mongodb update query in aggregation from multiple collections without grouping - node.js

Question

can i update specific fields in a particular collection according to the matched keys from different collections i.e suppose i have 3 collections
**///collection 1: col1///**
_id:ObjectId("#####7b")
name:'name1',
itemsBought:
[
{
"_id":ObjectId("####c1"
"itemName" : "name1",
"itemCode" : "IT001",
"itemQuantity" : 19,
"itemPrediction":23
},
{
"_id":ObjectId("####c2"
"itemName" : "name2",
"itemCode" : "IT002",
"itemQuantity" : 79,
"itemPrediction":69
},
{
"_id":ObjectId("####c3"
"itemName" : "name2",
"itemCode" : "IT003",
"itemQuantity" : 0,
"itemPrediction":0
},
]
**///collection 1: col2///**
{
"itemQuantity" : 21,
"itemCode" : "IT001",
},
{
"itemQuantity" : 2,
"itemCode" : "IT003",
}
**///collection 1: col3///**
{
"itemCode" : "IT001",
"itemPrediction":23
},
{
"itemCode" : "IT002",
"itemPrediction":12
},
{
"itemCode" : "IT003",
"itemPrediction":7
},
i am using $aggregation $lookup to fetch out all the required data, before sending it to the frontend i need to fetch the values of itemQuantity from col2 and itemPrediction from col3 and update that in col1 with the matching itemCode. So i have the query which fetches out all the data from all the collections but i dont know how to use $set to update the values in col1.

Answer 1

Workaround: You may perform aggregation and save the result manually
db.col1.aggregate([
{
$lookup: {
from: "col2",
let: {
root_itemCode: "$itemsBought.itemCode"
},
pipeline: [
{
$match: {
$expr: {
$in: [
"$itemCode",
"$$root_itemCode"
]
}
}
}
],
as: "col2"
}
},
{
$lookup: {
from: "col3",
let: {
root_itemCode: "$itemsBought.itemCode"
},
pipeline: [
{
$match: {
$expr: {
$in: [
"$itemCode",
"$$root_itemCode"
]
}
}
}
],
as: "col3"
}
},
{
$addFields: {
itemsBought: {
$map: {
input: "$itemsBought",
as: "item",
in: {
"_id": "$$item._id",
"itemName": "$$item.itemName",
"itemCode": "$$item.itemCode",
"itemQuantity": {
$let: {
vars: {
input: {
$arrayElemAt: [
{
$filter: {
input: "$col2",
cond: {
$eq: [
"$$item.itemCode",
"$$this.itemCode"
]
}
}
},
0
]
},
default: "$$item.itemQuantity"
},
in: {
$ifNull: [
"$$input.itemQuantity",
"$$default"
]
}
}
},
"itemPrediction": {
$let: {
vars: {
input: {
$arrayElemAt: [
{
$filter: {
input: "$col3",
cond: {
$eq: [
"$$item.itemCode",
"$$this.itemCode"
]
}
}
},
0
]
},
default: "$$item.itemPrediction"
},
in: {
$ifNull: [
"$$input.itemPrediction",
"$$default"
]
}
}
}
}
}
}
}
},
{
$unset: [
"col2",
"col3"
]
}
])
MongoPlayground
Mongoose
Collection1.aggregate([...], function (err, result) {
if(err) console.log("error-agg: " + err);
result.forEach(function(item) {
Collection1.updateOne({_id:item._id}, {$set:item}, function (err) {
if(err) console.log("error-saving: " + err);
});
});
});