How to populate array of objects in mongoose - mongodb

Question

I have this code -
const getAllCourses = async (req, res) => {
const courses = await Course.find({});
try {
await courses.populate('professor')
res.send({ status: 200, data: { courses } });
} catch (err) {
res.status(500).send({ status: 500, message: "Internal server error." });
}
};
Also, this is the response I'm getting from postman -
{
"status": 200,
"data": {
"courses": [
{
"_id": "61dc47f58f88c1a7e9bd36b6",
"name": "Course1",
"professor": "61dc1299431cd669faad7d0f",
"students": [
{
"student": "61dc0b7f103b531f105e8e4c",
"_id": "61dc47f58f88c1a7e9bd36b7"
},
{
"student": "61dc220885886a9f1d8e94d0",
"_id": "61dc47f58f88c1a7e9bd36b8"
}
],
"createdAt": "2022-01-10T14:51:33.313Z",
"updatedAt": "2022-01-10T14:51:33.313Z",
"__v": 0
},
{
"_id": "61dc47fb8f88c1a7e9bd36bf",
"name": "Course2",
"professor": "61dc1299431cd669faad7d0f",
"students": [
{
"student": "61dc0b7f103b531f105e8e4c",
"_id": "61dc47fb8f88c1a7e9bd36c0"
},
{
"student": "61dc220885886a9f1d8e94d0",
"_id": "61dc47fb8f88c1a7e9bd36c1"
}
],
"createdAt": "2022-01-10T14:51:39.704Z",
"updatedAt": "2022-01-10T14:51:39.704Z",
"__v": 0
}
]
}
}
Now what I'm trying to do is to populate the professor and the students but it doesn't seem to work.
I tried populating "courses.professor", "course.professor", "professor" but nothing worked for me.
What am I missing?

Answer 1

Here is an example of how this can be done for a document with an array friends on it:
User.
findOne({ name: 'Val' }).
populate({
path: 'friends',
// Get friends of friends - populate the 'friends' array for every friend
populate: { path: 'friends' }
});

Answer 2

I just solved it by chaining the populate method directly after the Course.find({}) and it just worked, I'm not sure why though.
Solution:
const getAllCourses = async (req, res) => {
const courses = await Course.find({}).populate('professor').populate('students.student');
try {
res.send({ status: 200, data: { courses } });
} catch (err) {
res.status(500).send({ status: 500, message: err.message });
}
};