MongoDB multiple $lookup and $group output - mongodb

Question

I'm quite a newbie with MongoDB and I'm trying to retrieve a kind-of leaderboard based on two related collections and a third one, referencing one of the two, based on its different property.
Schema can be found here
Consider a schema like the following one:
tree: { _id, company_id: string, company_name }
link: { _id, company_id: string, url: string }
analytics: { _id, tree_id: string, link_id: string, views: number, clicks: number, date: string }
A analytics document can have tree_id, views or link_id, clicks at once.
What I'm trying to achieve right now is a kind-of a "leaderboard" of the total clicks + views, starting from analytics collection, joining it with both tree and link, and finally retrieving the sum of clicks and views.
I have already managed to retrieve the sum of them for a specific company_id, with the following code
db.analytics.aggregate([{
$lookup: {
from: "trees",
as: "trees",
localField: "tree_id",
foreignField: "_id"
}
}, {
$lookup: {
from: "links",
as: "links",
localField: "link_id",
foreignField: "_id"
}
}, {
$match: {
$or: [
{"trees.company_id": "1"},
{"links.company_id": "1"}
]
}
}, {
$group: {
_id: null,
views_count: {
$sum: "$views"
},
clicks_count: {
$sum: "$clicks"
}
}
}])
But I can't find a way to get a list of results like
{ company_id: 1, company_name: "foo", clicks: 100, views: 200 },
{ company_id: 2, company_name: "bar", clicks: 200, views: 200 }
and so on.
What I've tried so far is grouping by different _id, which is not working as I would expect
db.analytics.aggregate([{
$lookup: {
from: "trees",
as: "trees",
localField: "tree_id",
foreignField: "_id"
}
}, {
$lookup: {
from: "links",
as: "links",
localField: "link_id",
foreignField: "_id"
}
}, {
$group: {
_id: "$trees.company_id",
views_count: {
$sum: "$views"
},
clicks_count: {
$sum: "$clicks"
}
}
}])
Which does not assign clicks_count to a specific entry, but outputs something like
{ "_id" : [ "1" ], "views_count" : 6, "clicks_count" : 0 }
{ "_id" : [ ], "views_count" : 0, "clicks_count" : 48 }
{ "_id" : [ "2" ], "views_count" : 10, "clicks_count" : 0 }
I'm not even sure that this schema could be the best solution, so I will also appreciate any design suggestions or similar stuff.
Based on the comment below, I tried to deconstruct trees before grouping results, but it ended outputting the company_id, views_count only, without counting clicks, as following
{ "_id" : "2", "views_count" : 10, "clicks_count" : 0 }
{ "_id" : "1", "views_count" : 6, "clicks_count" : 0 }

Answer 1

$addFields to add company field, check condition if trees.company_id not empty [] then return trees otherwise return links
$arrayElemAt to get first element from array
$group by company_id and sum your counts
db.analytics.aggregate([
{ $lookup: { //... } },
{ $lookup: { //... } },
{
$addFields: {
company: {
$arrayElemAt: [
{ $cond: [{ $ne: ["$trees.company_id", []] }, "$trees", "$links"] },
0
]
}
}
},
{
$group: {
_id: "$company.company_id",
company_name: { $first: "$company.company_name" },
views_count: { $sum: "$views" },
clicks_count: { $sum: "$clicks" }
}
}
])
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