Nodejs mongodb API performance - node.js

Question

I want to create an API which will query users in my mongodb and returns the data of all users. For each user i need to perform additional query to get count in 2 other schema as below:
const getUsersSummary = async (req, res, next) => {
try {
const users = await User.fetch();
const usersWithCount = await Promise.all(
users.map(async (user) => {
let tests;
let enrollments;
try {
tests = await Test.countDocuments(
{ user: user._id }
);
enrollments = await Enrollment.countDocuments(
{ user: user._id }
);
} catch (e) {
tests = 0;
enrollments = 0;
}
return {
_id: user._id,
name: user.name,
address: user.address,
tests: tests,
enrollments: enrollments,
};
})
);
return res.json({
users: usersWithCount,
});
} catch (err) {
next(err);
}
};
I want to know if this is a good way to do it.
The code works. But i am concerned about the performance and load it will put on my server.

Answer 1

I think you might consider use the MongoDB aggregation framework. You can combine user data with trial and registration data using the $lookup operator to join the user data with the tests and enrollments data, and then use the $group operator to get the count of tests and enrollments for each user. This will reduce the number of database queries and improve the performance of your API.
const aggregate = User.aggregate([
{
$lookup: {
from: "tests",
localField: "_id",
foreignField: "user",
as: "tests"
}
},
{
$lookup: {
from: "enrollments",
localField: "_id",
foreignField: "user",
as: "enrollments"
}
},
{
$project: {
_id: 1,
name: 1,
address: 1,
tests: { $size: "$tests" },
enrollments: { $size: "$enrollments" }
}
}
]);
const usersWithCount = await aggregate.exec();
return res.json({
users: usersWithCount,
});