Mongoose query on multiple populated fields - mongodb

Question

I have three collections i.e Events, News and FuneralNews.
I have another Notifications collection that is just a combination of all three and contains the reference Id of either/one of the three collections.
I want to fetch only those Notifcations whose eventId OR newsId OR funeralNewsId field isActive is true
EventsSchema:
var EventsSchema = new Schema({
...
isActive: Boolean
});
FuneralNewsSchema:
var FuneralNewsSchema = new Schema({
...
isActive: Boolean
});
NewsSchema:
var NewsSchema = new Schema({
...
isActive: Boolean
});
NotificationSchema:
var NotificationSchema = new Schema({
type: {
type: String,
required: true
},
creationDate: {
type: Date,
default: Date.now
},
eventId: {type: Schema.Types.ObjectId, ref: 'Events'},
newsId: {type: Schema.Types.ObjectId, ref: 'News'},
funeralNewsId: {type: Schema.Types.ObjectId, ref: 'FuneralNews'},
organisationId: {type: Schema.Types.ObjectId, ref: 'Organization'}
});
This was my query before I need a check on isActive property of referenced collection:
let totalItems;
const query = { organisationId: organisationId };
Notification.find(query)
.countDocuments()
.then((count) => {
totalItems = count;
return Notification.find(query, null, { lean: true })
.skip(page * limit)
.limit(limit)
.sort({ creationDate: -1 })
.populate("eventId")
.populate("newsId")
.populate("funeralNewsId")
.exec();
})
.then((notifications, err) => {
if (err) throw new Error(err);
res.status(200).json({ notifications, totalItems });
})
.catch((err) => {
next(err);
});
Now I don't know how to check on isActive field of three populated collections prior population.
I have seen other questions like this and this but being a newbie can't edit it according to my use-case. Any help would be highly appreciated

Answer 1

use $lookup for each objectId refrence
then group by _id of null to get data and add myCount as total number put original data to array
and use unwind to destruct array and use addField
model
.aggregate([
{
$lookup: {
from: "Events", // events collection name
localField: "eventId",
foreignField: "_id",
as: "events",
},
},
{
$lookup: {
from: "FuneralNews", //FuneralNews collection name
localField: "funeralNewsId",
foreignField: "_id",
as: "funeralnews",
},
},
{
$lookup: {
from: "News", // news collection name
localField: "newsId",
foreignField: "_id",
as: "news",
},
},
{
$match: {
$or: [
{ "news.isActive": true },
{ "events.isActive": true },
{ "funeralnews.isActive": true },
],
},
},
{
$group: {
_id: null,
myCount: {
$sum: 1,
},
root: {
$push: "$$ROOT",
},
},
},
{
$unwind: {
path: "$root",
},
},
{
$addFields: {
"root.total": "$myCount",
},
},
{
$replaceRoot: {
newRoot: "$root",
},
},
{
$sort: {
creationDate: -1,
},
},
])
.skip(page * limit)
.limit(limit);