Lecture Notes Of Class 12: Introduction to MongoDB

 

Lecture Notes Of Class 12: Introduction to MongoDB

Objective:

• To understand MongoDB and its significance as a NoSQL database.
• To learn how to use MongoDB with Node.js for database operations.

---

What is MongoDB?

MongoDB is a NoSQL database that stores data in a flexible, JSON-like format known as BSON (Binary JSON). Unlike traditional relational databases (like MySQL), MongoDB does not rely on tables and rows but instead uses collections and documents.

Key Features:

1.  Schema-less Database: Flexible structure, allowing different fields in different documents of the same collection.

2.  Scalability: Easily scalable horizontally by adding more servers.

3.  High Performance: Optimized for large-scale applications.

4.  Rich Query Language: Supports a wide range of queries, including filtering, aggregation, and indexing.

5.  Cross-Platform: Works on multiple operating systems like Windows, Linux, and macOS.

---

MongoDB Terminology

1.  Database: A container for collections.

2.  Collection: Equivalent to a table in relational databases.

3.  Document: A record in a collection, represented in BSON.

4.  Field: A key-value pair in a document, similar to a column in a table.

Example of a Document:

json

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{

  "name": "John Doe",

  "age": 25,

  "skills": ["JavaScript", "Node.js", "MongoDB"]

}

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How MongoDB Differs from SQL Databases

Feature	SQL Databases	MongoDB
Structure	Tables and Rows	Collections and Documents
Schema	Fixed schema	Flexible schema
Scalability	Vertical	Horizontal
Query Language	SQL	MongoDB Query Language (MQL)

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Using MongoDB with Node.js

Step 1: Install and Set Up MongoDB

Option 1: Install MongoDB Locally

1.  Download MongoDB Community Server from MongoDB Download Center.

2.  Install MongoDB and start the MongoDB server using the following command:

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mongod

3.  Use the MongoDB shell to interact with the database:

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mongo

Option 2: Use MongoDB Atlas (Cloud-Based Solution)

1.  Sign up at MongoDB Atlas.

2.  Create a cluster and get the connection string (e.g., mongodb+srv://<username>:<password>@cluster.mongodb.net/<dbname>).

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Step 2: Install the Mongoose Package

Mongoose is an ODM (Object Data Modeling) library for MongoDB and Node.js that provides a structured way to interact with MongoDB.

1.  Open your Node.js project directory and install Mongoose:

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npm install mongoose

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Step 3: Connect Node.js to MongoDB

1.  Create a New File: index.js.

2.  Import and Connect Mongoose:

javascript

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const mongoose = require('mongoose');

 

// MongoDB connection string (replace `<username>`, `<password>`, and `<dbname>` with your details)

const uri = "mongodb+srv://<username>:<password>@cluster.mongodb.net/<dbname>";

 

mongoose.connect(uri, { useNewUrlParser: true, useUnifiedTopology: true })

  .then(() => console.log("MongoDB connected"))

  .catch(err => console.log("Error connecting to MongoDB:", err));

---

Step 4: Perform Basic Database Operations

1. Define a Schema and Model:
A schema defines the structure of a document in MongoDB.

javascript

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const Schema = mongoose.Schema;

 

// Define schema for a 'User' collection

const userSchema = new Schema({

  name: String,

  age: Number,

  email: String

});

 

// Create a model

const User = mongoose.model('User', userSchema);

2. Insert a Document:

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const newUser = new User({

  name: "Alice",

  age: 30,

  email: "alice@example.com"

});

 

newUser.save()

  .then(() => console.log("User added!"))

  .catch(err => console.log("Error:", err));

3. Retrieve Documents:

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User.find()

  .then(users => console.log("All Users:", users))

  .catch(err => console.log("Error:", err));

4. Update a Document:

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User.updateOne({ name: "Alice" }, { age: 31 })

  .then(() => console.log("User updated!"))

  .catch(err => console.log("Error:", err));

5. Delete a Document:

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User.deleteOne({ name: "Alice" })

  .then(() => console.log("User deleted!"))

  .catch(err => console.log("Error:", err));

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Lab Tasks

1.  Install MongoDB: Either locally or via MongoDB Atlas.

2.  Install Mongoose: Run npm install mongoose in your project folder.

3.  Connect Node.js to MongoDB: Use the connection string provided by your MongoDB setup.

4.  Perform Basic Operations:

o    Create a schema and model for a Student collection with fields like name, rollNumber, and department.

o    Insert, retrieve, update, and delete student records.

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Conclusion

In this session, we learned about:

• MongoDB as a NoSQL database.
• Installing and connecting MongoDB with Node.js.
• Using Mongoose for schema definition and basic CRUD operations.

With these skills, you can integrate MongoDB into your Node.js projects to build robust and scalable applications.

---

Assignment

1.  Create a new collection called Books with fields: title, author, and year. Perform CRUD operations on this collection.

2.  Explore MongoDB documentation to learn about advanced queries.

4o

You said:

Solutions: Create a new collection called Books with fields: title, author, and year. Perform CRUD operations on this collection. Explore MongoDB documentation to learn about advanced queries.

ChatGPT said:

ChatGPT

Solution: CRUD Operations on Books Collection

Below is a step-by-step solution for creating and managing a Books collection with fields title, author, and year.

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Step 1: Define Schema and Model for Books Collection

Create a books.js file or add the following code to your project:

javascript

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const mongoose = require('mongoose');

 

// Define the schema for the Books collection

const bookSchema = new mongoose.Schema({

  title: { type: String, required: true },

  author: { type: String, required: true },

  year: { type: Number, required: true },

});

 

// Create the model for the Books collection

const Book = mongoose.model('Book', bookSchema);

 

module.exports = Book;

---

Step 2: CRUD Operations

Below are examples of performing Create, Read, Update, and Delete operations.

1. Create a New Book

Add a new book to the Books collection:

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const Book = require('./books'); // Import the model

 

// Create a new book document

const newBook = new Book({

  title: "To Kill a Mockingbird",

  author: "Harper Lee",

  year: 1960,

});

 

// Save the document to the database

newBook.save()

  .then(() => console.log("Book added successfully!"))

  .catch(err => console.log("Error adding book:", err));

---

2. Read Books

a. Fetch All Books:
Retrieve all documents from the Books collection:

javascript

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Book.find()

  .then(books => console.log("All Books:", books))

  .catch(err => console.log("Error fetching books:", err));

b. Fetch Books by Author:
Retrieve books written by a specific author:

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Book.find({ author: "Harper Lee" })

  .then(books => console.log("Books by Harper Lee:", books))

  .catch(err => console.log("Error fetching books:", err));

---

3. Update a Book

Update the year of a book by its title:

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Book.updateOne({ title: "To Kill a Mockingbird" }, { year: 1961 })

  .then(() => console.log("Book updated successfully!"))

  .catch(err => console.log("Error updating book:", err));

---

4. Delete a Book

Delete a book by its title:

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Book.deleteOne({ title: "To Kill a Mockingbird" })

  .then(() => console.log("Book deleted successfully!"))

  .catch(err => console.log("Error deleting book:", err));

---

Advanced MongoDB Queries

1.  Sorting:
Sort books by year in descending order:

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Book.find().sort({ year: -1 })

  .then(books => console.log("Books sorted by year:", books))

  .catch(err => console.log("Error sorting books:", err));

2.  Pagination:
Retrieve books in pages (e.g., 5 books per page):

javascript

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const page = 1; // Current page

const limit = 5; // Books per page

 

Book.find()

  .skip((page - 1) * limit)

  .limit(limit)

  .then(books => console.log("Paginated books:", books))

  .catch(err => console.log("Error paginating books:", err));

3.  Aggregation:
Count the number of books published per author:

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Book.aggregate([

  { $group: { _id: "$author", totalBooks: { $sum: 1 } } }

])

  .then(result => console.log("Books per author:", result))

  .catch(err => console.log("Error aggregating books:", err));

---

Exploring MongoDB Documentation

The MongoDB official documentation is a rich resource for learning advanced features like indexing, aggregation pipelines, and geospatial queries.

Visit: MongoDB Documentation

---

Output Examples

1.  Create:
Output after adding a book:

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Book added successfully!

2.  Read:
Fetch all books:

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All Books: [

  { _id: 1, title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960 }

]

3.  Update:
Output after updating:

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Book updated successfully!

4.  Delete:
Output after deletion:

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Book deleted successfully!

This process helps manage the Books collection and explore MongoDB's advanced capabilities effectively.

4o

You said:

Write 10 assignments with solution and explanation in detail on above concept

ChatGPT said:

ChatGPT

10 Assignments on MongoDB and Node.js

Below are 10 assignments based on the above concept, each with detailed solutions and explanations to solidify understanding of MongoDB and Node.js integration.

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Assignment 1: Create a MongoDB Database

Task: Create a database named Library and verify its existence using MongoDB Compass or the MongoDB shell.

Solution:

In the MongoDB shell:

bash

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use Library

show dbs

Explanation:

• The use Library command switches to the Library database, creating it if it doesn't already exist.
• The show dbs command lists all databases, including Library if documents are added.

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Assignment 2: Create a Collection

Task: Create a collection named Books within the Library database.

Solution:

In the MongoDB shell:

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use Library

db.createCollection("Books")

show collections

Explanation:

• db.createCollection("Books") explicitly creates the Books collection.
• show collections lists all collections in the current database.

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Assignment 3: Insert a Document into a Collection

Task: Add a document with the fields title: "1984", author: "George Orwell", and year: 1949 into the Books collection.

Solution:

In the MongoDB shell:

bash

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db.Books.insertOne({

  title: "1984",

  author: "George Orwell",

  year: 1949

})

Explanation:

• insertOne adds a single document to the collection.
• This creates the Books collection if it doesn’t already exist.

---

Assignment 4: Retrieve All Documents from a Collection

Task: Retrieve all documents from the Books collection.

Solution:

In the MongoDB shell:

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db.Books.find()

Explanation:

• find() fetches all documents in the Books collection.
• The output is a JSON-like structure of stored documents.

---

Assignment 5: Find Documents with Specific Criteria

Task: Find all books authored by "George Orwell".

Solution:

In the MongoDB shell:

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db.Books.find({ author: "George Orwell" })

Explanation:

• The { author: "George Orwell" } query filters documents matching the specified author.

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Assignment 6: Update a Document

Task: Update the year of the book titled "1984" to 1950.

Solution:

In the MongoDB shell:

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db.Books.updateOne(

  { title: "1984" },

  { $set: { year: 1950 } }

)

Explanation:

• The $set operator modifies the year field of the matched document.
• updateOne ensures only the first matching document is updated.

---

Assignment 7: Delete a Document

Task: Delete the book with the title "1984" from the Books collection.

Solution:

In the MongoDB shell:

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db.Books.deleteOne({ title: "1984" })

Explanation:

• deleteOne removes the first document matching the query.

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Assignment 8: Use Aggregation

Task: Count the total number of books grouped by author.

Solution:

In the MongoDB shell:

bash

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db.Books.aggregate([

  { $group: { _id: "$author", totalBooks: { $sum: 1 } } }

])

Explanation:

• $group groups documents by the author field.
• $sum: 1 counts the number of books per author.

---

Assignment 9: Pagination

Task: Retrieve the first two books, sorted by year in descending order.

Solution:

In the MongoDB shell:

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db.Books.find().sort({ year: -1 }).limit(2)

Explanation:

• sort({ year: -1 }) arranges books in descending order of year.
• limit(2) fetches only the first two documents.

---

Assignment 10: Integrate MongoDB with Node.js

Task: Write a Node.js script to connect to the Library database, create a Books collection, and insert a new document.

Solution:

In Node.js:

javascript

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const mongoose = require('mongoose');

 

// Connect to MongoDB

mongoose.connect('mongodb://127.0.0.1:27017/Library', {

  useNewUrlParser: true,

  useUnifiedTopology: true,

})

  .then(() => console.log("Connected to MongoDB"))

  .catch(err => console.log("Error connecting to MongoDB:", err));

 

// Define schema and model

const bookSchema = new mongoose.Schema({

  title: String,

  author: String,

  year: Number,

});

const Book = mongoose.model('Book', bookSchema);

 

// Insert a document

const newBook = new Book({

  title: "Brave New World",

  author: "Aldous Huxley",

  year: 1932,

});

newBook.save()

  .then(() => console.log("Book added successfully!"))

  .catch(err => console.log("Error adding book:", err));

Explanation:

1.  mongoose.connect establishes a connection to the MongoDB database.

2.  Schema and Model: The schema defines the document structure, while the model interacts with the collection.

3.  Insert Document: The save() method adds a new document to the collection.

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These assignments guide students through understanding basic and advanced MongoDB operations and connecting MongoDB with Node.js. By solving them, students will gain hands-on experience with CRUD operations, aggregation, and database integration.

4o

You said:

write 50 MCQs for the concept above with explanation

ChatGPT said:

ChatGPT

50 MCQs on MongoDB and Node.js

Below are multiple-choice questions (MCQs) with explanations based on the concepts of MongoDB and Node.js. Each question tests understanding and practical knowledge.

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1. What is MongoDB?

A. A relational database
B. A NoSQL database
C. A flat-file database
D. A cloud-only database

Answer: B
Explanation: MongoDB is a NoSQL database designed for storing, querying, and managing document-oriented data.

---

2. Which data format does MongoDB use to store data?

A. XML
B. JSON
C. BSON
D. YAML

Answer: C
Explanation: MongoDB stores data in BSON (Binary JSON), which is a binary-encoded serialization of JSON-like documents.

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3. Which command is used to switch to a database in MongoDB?

A. use <database_name>
B. switch <database_name>
C. db <database_name>
D. open <database_name>

Answer: A
Explanation: The use <database_name> command is used to switch to a specific database in MongoDB.

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4. What is the default port for MongoDB?

A. 27017
B. 3306
C. 8080
D. 5432

Answer: A
Explanation: MongoDB uses port 27017 by default for database connections.

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5. In Node.js, which package is used to interact with MongoDB?

A. mongoose
B. mysql
C. pg
D. sequelize

Answer: A
Explanation: The mongoose package is commonly used to interact with MongoDB in Node.js.

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6. What does db.createCollection() do?

A. Deletes a collection
B. Creates a collection explicitly
C. Updates a collection
D. Lists collections

Answer: B
Explanation: The db.createCollection() command creates a new collection explicitly.

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7. How can you retrieve all documents in a collection?

A. db.collection.findAll()
B. db.collection.find()
C. db.collection.get()
D. db.collection.select()

Answer: B
Explanation: The find() method retrieves all documents in a collection.

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8. Which method is used to insert a single document?

A. insert()
B. insertOne()
C. insertDocument()
D. addDocument()

Answer: B
Explanation: The insertOne() method adds a single document to a collection.

---

9. What does mongoose.Schema do?

A. Connects to MongoDB
B. Defines the structure of a document
C. Creates a new database
D. Deletes a collection

Answer: B
Explanation: In Mongoose, Schema is used to define the structure and data types of documents.

---

10. Which of the following is a valid Mongoose schema definition?

A. { title: String, author: String, year: Number }
B. [ title, author, year ]
C. { "title": "String", "author": "String", "year": "Number" }
D. Schema(title, author, year)

Answer: A
Explanation: Mongoose schema definitions use JavaScript objects to specify fields and their types.

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11. How do you connect Node.js to MongoDB using Mongoose?

A. mongoose.connect('mongodb://localhost:27017/dbname')
B. db.connect('localhost:27017/dbname')
C. mongo.connect('localhost:27017/dbname')
D. mongoose.connect('localhost/dbname')

Answer: A
Explanation: The correct syntax for connecting Node.js to MongoDB is mongoose.connect().

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12. What is the output of db.collection.countDocuments()?

A. Total number of documents in a collection
B. All document details
C. Document with a specific field
D. Number of collections

Answer: A
Explanation: The countDocuments() method returns the total number of documents in a collection.

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13. How do you sort documents in descending order by a field?

A. .sort({ field: 1 })
B. .sort({ field: -1 })
C. .orderBy(field)
D. .desc(field)

Answer: B
Explanation: Using .sort({ field: -1 }) sorts documents in descending order based on the specified field.

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14. Which of the following is a MongoDB aggregation pipeline stage?

A. $sort
B. $delete
C. $truncate
D. $update

Answer: A
Explanation: $sort is an aggregation pipeline stage used to sort documents.

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15. What is the purpose of the $group stage in MongoDB aggregation?

A. Deletes grouped documents
B. Groups documents by a field
C. Updates grouped documents
D. Counts grouped documents

Answer: B
Explanation: $group groups documents based on a specified field and applies aggregation operations.

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16. How do you delete one document in MongoDB?

A. db.collection.removeOne()
B. db.collection.delete()
C. db.collection.deleteOne()
D. db.collection.remove()

Answer: C
Explanation: The deleteOne() method removes a single document matching the query criteria.

---

17. What is MongoDB Atlas?

A. A mobile app for MongoDB
B. A cloud-hosted MongoDB service
C. A command-line tool for MongoDB
D. An offline MongoDB client

Answer: B
Explanation: MongoDB Atlas is a cloud-hosted database service for managing MongoDB deployments.

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18. What is the purpose of new mongoose.Schema()?

A. Connects to MongoDB
B. Defines a schema for a collection
C. Deletes a document
D. Updates a document

Answer: B
Explanation: new mongoose.Schema() is used to define a schema for documents in a collection.

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19. Which operator is used to update a field in MongoDB?

A. $set
B. $update
C. $change
D. $modify

Answer: A
Explanation: The $set operator updates the value of a specific field.

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20. Which command lists all databases?

A. show dbs
B. list dbs
C. dbs()
D. display dbs

Answer: A
Explanation: The show dbs command lists all available databases in MongoDB.

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21. Which of the following is a NoSQL database type?

A. Document-oriented
B. Relational
C. Tabular
D. Hierarchical

Answer: A
Explanation: Document-oriented databases, like MongoDB, store data as documents.

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22. How do you check the current database in MongoDB?

A. current db
B. db.current()
C. db
D. show db

Answer: C
Explanation: Typing db in the MongoDB shell displays the current database.

---

---

If you'd like the remaining 28 questions, please let me know, and I'll continue!

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You said:

yes

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ChatGPT

23. Which method is used to insert multiple documents into a MongoDB collection?

A. insert()
B. insertMany()
C. bulkInsert()
D. addDocuments()

Answer: B
Explanation: The insertMany() method is used to insert multiple documents into a collection at once.

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24. What is the primary advantage of using MongoDB over a relational database?

A. Strong data typing
B. Horizontal scalability
C. Built-in joins
D. Fixed schema

Answer: B
Explanation: MongoDB's horizontal scalability makes it a popular choice for handling large datasets.

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25. Which method in Mongoose is used to create a new document?

A. save()
B. add()
C. store()
D. createDocument()

Answer: A
Explanation: The save() method is used in Mongoose to save a document to the database.

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26. How does MongoDB handle unstructured data?

A. By enforcing strict schemas
B. By supporting dynamic schemas
C. By converting to relational format
D. By rejecting unstructured data

Answer: B
Explanation: MongoDB supports dynamic schemas, allowing it to store unstructured data.

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27. Which of the following commands shows all collections in a database?

A. list collections
B. show collections
C. db.collections
D. display collections

Answer: B
Explanation: The show collections command lists all collections in the current database.

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28. What does the findOne() method return?

A. All documents in a collection
B. The first document that matches the query
C. The last document that matches the query
D. A count of matching documents

Answer: B
Explanation: The findOne() method returns the first document that matches the query criteria.

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29. What is a collection in MongoDB?

A. A single document
B. A group of databases
C. A group of documents
D. A table-like structure with fixed rows

Answer: C
Explanation: A collection is a group of related documents in MongoDB, similar to a table in relational databases.

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30. Which of the following is NOT a valid MongoDB data type?

A. String
B. Number
C. Boolean
D. ArrayBuffer

Answer: D
Explanation: ArrayBuffer is not a valid MongoDB data type. MongoDB supports types like String, Number, and Boolean.

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31. How do you create an index on a field in MongoDB?

A. db.collection.createIndex({ field: 1 })
B. db.collection.index({ field: 1 })
C. db.collection.addIndex({ field: 1 })
D. db.collection.indexField({ field: 1 })

Answer: A
Explanation: The createIndex() method creates an index on a specified field in a collection.

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32. What is the purpose of a primary key in MongoDB?

A. To ensure unique field values
B. To group related collections
C. To define relationships
D. To allow null values

Answer: A
Explanation: The _id field in MongoDB acts as the primary key and ensures each document has a unique identifier.

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33. How do you update multiple documents in MongoDB?

A. updateMany()
B. updateAll()
C. bulkUpdate()
D. updateDocuments()

Answer: A
Explanation: The updateMany() method is used to update multiple documents in a collection.

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34. What is the purpose of the $match stage in the aggregation pipeline?

A. To filter documents based on conditions
B. To delete documents
C. To join collections
D. To create indexes

Answer: A
Explanation: The $match stage filters documents based on specified conditions in the aggregation pipeline.

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35. Which command is used to delete a collection in MongoDB?

A. db.collection.deleteCollection()
B. db.collection.remove()
C. db.collection.drop()
D. db.collection.destroy()

Answer: C
Explanation: The drop() method deletes a collection from the database.

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36. What is the purpose of MongoDB Compass?

A. Command-line tool for MongoDB
B. Cloud service for hosting databases
C. GUI for managing MongoDB databases
D. Query optimizer

Answer: C
Explanation: MongoDB Compass is a GUI tool used for managing and visualizing MongoDB databases.

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37. Which method is used to close a database connection in Node.js?

A. mongoose.close()
B. mongoose.disconnect()
C. db.close()
D. db.disconnect()

Answer: B
Explanation: The mongoose.disconnect() method is used to close the database connection.

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38. How is the $or operator used in MongoDB?

A. Filters documents where at least one condition is true
B. Updates documents where conditions are true
C. Deletes documents matching multiple conditions
D. Joins two collections

Answer: A
Explanation: The $or operator filters documents where at least one of the provided conditions is true.

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39. How do you define a unique index in MongoDB?

A. db.collection.createIndex({ field: 1 }, { unique: true })
B. db.collection.addUniqueIndex({ field: 1 })
C. db.collection.setIndex({ field: 1 }, unique)
D. db.collection.uniqueIndex({ field: 1 })

Answer: A
Explanation: To create a unique index, use createIndex() with the unique: true option.

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40. What does the $push operator do?

A. Adds a value to an array field
B. Removes a value from an array
C. Updates a document field
D. Deletes an array field

Answer: A
Explanation: The $push operator appends a value to an array field in a document.

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41. How do you count the number of documents in a collection?

A. db.collection.count()
B. db.collection.countDocuments()
C. db.collection.documentCount()
D. db.collection.totalCount()

Answer: B
Explanation: The countDocuments() method is used to count the number of documents in a collection.

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42. Which Node.js event is triggered when the MongoDB connection is successful?

A. connected
B. open
C. ready
D. online

Answer: B
Explanation: The open event is triggered when the MongoDB connection is successfully established.

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43. What is a replica set in MongoDB?

A. A single database instance
B. A group of servers for redundancy
C. A way to join collections
D. A command for indexing

Answer: B
Explanation: A replica set is a group of MongoDB servers that provide redundancy and high availability.

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44. How do you filter documents where a field value is greater than 100?

A. { field: { $gt: 100 } }
B. { field: { $gte: 100 } }
C. { field: { $greater: 100 } }
D. { field: { >: 100 } }

Answer: A
Explanation: The $gt operator filters documents where the field value is greater than the specified value.

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45. What does the $lookup stage in aggregation do?

A. Deletes documents
B. Joins two collections
C. Updates documents
D. Sorts documents

Answer: B
Explanation: The $lookup stage performs a join operation between two collections.

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46. How do you delete all documents in a collection?

A. deleteMany({})
B. deleteAll()
C. removeDocuments()
D. truncate()

Answer: A
Explanation: The deleteMany({}) method removes all documents from a collection.

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47. What is the default write concern in MongoDB?

A. majority
B. 1
C. all
D. 0

Answer: B
Explanation: The default write concern in MongoDB acknowledges the write operation after the primary node writes the data.

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48. What does the _id field represent in MongoDB?

A. A user-defined primary key
B. A unique identifier for each document
C. The database name
D. The collection name

Answer: B
Explanation: The _id field is a unique identifier for every document in a MongoDB collection.

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49. Which operator is used to check if a field exists in a document?

A. $exists
B. $check
C. $fieldExists
D. $isField

Answer: A
Explanation: The $exists operator checks if a specified field exists in a document.

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