Projection for selecting fields in MongoDB - Mini Project: Build & Apply

Projection for Selecting Fields in MongoDB

📖 Scenario: You are managing a small online bookstore database. The books collection contains documents with details about each book, including title, author, year published, genre, and price.You want to learn how to retrieve only specific information from the database to make your queries faster and easier to read.

🎯 Goal: Build a MongoDB query that uses projection to select only the title and author fields from the books collection.

📋 What You'll Learn

Create a books collection with 3 book documents having fields: title, author, year, genre, and price.

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

Write a MongoDB query using find() on books with the projection variable.

Add a final line to execute the query and store the results in a variable called selectedBooks.

💡 Why This Matters

🌍 Real World

Selecting only needed fields from a database makes queries faster and reduces data transfer, which is important for web apps and APIs.

💼 Career

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

1

Create the books collection with sample documents

Create a variable called books and assign it an array with exactly these 3 documents:
{ title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, genre: "Fantasy", price: 15 },
{ title: "1984", author: "George Orwell", year: 1949, genre: "Dystopian", price: 12 },
{ title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, genre: "Fiction", price: 10 }.

MongoDB

const books = [
  // Your code here
];

Need a hint?

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

2

Create the projection variable to select fields

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

MongoDB

const books = [
  { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, genre: "Fantasy", price: 15 },
  { title: "1984", author: "George Orwell", year: 1949, genre: "Dystopian", price: 12 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, genre: "Fiction", price: 10 }
];

// Your code here

Need a hint?

Use { title: 1, author: 1 } to include only these fields.

3

Write the MongoDB find() query with projection

Write a query using db.books.find() with an empty filter object {} and the projection variable as the second argument. Assign this query to a variable called query.

MongoDB

const books = [
  { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, genre: "Fantasy", price: 15 },
  { title: "1984", author: "George Orwell", year: 1949, genre: "Dystopian", price: 12 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, genre: "Fiction", price: 10 }
];

const projection = { title: 1, author: 1 };

// Your code here

Need a hint?

Use db.books.find({}, projection) to select only the fields in projection.

4

Execute the query and store the results

Add a line to execute the query by calling toArray() and assign the result to a variable called selectedBooks.

MongoDB

const books = [
  { title: "The Hobbit", author: "J.R.R. Tolkien", year: 1937, genre: "Fantasy", price: 15 },
  { title: "1984", author: "George Orwell", year: 1949, genre: "Dystopian", price: 12 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960, genre: "Fiction", price: 10 }
];

const projection = { title: 1, author: 1 };

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

// Your code here

Need a hint?

Use query.toArray() to get the results as an array.