MongoDB connection with mongodb driver in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this MongoDB connection code?

Consider the following Node.js code snippet using the mongodb driver to connect to a MongoDB server and list database names. What will be printed to the console?

Node.js

import { MongoClient } from 'mongodb';

async function listDatabases() {
  const client = new MongoClient('mongodb://localhost:27017');
  try {
    await client.connect();
    const databasesList = await client.db().admin().listDatabases();
    console.log(databasesList.databases.map(db => db.name));
  } finally {
    await client.close();
  }
}

listDatabases();

A An error because the connection string is missing credentials

B An array of database names like ['admin', 'local', 'test']

C An empty array [] because no databases exist

D A TypeError because listDatabases is not a function

💡 Hint

Think about what listDatabases() returns and what map(db => db.name) does.

The listDatabases() method returns an object with a databases array. Mapping over it extracts the names, so the console prints an array of database names.

📝 Syntax

intermediate

Which option correctly creates a MongoClient instance to connect to a MongoDB Atlas cluster?

You want to connect to a MongoDB Atlas cluster with the connection string mongodb+srv://user:[e-mail]. Which code snippet correctly creates the MongoClient instance?

A const client = new MongoClient('mongodb+srv://user:[e-mail]', { useNewUrlParser: true });

B const client = new MongoClient('mongodb://user:[e-mail]');

C const client = new MongoClient('mongodb+srv://user:[e-mail]', true);

D const client = new MongoClient('mongodb+srv://user:[e-mail]');

💡 Hint

Remember the correct URI scheme for Atlas and the constructor signature.

The mongodb+srv scheme is required for Atlas. The MongoClient constructor takes the connection string as the first argument. Options are optional and must be an object.

❓ optimization

advanced

How to optimize MongoDB connection reuse in a Node.js app?

You have a Node.js app that connects to MongoDB on every request, causing delays. Which approach best optimizes connection reuse?

A Create a single <code>MongoClient</code> instance and reuse it across requests

B Create a new <code>MongoClient</code> instance for each request and close it after

C Use <code>MongoClient.connect()</code> inside each request handler without closing

D Use a global variable to store the connection string and create clients as needed

💡 Hint

Think about connection overhead and resource management.

Creating and closing a client for each request is expensive. Reusing a single client instance improves performance and resource usage.

🔧 Debug

advanced

Why does this MongoDB connection code throw a timeout error?

Given this code snippet, why does it throw a timeout error when trying to connect?

import { MongoClient } from 'mongodb';

const client = new MongoClient('mongodb://invalidhost:27017');

async function run() {
  await client.connect();
  console.log('Connected');
}

run();

A The hostname 'invalidhost' does not resolve, causing connection timeout

B The connection string is missing username and password, causing timeout

C The port 27017 is blocked by firewall, causing timeout

D The MongoClient constructor is missing options, causing timeout

💡 Hint

Check if the hostname is reachable.

A non-existent hostname causes the driver to wait until the connection attempt times out.

🧠 Conceptual

expert

What is the role of the useUnifiedTopology option in MongoClient?

In older versions of the mongodb driver, the useUnifiedTopology option was recommended. What does enabling this option do?

A Forces the driver to use legacy connection methods for compatibility

B Disables connection pooling to reduce resource usage

C Enables the new unified topology layer that improves server discovery and monitoring

D Automatically retries failed operations without user intervention

💡 Hint

Think about how the driver manages connections and monitors servers.

The unified topology layer provides a more robust and consistent way to handle server discovery and monitoring, improving reliability.