🧪 MongoDB Practice Questions with Solutions (Beginner to Advanced)

Learning MongoDB is not just about reading concepts—it’s about practicing real problems.

Here, you’ll solve hands-on MongoDB exercises step by step. Each question includes:

✅ Problem
✅ Solution
✅ Explanation

By the end, you’ll feel confident working with real-world MongoDB scenarios.

🟢 Level 1: Beginner Exercises

✅ Q1: Create a Database and Collection

Problem:
Create a database called school and a collection called students.

Solution:

use school
db.createCollection("students")

Explanation:
use school creates (or switches to) the database and createCollection() creates a new collection.

---

✅ Q2: Insert Documents

Problem:
Insert 3 student records with fields: name, age, course.

Solution:

db.students.insertMany([
  { name: "Amit", age: 20, course: "BCA" },
  { name: "Sara", age: 22, course: "MCA" },
  { name: "John", age: 19, course: "BSc" }
])

Explanation:
insertMany() allows inserting multiple documents at once.

---

✅ Q3: Find All Documents

Problem:
Retrieve all students from the collection.

Solution:

db.students.find()

Explanation:
find() returns all documents in the collection.

---

✅ Q4: Filter Data

Problem:
Find students with age greater than 20.

Solution:

db.students.find({ age: { $gt: 20 } })

Explanation:
$gt means "greater than".

🟡 Level 2: Intermediate Exercises

✅ Q5: Update a Document

Problem:
Update "Amit"’s course to "B.Tech".

Solution:

db.students.updateOne(
  { name: "Amit" },
  { $set: { course: "B.Tech" } }
)

Explanation:
$set updates specific fields.

---

✅ Q6: Delete a Document

Problem:
Delete the student named "John".

Solution:

db.students.deleteOne({ name: "John" })

Explanation:
deleteOne() removes one matching document.

---

✅ Q7: Sort Data

Problem:
Sort students by age in descending order.

Solution:

db.students.find().sort({ age: -1 })

Explanation:
-1 = descending, 1 = ascending.

---

✅ Q8: Limit Results

Problem:
Show only 2 students.

Solution:

db.students.find().limit(2)

Explanation:
limit() restricts number of results.

🔵 Level 3: Advanced Exercises

✅ Q9: Design a Schema (Embedding vs Referencing)

Problem:
Design a schema for Users and Orders where each user can have many orders.

Solution:

// Users Collection
{
  _id: 1,
  name: "Amit"
}

// Orders Collection
{
  _id: 101,
  user_id: 1,
  product: "Laptop",
  price: 50000
}

Explanation:
Use referencing when data grows large. Avoid embedding too many orders inside a single document.

---

✅ Q10: Aggregation Query

Problem:
Find the average age of students.

Solution:

db.students.aggregate([
  {
    $group: {
      _id: null,
      averageAge: { $avg: "$age" }
    }
  }
])

Explanation:
$group is used for aggregation and $avg calculates average.

---

✅ Q11: Find Duplicate Data

Problem:
Find duplicate student names.

Solution:

db.students.aggregate([
  {
    $group: {
      _id: "$name",
      count: { $sum: 1 }
    }
  },
  {
    $match: {
      count: { $gt: 1 }
    }
  }
])

Explanation:
Groups data by name and filters duplicates using $match.

🚀 Bonus Challenge

Challenge:
Design a database for a blog system with Users, Posts, and Comments.

Which data will you embed?
Which data will you reference?
Why?

🎯 Final Thoughts

If you completed these exercises, you now understand:

CRUD operations (Create, Read, Update & Delete)
Filtering & sorting
Aggregation
Schema design basics

The best way to learn MongoDB is:
Practice → Build → Break → Fix → Repeat

📚 What to Learn Next

MongoDB with Python (PyMongo)
Indexing for performance
Real-world projects

💬 Your Turn:
Which question did you find most challenging? Let us know in the comments!

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