Why should you care?

A course platform needs “all courses for a user” and “all users in a course”. Arrays work until relationships need progress percent or joinedAt.

See it live — copy this example

Open mongosh or MongoDB Compass, select database nosqlverse, then run the example. Change one field and run again.

db.users.insertOne({ _id: 1, name: "Isha", courseIds: [10, 20] })
db.courses.insertMany([
  { _id: 10, title: "MongoDB Basics", studentIds: [1, 2] },
  { _id: 20, title: "Aggregation", studentIds: [1] }
])
// Relationship with metadata
db.enrollments.insertOne({
  userId: 1, courseId: 10, progress: 40, enrolledAt: new Date()
})
db.enrollments.find({ userId: 1 })

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Arrays of ids are a simple many-to-many.
• enrollments adds progress metadata — better when the link itself has fields.
• Query enrollments by userId to list courses with progress.

Practice next

1. Seed users, courses, and one enrollment.
2. Find courses for user 1 via courseIds and via enrollments.
3. Add progress updates with updateOne on enrollments.
4. Query enrollments by courseId to list students.
5. Add a unique compound index to prevent double enroll.

Remember

Arrays of ids work for simple M:N. Use a join collection when links have data. Index relationship queries.

NoSQLVerse course enrollments

Learners enroll in many tutorials; each enrollment tracks percent complete.

Outcome: Progress UI reads enrollments without bloating the course catalog doc.