Group by one of multiple fields matching - mongodb

Question

I have a collection of documents (grades) with some missing keys like this:
Name
ID
Github
Points
Peter
1
123
1
PPane
456
Alice
Alice1
234
2
Alice1
567
I want to group this data by matching any of Name, ID or Github together and collecting the points.
The result should look like this:
_id
Points
[Peter, 1, PPane]
[123, 456]
[Alice, 2, Alice1]
[234, 567]
Right now I am doing this in the backend like this:
const students = new Map<string, CourseStudent>();
const keys = ['Name', 'ID', 'Github'];
for (const grade of grades) {
let student: CourseStudent | undefined = undefined;
for (const key of keys) {
const value = grade[key];
if (value && (student = students.get(value))) {
break;
}
}
if (!student) {
const {Name, ID, Github} = grade;
student = {_id: {Name, ID, Github}, points: []};
}
for (const key of keys) {
const value = grade[key];
if (value) {
students.set(value, student);
}
}
student.points.push(grade.points);
}
return Array.from(students.values());
The data sizes in my use case are 1000-10000 grades (100-1000 students x 10 assignments).
The actual "grade" data contains a lot more fields, most of which are not used for the final result, but keeping all of it in memory can be costly.
Is there a way to achieve this in the database with an aggregation pipeline, e.g. using $group?
To start with, here is a non-working aggregation, because it requires ALL fields to match instead of just one:
{$group: {_id: ['$Name', '$ID', '$Github'], points: {$push: '$Points'}}},

Answer 1

Since you have only 3 keys to use, grouping by one and collecting the 2 others will result in one missing key only:
$group by ID and collect other keys. Assuming there is at least one document per each user which contains the user's key (as in your example), this step will result with number of documents as the number of users + 1. Each document contains the user ID and Name or Github. One document refer all document without any ID.
$match to keep only the users documents
For each user document get all the matching original documents using $lookup, we now have the data needed to get them.
Group and format the results.
db.collection.aggregate([
{$group: {_id: "$ID", Name: {$first: "$Name"}, Github: {$first: "$Github"}}},
{$match: {_id: {$ne: null}}},
{$lookup: {
from: "collection",
let: {github: "$Github", iD: "$_id"},
pipeline: [
{$match: {
$expr: {$or: [
{$eq: ["$$github", "$Github"]},
{$eq: ["$$iD", "$ID"]}
]}
}},
{$group: {
_id: 0,
Name: {$addToSet: "$Name"},
Github: {$addToSet: "$Github"},
ID: {$addToSet: "$ID"},
Points: {$push: "$Points"}
}}
],
as: "docs"
}
},
{$replaceRoot: {newRoot: {$first: "$docs"}}},
{$project: {
_id: [{$first: "$Name"}, {$first: "$ID"}, {$first: "$Github"}],
Points: 1
}}
])
See how it works on the playground example