Build Applications with Meteor

Let's create another method that will calculate the cart's total price

 On the server:

   cartTotal: function() {    let total = CartCollection.aggregate([        { $project: {"priceByquantity":{ $multiply: [ "$price", "$quantity" ] } }},        { $group: { "_id": "null", "totalPrice": { $sum: "$priceByquantity" } } }        ]);     return total; }

Instead of looping in the items, we can use the MongoDB aggregates. With aggregates, we can group multiple documents, perform calculations, and return a result.

To use aggregates with Meteor, we need to install a package to add support for it. I am using meteorhacks:aggregate, which is available in Atmosphere:

>> meteor add meteorhacks:aggregate

We use $project: to generate the priceByquantity key with a value multiplication ...