Combining logical and comparison operators in MongoDB - Mini Project: Build & Apply

Combining Logical and Comparison Operators in MongoDB Queries

📖 Scenario: You are managing a small online bookstore database. You want to find books that meet certain conditions to help with marketing and stock decisions.

🎯 Goal: Build a MongoDB query that uses both logical and comparison operators to find books that are either priced below $20 and have more than 50 copies in stock, or are authored by 'Jane Austen'.

📋 What You'll Learn

Create a collection named books with specific book documents.

Add a variable priceLimit set to 20.

Write a MongoDB query using $or, $and, $lt, $gt, and $eq operators.

Complete the query to find books matching the conditions described.

💡 Why This Matters

🌍 Real World

Filtering products or items in a database based on multiple conditions is common in e-commerce, inventory management, and reporting.

💼 Career

Knowing how to combine logical and comparison operators in queries is essential for database developers, data analysts, and backend engineers.

1

Create the books collection with sample documents

Create a MongoDB collection called books and insert these exact documents: { title: 'Pride and Prejudice', author: 'Jane Austen', price: 15, stock: 30 }, { title: '1984', author: 'George Orwell', price: 18, stock: 60 }, { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', price: 22, stock: 80 }, { title: 'Emma', author: 'Jane Austen', price: 25, stock: 40 }.

MongoDB

// Insert the specified documents into the books collection
// Your code here

Need a hint?

Use db.books.insertMany([...]) with the exact documents inside the array.

2

Set the price limit variable

Create a variable called priceLimit and set it to the number 20.

MongoDB

db.books.insertMany([
  { title: 'Pride and Prejudice', author: 'Jane Austen', price: 15, stock: 30 },
  { title: '1984', author: 'George Orwell', price: 18, stock: 60 },
  { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', price: 22, stock: 80 },
  { title: 'Emma', author: 'Jane Austen', price: 25, stock: 40 }
])

// Create priceLimit variable and set to 20
// Your code here

Need a hint?

Use const priceLimit = 20; to create the variable.

3

Write the MongoDB query with logical and comparison operators

Write a MongoDB query called query that uses $or with two conditions: one is an $and combining price less than priceLimit and stock greater than 50, the other is author equal to 'Jane Austen'.

MongoDB

db.books.insertMany([
  { title: 'Pride and Prejudice', author: 'Jane Austen', price: 15, stock: 30 },
  { title: '1984', author: 'George Orwell', price: 18, stock: 60 },
  { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', price: 22, stock: 80 },
  { title: 'Emma', author: 'Jane Austen', price: 25, stock: 40 }
])

const priceLimit = 20;

// Write the query using $or, $and, $lt, $gt, and $eq
// Your code here

Need a hint?

Use $or with an array containing an $and condition and an $eq condition for author.

4

Complete the query by running it on the books collection

Add a line to run db.books.find(query) to get the matching books.

MongoDB

db.books.insertMany([
  { title: 'Pride and Prejudice', author: 'Jane Austen', price: 15, stock: 30 },
  { title: '1984', author: 'George Orwell', price: 18, stock: 60 },
  { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', price: 22, stock: 80 },
  { title: 'Emma', author: 'Jane Austen', price: 25, stock: 40 }
])

const priceLimit = 20;

const query = {
  $or: [
    { $and: [ { price: { $lt: priceLimit } }, { stock: { $gt: 50 } } ] },
    { author: { $eq: 'Jane Austen' } }
  ]
};

// Run the query on the books collection
// Your code here

Need a hint?

Use db.books.find(query); to run the query.