mongoDB lookups upto 4-5 levels with arrays - mongodb

Question

I am trying to create aggregate code which can join multiple collections and fetches data based on the condition
My collections looks like the following
Users Collection(Example Document)
{
"_id":{"$oid":"6137038058d4632824c84872"},
"first_name":"test",
"last_name":".",
"email":"valid#gmail.com",
"enrolled_courses":[
{
"completed_lessons":[],
"completed":false,
"_id": {"$oid":"6142d1c76d657428903420db"},
"course_id":{"$oid":"614033510a61aa1f3c8b94ff"}
},
{
"completed_lessons":[],
"completed":false,
"_id":{"$oid":"6156d686dcbc58503c7ec679"},
"course_id":{"$oid":"61486e57460b5a422c6e63ca"}
},
{
"completed_lessons":["616d181e62cb265db07d9273","616d182e62cb265db07d9293"],
"completed":false,
"_id":{"$oid":"616d2424149936380c186c2d"},
"course_id":{"$oid":"616d105662cb265db07d91cf"}
}
]
}
Courses Collection(Example Document)
{
"_id":{"$oid":"6135f735b399f03ba03d74ce"},
"type":1,
"enrolled_users":["61374040c27237b1ed87480b"],
"is_deleted":0,
"status":1,
"company_id":{"$oid":"6135f6c9b399f03ba03d74a0"},
"course":"Course 1"
}
Modules Collection(Example Document)
{
"_id":{"$oid":"616d17fd62cb265db07d9240"},
"type":1,
"is_always_available":false,
"is_deleted":0,
"status":1,
"company_id":{"$oid":"6135f6c9b399f03ba03d74a0"},
"course_id":{"$oid":"616d105662cb265db07d91cf"},
"module_name":"module 3",
"due_date":{"$date":"2021-10-18T00:00:00.000Z"}
}
Lessons Collection(Example Document)
{
"_id":{"$oid":"616d184962cb265db07d92cb"},
"lessson_image":null,
"status":1,
"is_deleted": 0,
"module_id":{"$oid":"616d17e462cb265db07d921f"},
"lessson_name":"Lesson 3"
}
I want to fetch details of all the courses user have enrolled and fetch all course's modules and its lessons
My expected output should be like following -
[
{
//CourseDetail 1 Keys,
modules: [
{
//Module Details
lessons: [{
//lessons of this module
}]
},
{
//Module Details
lessons: [{
//lessons of this module
}]
}
]
},
{
//CourseDetail 2 Keys,
modules: [
{
//Module Details
lessons: [{
//lessons of this module
}]
},
{
//Module Details
lessons: [{
//lessons of this module
}]
}
]
}
]
My current query is following, what it currently does is it groups the modules and its lessons together and bind it to single course object. The fetching of modules and lessons is perfect as per my requirement but course array contains only 1 single object and it holds list of all the modules from other courses also.
Current Query Code
let courseDetails = await users.aggregate([
{
$match: { _id: mongoose.Types.ObjectId(user._id), }
},
{$unwind:"$enrolled_courses"},
{
$lookup: {
from: 'courses',
localField: "enrolled_courses.course_id",
foreignField: "_id",
as: "courseDetails"
}
},
{ $unwind: { path: "$courseDetails", preserveNullAndEmptyArrays: true}},
{
$lookup: {
from: "modules",
let: { currentCourseId: "$courseDetails._id"},
pipeline: [{
$match: {
$expr: {
$and: [
{ $eq: ["$course_id", "$$currentCourseId"]},
{ $eq: ["$status", 1]},
{ $eq: ["$is_deleted", 0]},
{
$or: [
{ $eq: ["$is_always_available", true] },
{ $gte: ["$due_date", convertedDate]}
]
}
]
}
}
},
{
$project: {
_id: 1,
module_name: 1,
company_id: 1,
course_id: 1
}
}],
as: "moduleList"
}
},
{ $unwind: { path: "$moduleList", preserveNullAndEmptyArrays: true }},
{
$lookup: {
from: "lessons",
let: { curentModuleId: "$moduleList._id"},
pipeline: [{
$match: {
$expr: {
$and: [
{ $eq: ["$status", 1] },
{ $eq: ["$is_deleted", 0]},
{ $eq: ["$module_id", "$$curentModuleId"]}
]
}
}
}, {
$project: {
_id: 1,
lessson_name: 1,
module_id: 1
}
}],
as: "moduleList.lessons"
}
},
{
$group: {
_id: "$_id",
course_id: { $first: "$enrolled_courses.course_id"},
course_name: { $first: "$courseDetails.course"},
completed_lessons: { $first: "$enrolled_courses.completed_lessons"},
current_lessons: { $first: "$enrolled_courses.current_lessons"},
completed: { $first: "$enrolled_courses.completed"},
enrolled_users_count: {
$first: "$courseDetails.enrolled_users"
},
modules: {
$push: "$moduleList"
}
}
},
{
$project: {
course_id: 1,
course_name: 1,
completed_lessons: 1,
current_lessons: 1,
completed: 1,
enrolled_users_count: {
$size: "$enrolled_users_count"
},
modules: 1
}
},
{
$group: {
_id: "$_id",
course_id: { $first: "$course_id"},
course_name: { $first: "$course_name"},
completed_lessons: { $first: "$completed_lessons"},
current_lessons: { $first: "$current_lessons"},
completed: { $first: "$completed"},
enrolled_users_count: { $first: "$enrolled_users_count"},
modules: { $first: "$modules"}
}
}
]);