MongoDB $lookup based on two schema - database

Question

I would like to know how to query in mongo db based on two other schema collection.
I have 3 schema's in mongo db:
1. Site : {_id, name}
2. Components : { _id, siteId, details }
3. Maintenance : { _id, siteId }
I want to query and get all the components with site information and at same time ensuring that they are not in maintenance.
I am able to fetch components with site information with following query:
componentCollection
.aggregate([
{
$lookup: {
from: 'sites',
localField: 'siteId',
foreignField: '_id',
as: 'sites',
},
},
])
How to update this query so that I can ensure selected components site's are not in maintenance collection?
Update with sample data, expected and current output:
`Site`
---------------------------
_id | name
---------------------------
1 | site1
---------------------------
2 | site2
---------------------------
`Components`
---------------------------
_id | siteId | details
---------------------------
3 | 1 | help & support
---------------------------
4 | 2 | footer links
---------------------------
`Maintenance`
---------------------------
_id | siteId
---------------------------
5 | 1
---------------------------
With the above sample query I am getting the following result:
[
{
_id: 3,
siteId: 1,
details: 'help & support',
sites: [
{
_id: 1,
name: 'site1'
}
]
},
{
_id: 4,
siteId: 2,
details: 'footer links',
sites: [
{
_id: 2,
name: 'site2'
}
]
}
]
But I want only below, as site1 is in maintenance mode
[
{
_id: 4,
siteId: 2,
details: 'footer links',
sites: [
{
_id: 2,
name: 'site2'
}
]
}
]

Answer 1

This might help you.
Join the Components Collection and Site Collection
Nested join the Site and Maintenance. Because if Maintenance has the Site, we can easily eliminate the object.
Filter out the object in the Site array if joinMaintenance is an empty array using $filter.
So if joinMaintenance doesn't have any objects, it will exist in Sites
Here is the code
[
{
"$lookup": {
"from": "Site",
"let": {
"sId": "$siteId"
},
"pipeline": [
{
$match: {
$expr: {
$eq: [
"$_id",
"$$sId"
]
}
}
},
{
$lookup: {
from: "Maintenance",
let: {
"smId": "$_id"
},
pipeline: [
{
"$match": {
$expr: {
$eq: [
"$siteId",
"$$smId"
]
}
}
}
],
as: "joinMaintenance"
}
}
],
as: "sites"
}
},
{
$project: {
details: 1,
siteId: 1,
sites: {
$filter: {
input: "$sites",
cond: {
$eq: [
"$$this.joinMaintenance",
[]
]
}
}
}
}
},
{
$match: {
$expr: {
$ne: [
"$sites",
[]
]
}
}
},
{
$project: {
"sites.joinMaintenance": 0
}
}
]
Working Mongo playground