Perform Group in MongoDB and sum the price record of documents

To sum price records across all documents in MongoDB, use the $group stage in an aggregation pipeline with the $sum operator. Set _id: null to group all documents together.

Syntax

db.collection.aggregate([
    {
        $group: {
            _id: null,
            totalFieldName: { $sum: "$fieldName" }
        }
    }
]);

Sample Data

db.demo527.insertMany([
    { "Price": 45.5 },
    { "Price": 55.5 },
    { "Price": 100.4 },
    { "Price": 200.6 }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e8aff2fef4dcbee04fbbbdc"),
        ObjectId("5e8aff34ef4dcbee04fbbbdd"),
        ObjectId("5e8aff39ef4dcbee04fbbbde"),
        ObjectId("5e8aff40ef4dcbee04fbbbdf")
    ]
}

Display Sample Data

db.demo527.find();

{ "_id": ObjectId("5e8aff2fef4dcbee04fbbbdc"), "Price": 45.5 }
{ "_id": ObjectId("5e8aff34ef4dcbee04fbbbdd"), "Price": 55.5 }
{ "_id": ObjectId("5e8aff39ef4dcbee04fbbbde"), "Price": 100.4 }
{ "_id": ObjectId("5e8aff40ef4dcbee04fbbbdf"), "Price": 200.6 }

Example: Sum All Price Records

db.demo527.aggregate([
    {
        $group: {
            _id: null,
            totalPrice: { $sum: "$Price" }
        }
    }
]);

{ "_id": null, "totalPrice": 402 }

Key Points

• _id: null groups all documents into a single result.
• $sum: "$Price" adds up values from the Price field across all documents.
• The result contains the calculated total in the specified field name.

Conclusion

Use $group with $sum in MongoDB aggregation to calculate totals across document collections. Setting _id: null ensures all documents are grouped together for a single sum result.