MongoDB connection with mongodb driver in Node.js - Performance & Optimization

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Practice

1. What is the main purpose of using MongoClient from the mongodb package in Node.js?

easy

A. To start a web server

B. To create a new database schema

C. To connect to a MongoDB database server

D. To run SQL queries on MongoDB

Solution

1. Step 1: Understand MongoClient's role

   MongoClient is a class used to establish a connection to a MongoDB server from Node.js.

2. Step 2: Identify the correct purpose

   It does not create schemas or run SQL queries; it only manages connections to MongoDB.

3. Final Answer:

   To connect to a MongoDB database server -> Option C

4. Quick Check:

   MongoClient connects to MongoDB [OK]

Hint: MongoClient is for connecting to MongoDB servers [OK]

Common Mistakes:

• Confusing MongoClient with schema creation tools
• Thinking MongoClient runs SQL queries
• Assuming MongoClient starts web servers

2. Which of the following is the correct way to import MongoClient from the mongodb package in Node.js?

easy

A. const { MongoClient } = require('mongodb');

B. import MongoClient from 'mongodb';

C. const MongoClient = require('mongodb');

D. import { MongoClient } from 'mongodb';

Solution

1. Step 1: Identify Node.js import syntax

   In Node.js with CommonJS, destructuring import uses const { MongoClient } = require('mongodb');.

2. Step 2: Check other options

   const MongoClient = require('mongodb'); imports the entire module object, not the MongoClient class; import MongoClient from 'mongodb'; is ES module default import (incorrect here); import { MongoClient } from 'mongodb'; is ES module named import (valid only in ES modules).

3. Final Answer:

   const { MongoClient } = require('mongodb'); -> Option A

4. Quick Check:

   Destructured require syntax = const { MongoClient } = require('mongodb'); [OK]

Hint: Use destructuring with require for MongoClient in Node.js [OK]

Common Mistakes:

• Using default import syntax in CommonJS
• Requiring the module without accessing .MongoClient
• Mixing ES module and CommonJS syntax

3. What will be the output of the following code snippet if the MongoDB URI is correct and the connection is successful?

const { MongoClient } = require('mongodb');
async function run() {
  const client = new MongoClient('mongodb://localhost:27017');
  await client.connect();
  console.log('Connected successfully to server');
  await client.close();
}
run();

medium

A. Error: MongoClient is not defined

B. No output

C. SyntaxError: await is only valid in async function

D. Connected successfully to server

Solution

1. Step 1: Analyze the async function and connection

   The function run is async, creates a MongoClient, connects, logs success, then closes.

2. Step 2: Check for errors or output

   Since URI is correct and await is used properly inside async function, it logs the success message.

3. Final Answer:

   Connected successfully to server -> Option D

4. Quick Check:

   Successful connect logs message [OK]

Hint: Async function with await logs success message [OK]

Common Mistakes:

• Using await outside async function
• Not calling client.connect() before logging
• Forgetting to close the client

4. Identify the error in the following code snippet that tries to connect to MongoDB:

const { MongoClient } = require('mongodb');
const client = new MongoClient('mongodb://localhost:27017');
client.connect();
console.log('Connected');
client.close();

medium

A. Incorrect MongoDB URI format

B. Missing async/await for connect and close methods

C. MongoClient is not imported correctly

D. console.log syntax error

Solution

1. Step 1: Check usage of connect and close

   Both connect() and close() return promises and must be awaited or handled asynchronously.

2. Step 2: Identify missing async/await

   The code calls these methods without await or then, so connection may not complete before logging or closing.

3. Final Answer:

   Missing async/await for connect and close methods -> Option B

4. Quick Check:

   Async methods need await [OK]

Hint: Always await connect() and close() in async functions [OK]

Common Mistakes:

• Calling async methods without await
• Assuming connect() is synchronous
• Not wrapping calls in async function

5. You want to connect to a MongoDB server using the mongodb driver in Node.js and perform a simple query to find all documents in the users collection. Which of the following code snippets correctly connects, queries, and closes the connection?

hard

A. const { MongoClient } = require('mongodb');
async function run() {
const client = new MongoClient('mongodb://localhost:27017');
await client.connect();
const db = client.db('testdb');
const users = await db.collection('users').find().toArray();
console.log(users);
await client.close();
}
run();

B. const { MongoClient } = require('mongodb');
const client = new MongoClient('mongodb://localhost:27017');
const db = client.db('testdb');
const users = db.collection('users').find();
console.log(users);
client.close();

C. import { MongoClient } from 'mongodb';
const client = new MongoClient('mongodb://localhost:27017');
await client.connect();
const users = client.db('testdb').collection('users').find().toArray();
console.log(users);
await client.close();

D. const MongoClient = require('mongodb');
const client = new MongoClient('mongodb://localhost:27017');
client.connect();
const users = client.db('testdb').collection('users').find().toArray();
console.log(users);
client.close();

Solution

1. Step 1: Check for proper async/await usage

   const { MongoClient } = require('mongodb'); async function run() { const client = new MongoClient('mongodb://localhost:27017'); await client.connect(); const db = client.db('testdb'); const users = await db.collection('users').find().toArray(); console.log(users); await client.close(); } run(); uses async function with await for connect, query, and close, ensuring proper sequence.

2. Step 2: Validate correct import and method calls

   const { MongoClient } = require('mongodb'); async function run() { const client = new MongoClient('mongodb://localhost:27017'); await client.connect(); const db = client.db('testdb'); const users = await db.collection('users').find().toArray(); console.log(users); await client.close(); } run(); correctly imports MongoClient, connects, queries with toArray(), logs, and closes connection.

3. Final Answer:

   Uses destructured import, async function, await connect(), find().toArray(), await close() -> Option A

4. Quick Check:

   Async connect, query, close with await = const { MongoClient } = require('mongodb'); async function run() { const client = new MongoClient('mongodb://localhost:27017'); await client.connect(); const db = client.db('testdb'); const users = await db.collection('users').find().toArray(); console.log(users); await client.close(); } run(); [OK]

Hint: Use async/await for connect, query, and close in sequence [OK]

Common Mistakes:

• Not awaiting connect or query results
• Using incorrect import syntax
• Calling methods without async context