Calculate transaction items total's and transaction item with mongoose query - node.js

Question

In mongoose, I have a collection for transactions. Each transaction has a list of Items Something like this:
var transactionItemSchema = new mongoose.Schema({
productId: String,
quantity: Number,
price: Number
});
var transactionSchema = new mongoose.Schema({
details: String,
items: [transactionItemSchema ],
}, {
timestamps: true
});
I need to calculate each item total's value by multiplying price * quantity and rounding 2 decimals, but also I need to get the transaction total by summing all item total's in a transaction. So for example if I have this transactions in mongo:
[{
details: 'First Transaction',
items: [{
price: 5.2,
quantity: 2
}, {
price: 4,
quantity: 3
}]
}, {
details: 'First Transaction',
items: [{
price: 0.333,
quantity: 3
}]
}]
return something like this when pulling transactions:
[{
total: 22.40,
details: 'First Transaction',
items: [{
price: 5.2,
quantity: 2,
total: 10.40
}, {
price: 4,
quantity: 3,
total: 12.00
}]
}, {
total: 1.00,
details: 'Second Transaction',
items: [{
price: 0.333,
quantity: 3,
total: 1.00
}]
}]
Is there a way we can achieve this with some aggregations with mongoose?

Answer 1

You want $map and $multiply here.
Assuming the model is calls Transaction:
Transaction.aggregate([
{ "$addFields": {
"items": {
"$map": {
"input": "$items",
"in": {
"$mergeObjects": [
"$$this",
{ "total": { "$round": [{ "$multiply": [ "$$this.price", "$$this.quantity" ] }, 2] } }
]
}
}
}
}}
])
Or without $mergeObjects:
Transaction.aggregate([
{ "$addFields": {
"total": {
"$sum": {
"$map": {
"input": "$items",
"in": {
"$round": [{ "$multiply": [ "$$this.price", "$$this.quantity" ] }, 2]
}
}
}
},
"items": {
"$map": {
"input": "$items",
"in": {
"price": "$$this.price",
"quantity": "$$this.quantity",
"total": { "$round": [{ "$multiply": [ "$$this.price", "$$this.quantity" ] }, 2] }
}
}
}
}}
])
The $map operator is essentially used for array transforms, in which you provide an array of input and an expression to apply to each array element which defines the object output for each element. Here $multiply is applied with the two arguments to "multiply" for a result.
The $mergeObjects is optionally used as a way to take the existing object properties for each element ( price and quantity ) and include them in the output object. The alternative is to manually specify the properties in the output objects for each element, just as shown.
Of course for the document total the same is essentially supplied, but just returning a single value and feeding that to the $sum operator in order to "total" the results
All of that said, there's nothing wrong with simply manipulating the result post return from the server:
let results = await Transaction.find().lean();
// Then manipulate the items arrays
results = results.map(r =>
({
...r,
total: r.items.reduce((o, i) =>
o + parseFloat((i.price * i.quantity).toFixed(2)), 0),
items: r.items.map(i =>
({ ...i, total: parseFloat((i.price * i.quantity).toFixed(2)) })
)
})
);
Simply note the use of lean() here, which returns plain JavaScript objects rather than Mongoose Documents and thus allows you to manipulate the structure of the returned results.
Here's a full listing of both approaches:
const { Schema } = mongoose = require('mongoose');
const uri = 'mongodb://localhost:27017/test';
const opts = { useNewUrlParser: true, useUnifiedTopology: true };
mongoose.Promise = global.Promise;
mongoose.set('debug', true);
mongoose.set('useCreateIndex', true);
mongoose.set('useFindAndModify', false);
const transactionItemSchema = new Schema({
productId: String,
quantity: Number,
price: Number
});
const transactionSchema = new Schema({
details: String,
items: [transactionItemSchema]
},{
timestamps: true
});
const Transaction = mongoose.model('Transaction', transactionSchema);
const initialData = [
{
details: 'First Transaction',
items: [
{ price: 5.2, quantity: 2 },
{ price: 4, quantity: 3 }
]
},
{
details: 'Second Transaction',
items: [
{ price: 0.333, quantity: 3 }
]
}
];
const log = data => console.log(JSON.stringify(data, undefined, 2));
(async function() {
try {
const conn = await mongoose.connect(uri, opts);
// Clean data
await Promise.all(
Object.values(conn.models).map(m => m.deleteMany())
);
await Transaction.insertMany(initialData);
// Aggregate example
let result1 = await Transaction.aggregate([
{ "$addFields": {
"total": {
"$sum": {
"$map": {
"input": "$items",
"in": {
"$round": [
{ "$multiply": [ "$$this.price", "$$this.quantity" ] },
2
]
}
}
}
},
"items": {
"$map": {
"input": "$items",
"in": {
"$mergeObjects": [
"$$this",
{ "total": {
"$round": [
{ "$multiply": [ "$$this.price", "$$this.quantity" ] },
2
]
}}
]
}
}
}
}}
]);
log({ result1 });
// Plain JavaScript example
let result2 = await Transaction.find().lean();
result2 = result2.map(r =>
({
...r,
total: r.items.reduce((o, i) =>
o + parseFloat((i.price * i.quantity).toFixed(2)), 0),
items: r.items.map(i =>
({ ...i, total: parseFloat((i.price * i.quantity).toFixed(2)) })
)
})
);
log({ result2 });
} catch (e) {
console.error(e);
} finally {
mongoose.disconnect();
}
})();
And the output:
Mongoose: transactions.deleteMany({}, {})
Mongoose: transactions.insertMany([ { _id: 5d8f4dfcaf9f6a2f8ec28039, details: 'First Transaction', items: [ { _id: 5d8f4dfcaf9f6a2f8ec2803b, price: 5.2, quantity: 2 }, { _id: 5d8f4dfcaf9f6a2f8ec2803a, price: 4, quantity: 3 } ], __v: 0, createdAt: 2019-09-28T12:11:40.060Z, updatedAt: 2019-09-28T12:11:40.061Z }, { _id: 5d8f4dfcaf9f6a2f8ec2803c, details: 'Second Transaction', items: [ { _id: 5d8f4dfcaf9f6a2f8ec2803d, price: 0.333, quantity: 3 } ], __v: 0, createdAt: 2019-09-28T12:11:40.062Z, updatedAt: 2019-09-28T12:11:40.062Z } ], {})
Mongoose: transactions.aggregate([ { '$addFields': { total: { '$sum': { '$map': { input: '$items', in: { '$round': [ { '$multiply': [ '$$this.price', '$$this.quantity' ] }, 2 ] } } } }, items: { '$map': { input: '$items', in: { '$mergeObjects': [ '$$this', { total: { '$round': [ { '$multiply': [Array] }, 2 ] } } ] } } } } } ], {})
{
"result1": [
{
"_id": "5d8f4dfcaf9f6a2f8ec28039",
"details": "First Transaction",
"items": [
{
"_id": "5d8f4dfcaf9f6a2f8ec2803b",
"price": 5.2,
"quantity": 2,
"total": 10.4
},
{
"_id": "5d8f4dfcaf9f6a2f8ec2803a",
"price": 4,
"quantity": 3,
"total": 12
}
],
"__v": 0,
"createdAt": "2019-09-28T12:11:40.060Z",
"updatedAt": "2019-09-28T12:11:40.061Z",
"total": 22.4
},
{
"_id": "5d8f4dfcaf9f6a2f8ec2803c",
"details": "Second Transaction",
"items": [
{
"_id": "5d8f4dfcaf9f6a2f8ec2803d",
"price": 0.333,
"quantity": 3,
"total": 1
}
],
"__v": 0,
"createdAt": "2019-09-28T12:11:40.062Z",
"updatedAt": "2019-09-28T12:11:40.062Z",
"total": 1
}
]
}
Mongoose: transactions.find({}, { projection: {} })
{
"result2": [
{
"_id": "5d8f4dfcaf9f6a2f8ec28039",
"details": "First Transaction",
"items": [
{
"_id": "5d8f4dfcaf9f6a2f8ec2803b",
"price": 5.2,
"quantity": 2,
"total": 10.4
},
{
"_id": "5d8f4dfcaf9f6a2f8ec2803a",
"price": 4,
"quantity": 3,
"total": 12
}
],
"__v": 0,
"createdAt": "2019-09-28T12:11:40.060Z",
"updatedAt": "2019-09-28T12:11:40.061Z",
"total": 22.4
},
{
"_id": "5d8f4dfcaf9f6a2f8ec2803c",
"details": "Second Transaction",
"items": [
{
"_id": "5d8f4dfcaf9f6a2f8ec2803d",
"price": 0.333,
"quantity": 3,
"total": 1
}
],
"__v": 0,
"createdAt": "2019-09-28T12:11:40.062Z",
"updatedAt": "2019-09-28T12:11:40.062Z",
"total": 1
}
]
}