How to sum all amount paid by users - node.js

Question

I am finding it defficult to add up all amount paid by customers that ordered items
Order Schema
const orderschema = new Mongoose.Schema({
created: { type: Date, default: Date.now() },
amount: { type: Number, default: 0 }
User: [{ type: Mongoose.Schema.ObjectId, ref: 'Users'}]
...
})
Route
Get('/total-amount', total-amount)
Controller
Exports.total-amount = () => {
Order.find()...
}
I don't know what to add here to get the total amount made by all customers.
Using NodeJS and MongoDB.
Thank you for you help

Answer 1

You can use $sum in an aggregation stage like this:
First $group all (without _id is to group all values)
Then create field total which is the sum of al amount.
And an optional stage, $project to output only total field.
db.order.aggregate({
"$group": {
"_id": null,
"total": {
"$sum": "$amount"
}
}
},
{
"$project": {
"_id": 0
}
})
Example here
To add into a controller using nodeJS and Mongoose you can use something like this piece of code:
Exports.total - amount = (req, res) => {
Order.aggregate({
"$group": {
"_id": null,
"total": {
"$sum": "$amount"
}
}
}, {
"$project": {
"_id": 0
}
}).then(response => {
res.status(200).send(response)
}).catch(e => res.status(400).send())
}
Note hoy the operation is done using your mongoose model (in this case Order). You are calling aggregate method in the same way you call find method for example: Instead of doing
yourModel.find()
Is
yourModel.aggregate()
And the response will be:
[
{
"total": 6
}
]
So even you can update your controller to add a if/else block like this:
if(response[0].total)
res.status(200).send(response[0].total)
else
res.status(404).send()