MongoDB Concepts

🚀 Mastering MongoDB Concepts for Web Technologies

---

MongoDB is the backbone of MERN Stack applications, and understanding it is crucial for building scalable applications and acing interviews. Here’s a quick guide covering all essential concepts! 👇

🔹 1. MongoDB Basics

✔ NoSQL Database – Stores data in JSON-like BSON format.

✔ Collections & Documents – Similar to SQL tables & rows, but flexible.

🔹 2. CRUD Operations

✔ Create – db.users.insertOne({ name: "Alice" })

✔ Read – db.users.find({ age: { $gt: 20 } })

✔ Update – db.users.updateOne({ name: "Alice" }, { $set: { age: 30 } })

✔ Delete – db.users.deleteOne({ name: "Alice" })

🔹 3. Indexing for Performance

✔ Speed up queries using indexes:

  db.users.createIndex({ email: 1 });

🔹 4. Aggregation Framework

✔ Used for data analytics & reporting.

✔ Example: Count users by age

  db.users.aggregate([{ $group: { _id: "$age", count: { $sum: 1 } } }]);

🔹 5. Relationships: Embed vs. Reference

✔ Embed: Store related data in the same document (faster reads).

✔ Reference: Store ObjectIDs to avoid redundancy (normalized).

🔹 6. Transactions for Atomic Operations

✔ Use Mongoose transactions when updating multiple documents:

  const session = await mongoose.startSession();
  session.startTransaction();
  try {
    await User.updateOne({ _id: userId }, { balance: 100 }, { session });
    await session.commitTransaction();
  } catch (err) {
    await session.abortTransaction();
  } finally {
    session.endSession();
  }

🔹 7. MongoDB in MERN Stack

✔ Connect MongoDB to Node.js

  mongoose.connect("mongodb://localhost:27017/myDB");

✔ Build APIs with Express.js

  app.get("/users", async (req, res) => {
    const users = await User.find();
    res.json(users);
  });

🔹 8. MongoDB Optimization & Best Practices

✅ Use Indexes for faster queries.

✅ Use Aggregation for analytics and reporting.
✅ Use Projection to fetch only required fields.

✅ Use Pagination with .limit() and .skip().

✅ Choose between Embedding vs. Referencing wisely.

🔥 Common Interview Questions

🔹 How does MongoDB differ from SQL?

🔹 What is the use of indexing in MongoDB?

🔹 How would you design a scalable database in MongoDB?

🔹 How do transactions work in MongoDB?

---

💬 Have any doubts? Drop them in the comments! Let's discuss. 👇