Nodejs localField $lookup as Array of _ids - node.js

Question

i need to join two documents where in the first there a property as array of _ids and in the second documents to join
db={
"tipo_pratica": [
{
"_id": "618981a4c1b8b3bc67ff80b6",
"descrizione": "anticipata",
"modulo": [
"628015cd2fd9dfee86ac6820",
"62801a4c2fd9dfee86ac6821",
"6278f8d9d4aa4f4cef1a8266"
]},
{
"_id": "628238d6f97b57efcb1fc504",
"descrizione": "Supporto",
"modulo": [
"6278f8d9d4aa4f4cef1a8266",
"628015cd2fd9dfee86ac6820",
"62801a4c2fd9dfee86ac6821"
]}
]};
db={
"moduli": [
{
"_id": "6278f8d9d4aa4f4cef1a8266",
"tipo": "Incentivi auto",
"documento": [
"1652095190015_la_scuola_2021_copia.pdf"
],
"contenuto": "<p>Inserire il documento allegato</p>"
},
{
"_id": "628015cd2fd9dfee86ac6820",
"tipo": "Mandato di assistenza e rappresentanza",
"documento": [
"1652561335432_Mandato_di_rappresentanza_privacy_0.pdf"
],
"contenuto": "<p>no</p>"
},
{
"_id": "62801a4c2fd9dfee86ac6821",
"tipo": "Modello red da far... ",
"documento": [
"1652562502599_Modello_REX.pdf"
],
"contenuto": null
}]
};
as documentation said:
Use $lookup with an Array
I tried:
const doc = await collection.aggregate([
{
$lookup: {
from: "moduli",
localField: "modulo",
foreignField: "_id",
as: "moduls"
}
}
])
with no success
so i tested the script on mongoplayground
and there it seems to work well.
I think the problem reside in array of Ids, also
i have tried many option, i have often read the documentation and serching on the web, but many results are specific to mongoose drive, while i use native drive.
I would like the same return as the playground example.
So, any help is largely apprecciate.
below the snippet i use in node for make call
app.post('/admin/moduli/join/', (req, res, error) => {
async function run() {
try {
await client.connect();
var ObjectId = require('mongodb').ObjectId;
const db = client.db("admin");
const collection = db.collection("tipo_pratica");
// replace IDs array with lookup results passed to pipeline
const doc = await collection.aggregate([
{
$lookup: {
from: "moduli",
localField: "modulo",
foreignField: "_id",
pipeline: [
{ $match: { $expr: {$in: ["$_id", "$$modulo"] } } },
{ $project: {_id: 0} } // suppress _id
],
as: "productObjects"
}
}
]);
// doc not work!
// Unwind
const doc2 = await collection.aggregate([
// Unwind the source
{ "$unwind": "$modulo" },
// Do the lookup matching
{ "$lookup": {
"from": "moduli",
"localField": "modulo",
"foreignField": "_id",
"as": "productObjects"
}
}
// doc2 not work!
const doc3 = await collection.aggregate([
{
$facet: {
moduli: [
{
$lookup: {
from: "moduli",
localField: "modulo",
foreignField: "_id", // also tried ObjectId()
as: "plugin"
}
},
{
$match: {
plugin: {
$not: {
$size: 0
}
}
}
}
]
}
},
{
$project: {
tipoPratiche: {
"$concatArrays": [
"$moduli"
]
}
}
},
{
$unwind: "$tipoPratiche"
},
]).toArray();
// doc3 not work!
res.send(doc4);
} finally {
await client.close();
}
}
run().catch(console.dir);
});
Thank you in advance for your time

Answer 1

One way to do it is using a $map before the $lookup:
db.tipo_pratica.aggregate([
{
$set: {
modulo: {
$map: {
input: "$modulo",
as: "item",
in: {$toObjectId: "$$item"}
}
}
}
},
{
$lookup: {
from: "moduli",
localField: "modulo",
foreignField: "_id",
as: "moduls"
}
}
])
Playground
Another option is to use a $lookup pipeline and cast the string to ObjectId inside it.

Answer 2

The proble reside in the formatting text. So belove the solution
const doc1 = await db.collection("tipo_pratica").aggregate([
{
'$set': {
'modulo': {
'$map': {
'input': '$modulo',
'as': 'item',
'in': {
'$toObjectId': '$$item'
}
}
}
}
}, {
'$lookup': {
'from': 'moduli',
'localField': 'modulo',
'foreignField': '_id',
'as': 'moduls'
}
}
]).toArray();