Mongodb aggregation distinct, average and sum with group by between two collection - node.js

Question

I have user collection having data like this
{
"_id" : ObjectId("5da594c15324fec81d000027"),
"password" : "******",
"activation" : "Active",
"userType" : "Author",
"email" : "something#gmail.com",
"name" : "Something",
"profilePicture" : "profile_pictures/5da594c15324fec81d0000271607094354423image.png",
"__v" : 0
}
and On the other hand userlogs has data like this
{
"_id" : ObjectId("5fcb7bb4485c34a41900002b"),
"duration" : 2.54,
"page" : 1,
"activityDetails" : "Viewed Page for seconds",
"contentType" : "article",
"activityType" : "articlePageStayTime",
"label" : 3,
"bookId" : ObjectId("5f93e2cc74153f8c1800003f"),
"ipAddress" : "::1",
"creator" : ObjectId("5da594c15324fec81d000027"),
"created" : ISODate("2020-12-05T12:23:16.867Z"),
"__v" : 0
}
What I am trying to do is equivalent to this sql query
SELECT name,count(page),sum(duration),avg(DISTINCT(label)),COUNT(DISTINCT(bookId)) FROM users JOIN userlogs ON users._id=userlogs.creator where userlogs.activityType<>"articleListeningTime" group by users._id.
I can do normal group by and sum together.But How to do avg distinct and count distinct with this? I am using mongodb version 3.2

Answer 1

I don't think this require $group stage, you can use $setUnion and $size, $avg operators,
$lookup with userlogs collection
$project to show required fields, and filter userlogs as per your condition
$project to get statistics from userlogs
get total logs count using $size
get total duration sum using $sum
get average of unique label using $setUnion and $avg
get count of unique bookId using $serUnion and $size
db.users.aggregate([
{
$lookup: {
from: "userlogs",
localField: "_id",
foreignField: "creator",
as: "userlogs"
}
},
{
$project: {
name: 1,
userlogs: {
$filter: {
input: "$userlogs",
as: "u",
cond: { $ne: ["$$u.activityType", "articleListeningTime"] }
}
}
}
},
{
$project: {
name: 1,
totalCount: { $size: "$userlogs" },
durationSum: { $sum: "$userlogs.duration" },
labelAvg: { $avg: { $setUnion: "$userlogs.label" } },
bookIdCount: { $size: { $setUnion: "$userlogs.bookId" } }
}
}
])
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