),
        ObjectId("5e5692e7f8647eb59e5620cf")
    ]
}

Display All Documents

db.demo358.find();

{ "_id": ObjectId("5e5692c0f8647eb59e5620cb"), "ClientId": 101, "ClientName": "Chris", "ClientAge": 34 }
{ "_id": ObjectId("5e5692caf8647eb59e5620cc"), "ClientId": 102, "ClientName": "David", "ClientAge": 32 }
{ "_id": ObjectId("5e5692d2f8647eb59e5620cd"), "ClientId": 103, "ClientName": "David", "ClientAge": 35 }
{ "_id": ObjectId("5e5692ddf8647eb59e5620ce"), "ClientId": 104, "ClientName": "Bob", "ClientAge": 31 }
{ "_id": ObjectId("5e5692e7f8647eb59e5620cf"), "ClientId": 105, "ClientName": "Chris", "ClientAge": 36 }

Example: Using $match with $count

Count all clients named "David" using $match and $count ?

db.demo358.aggregate([
    { $match: { "ClientName": "David" } },
    { $count: "ClientName" }
]);

{ "ClientName": 2 }

Key Points

• $match should typically be the first stage in the pipeline to reduce data early
• It uses the same query syntax as find() method
• Can be combined with other aggregation operators like $count, $group, etc.

Conclusion

The $match operator is essential for filtering documents in MongoDB aggregation pipelines. It works efficiently when placed early in the pipeline and supports all MongoDB query operators.