Projection for reducing data transfer in MongoDB - Mini Project: Build & Apply

Projection for Reducing Data Transfer in MongoDB

📖 Scenario: You work for a small online bookstore. The database has a collection called books with many details about each book, including title, author, year, price, and description. You want to show a list of books on the website but only need the title and author to reduce the amount of data sent from the database.

🎯 Goal: Build a MongoDB query that uses projection to return only the title and author fields from the books collection, excluding all other fields.

📋 What You'll Learn

Create a books collection with 3 documents containing title, author, year, price, and description fields.

Create a variable called projection that includes only title and author fields.

Write a query using find() on books with the projection to get only those fields.

Add a final command to convert the query result to an array.

💡 Why This Matters

🌍 Real World

Projection helps reduce the amount of data sent from the database to the application, making web pages load faster and saving bandwidth.

💼 Career

Database developers and backend engineers use projection to optimize queries and improve application performance.

1

Create the books collection with sample data

Create a variable called books and assign it an array with these 3 documents exactly: { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, price: 15.99, description: "A fantasy novel." }, { title: "1984", author: "George Orwell", year: 1949, price: 12.99, description: "A dystopian novel." }, { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, price: 14.99, description: "A novel about racial injustice." }

MongoDB

# Create the books array with 3 documents
# Your code here

Need a hint?

Use an array of objects with the exact fields and values given.

2

Create the projection variable to select only title and author

Create a variable called projection and set it to an object that includes title and author with value 1 to include them in the query result.

MongoDB

books = [
    { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, price: 15.99, description: "A fantasy novel." },
    { title: "1984", author: "George Orwell", year: 1949, price: 12.99, description: "A dystopian novel." },
    { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, price: 14.99, description: "A novel about racial injustice." }
]

# Create projection object to include only title and author
# Your code here

Need a hint?

Use 1 to include fields in MongoDB projection.

3

Write the query using find() with the projection

Write a query using db.books.find({}, projection) to get only the title and author fields from the books collection.

MongoDB

books = [
    { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, price: 15.99, description: "A fantasy novel." },
    { title: "1984", author: "George Orwell", year: 1949, price: 12.99, description: "A dystopian novel." },
    { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, price: 14.99, description: "A novel about racial injustice." }
]

projection = { title: 1, author: 1 }

# Write the query to find all books with projection
# Your code here

Need a hint?

Use empty filter {} to select all documents and pass projection as second argument.

4

Convert the query result to an array

Add .toArray() to the query to get the results as an array and assign it to a variable called result.

MongoDB

books = [
    { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, price: 15.99, description: "A fantasy novel." },
    { title: "1984", author: "George Orwell", year: 1949, price: 12.99, description: "A dystopian novel." },
    { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, price: 14.99, description: "A novel about racial injustice." }
]

projection = { title: 1, author: 1 }

query = db.books.find({}, projection)

# Convert query to array and assign to result
# Your code here

Need a hint?

Use .toArray() to get all documents from the cursor as an array.