Mongodb find document in collection from field in another collection - mongodb

Question

I have two collections: Sharing and Material.
Sharing:
{
from_id: 2
to_id: 1
material_id: material1
}
Material:
{
_id: material1
organization_id: 2
},
{
_id: material2
organization_id: 1
},
{
_id: material3
organization_id: 1
},
--Edit:
There are three materials, 2 belong to organization_id(1) and 1 belongs to organization_id(2). The organization_id does not match 1 in material1 (and instead belongs to material2), but in the Sharing collection, the to_id does match 1. If the match exists, I'd like to find the Material document _id which is equal to the material_id of Sharing AND find the Material documents where the organization_id is equal to 1.
I'd like to check if a field in Sharing (to_id) has a value that is equal to a field in Material (organization_id) AND check if organization_id is equal to 1. If there is a document that exists from this, do another check to find whether the _id of Material is equal to the material_id of Sharing and return all documents & the total count.
If there is no equal value, I'd like to omit that result and send the object with only organization_id equal to 1 and get the total count of this result.
Right now, I do it in a very inefficient way using .map() to find this. Below is my code:
export const getMaterials = async (req, res) => {
const sharing = await Sharing.find({to_id: 1});
let doneLoad;
try {
if (sharing && sharing.length>0) {
const sharingTotal = await Material.find( {$or: [ {organization_id: 1}, {_id: sharing.map((item) => item.material_id)} ] } ).countDocuments();
const sharingMats = await Material.find( {$or: [ {organization_id: 1}, {_id: sharing.map((item) => item.material_id)} ] } );
res.status(200).json({data: sharingMats});
doneLoad= true;
}
else if (!doneLoad) {
const materialTotal = await Material.find({organization_id: 1}).countDocuments();
const materials = await Material.find({organization_id: 1});
res.status(200).json({data: materials});
}
} catch (error) {
res.status(404).json({ message: error.message });
}
}
I have tried using aggregation to get my desired result but I cannot find any solution that fits my requirements. Any help would be great as I am quite new to using mongodb. Thanks.
Edit (desired result):
Materials: [
{
_id: material1,
organization_id: 1
},
{
_id: material2,
organization_id: 1
},
{
_id: material3,
organization_id: 1
}
]

Answer 1

You can use sub-pipeline in a $lookup to perform the filtering. $addFields the count using $size later.
db.Sharing.aggregate([
{
"$match": {
to_id: 1
}
},
{
"$lookup": {
"from": "Material",
"let": {
to_id: "$to_id",
material_id: "$material_id"
},
"pipeline": [
{
"$match": {
$expr: {
$or: [
{
$eq: [
"$$to_id",
"$organization_id"
]
},
{
$eq: [
"$$material_id",
"$_id"
]
}
]
}
}
},
{
"$addFields": {
"organization_id": 1
}
}
],
"as": "materialLookup"
}
},
{
"$addFields": {
"materialCount": {
$size: "$materialLookup"
}
}
}
])
Here is the Mongo playground for your reference.