Querying array elements directly in MongoDB - Mini Project: Build & Apply

Querying Array Elements Directly in MongoDB

📖 Scenario: You work at a bookstore that stores book information in a MongoDB collection. Each book document has a title and an array of reviews. Each review has a reviewer's name and a rating.You want to find books that have at least one review with a rating of 5.

🎯 Goal: Build a MongoDB query that finds books with at least one review having a rating of 5 by querying array elements directly.

📋 What You'll Learn

Create a collection named books with documents containing title and reviews array

Add a configuration variable targetRating set to 5

Write a query that finds books where any review's rating equals targetRating

Complete the query to return only the title and matching reviews elements

💡 Why This Matters

🌍 Real World

Many applications store lists of related data inside documents. Querying array elements directly helps find specific items quickly.

💼 Career

Database developers and backend engineers often write queries to filter nested array data in MongoDB for efficient data retrieval.

1

Create the books collection with sample data

Create a MongoDB collection called books and insert these exact documents: { title: "Book A", reviews: [{ reviewer: "Alice", rating: 4 }, { reviewer: "Bob", rating: 5 }] } and { title: "Book B", reviews: [{ reviewer: "Carol", rating: 3 }, { reviewer: "Dave", rating: 2 }] }.

MongoDB

// Insert the two book documents into the books collection
// Your code here

Need a hint?

Use db.books.insertMany() with an array of two objects as shown.

2

Set the targetRating variable

Create a variable called targetRating and set it to the number 5.

MongoDB

db.books.insertMany([
  { title: "Book A", reviews: [{ reviewer: "Alice", rating: 4 }, { reviewer: "Bob", rating: 5 }] },
  { title: "Book B", reviews: [{ reviewer: "Carol", rating: 3 }, { reviewer: "Dave", rating: 2 }] }
])

// Create targetRating variable and set it to 5
// Your code here

Need a hint?

Use const targetRating = 5 to create the variable.

3

Write the query to find books with a review rating equal to targetRating

Write a MongoDB query using db.books.find() that finds documents where the reviews array has at least one element with rating equal to targetRating. Use the query { "reviews.rating": targetRating }.

MongoDB

db.books.insertMany([
  { title: "Book A", reviews: [{ reviewer: "Alice", rating: 4 }, { reviewer: "Bob", rating: 5 }] },
  { title: "Book B", reviews: [{ reviewer: "Carol", rating: 3 }, { reviewer: "Dave", rating: 2 }] }
])

const targetRating = 5

// Write the query to find books with reviews.rating equal to targetRating
// Your code here

Need a hint?

Use dot notation "reviews.rating" in the query object.

4

Complete the query to return only title and matching reviews elements

Complete the query by calling db.books.find() with the query and a projection that returns only title and the matching reviews.$ element.

MongoDB

db.books.insertMany([
  { title: "Book A", reviews: [{ reviewer: "Alice", rating: 4 }, { reviewer: "Bob", rating: 5 }] },
  { title: "Book B", reviews: [{ reviewer: "Carol", rating: 3 }, { reviewer: "Dave", rating: 2 }] }
])

const targetRating = 5

const query = { "reviews.rating": targetRating }

// Complete the find() call with projection to return title and matching reviews element
// Your code here

Need a hint?

Use { title: 1, "reviews.$": 1 } as the projection to get only the title and the matched review.