Mongo. Return related collections on parent - node.js

Question

Assuming such a mongoose database schema,
const teacherSchema = new mongoose.Schema({
name: {type: String, required: true, trim: true},
})
const courseSchema = new mongoose.Schema({
name: {type: String, required: true, trim: true},
teacher: { type: 'ObjectId', ref: 'Teacher', required: true },
})
const studentSchema = new mongoose.Schema({
name: {type: String, required: true, trim: true},
course: { type: 'ObjectId', ref: 'Course', required: true },
})
const hobbySchema = new mongoose.Schema({
name: {type: String, required: true, trim: true},
student: { type: 'ObjectId', ref: 'Student', required: true },
})
How can I query and return data from a specific teacher, while nesting courses they teach, students taking the course and their hobbies?
NOTE: I find teacher using url params (id)
{
_id: "61040a6dec6d054128fa8eae",
name: "John Doe",
others: ...,
courses: [
{
content: ...,
students: [
{
content: ....,
hobbies: [{
content:...
}
]
},
{...other students taking the course}
]
},
{...other subjects by John Doe}
]
}

Answer 1

All you need is mongo aggregate to link and obtain data from different schemas.
First, introduce a relationship linking all schemas, just like how you doing with the ref, I suggest have a
usersSchema and introduce a userType field that identifies the type of user either student or teacher, so you can do away with teacherSchema and studentSchema
UserSchema.aggregate([
{
$match: { id: teacherId }
},
{
$lookup: {
from: "users",
localField: "students",
foreignField: "_id",
as: "students",
},
},
{
$lookup: {
from: "hobbies",
localField: "hobbyId",
foreignField: "_id",
as: "hobbies",
},
},
{
$lookup: {
from: "course",
localField: "courseId",
foreignField: "_id",
as: "courses",
},
},
{
$sort: {
createdAt: -1,
},
},
{
$unwind: "$users",
},
])
.then((data) => {
return data
})