Why compound queries narrow results in Firebase - See It in Action

Why compound queries narrow results

📖 Scenario: You are managing a small online bookstore database using Firebase Firestore. You want to find books that match multiple conditions to help customers find exactly what they want.

🎯 Goal: Build a Firebase Firestore query that uses compound conditions to narrow down the list of books based on genre and price.

📋 What You'll Learn

Create a collection of books with fields: title, genre, and price

Add a configuration variable for the maximum price filter

Write a compound query filtering books by genre and price

Complete the query by adding a limit to the number of results

💡 Why This Matters

🌍 Real World

Online stores often need to filter products by multiple conditions to help customers find exactly what they want quickly.

💼 Career

Understanding compound queries is essential for cloud developers working with databases to efficiently retrieve relevant data.

1

Create the initial books collection data

Create a variable called books that is an array of objects. Each object should have these exact fields and values: { title: 'Book A', genre: 'fiction', price: 10 }, { title: 'Book B', genre: 'fiction', price: 15 }, { title: 'Book C', genre: 'non-fiction', price: 20 }, { title: 'Book D', genre: 'fiction', price: 25 }.

Firebase

// Create the books array with the given objects
// Your code here

Need a hint?

Use const books = [ ... ] with the exact objects inside.

2

Add a maximum price filter variable

Create a variable called maxPrice and set it to 20 to filter books by price.

Firebase

const books = [
  { title: 'Book A', genre: 'fiction', price: 10 },
  { title: 'Book B', genre: 'fiction', price: 15 },
  { title: 'Book C', genre: 'non-fiction', price: 20 },
  { title: 'Book D', genre: 'fiction', price: 25 }
];

// Create maxPrice variable set to 20
// Your code here

Need a hint?

Use const maxPrice = 20; exactly.

3

Write a compound query filtering by genre and price

Create a variable called filteredBooks that filters books to include only those with genre equal to 'fiction' and price less than or equal to maxPrice. Use the filter method with a function that checks both conditions.

Firebase

const books = [
  { title: 'Book A', genre: 'fiction', price: 10 },
  { title: 'Book B', genre: 'fiction', price: 15 },
  { title: 'Book C', genre: 'non-fiction', price: 20 },
  { title: 'Book D', genre: 'fiction', price: 25 }
];

const maxPrice = 20;

// Filter books by genre 'fiction' and price <= maxPrice
// Your code here

Need a hint?

Use books.filter(book => book.genre === 'fiction' && book.price <= maxPrice).

4

Limit the number of results returned

Create a variable called limitedBooks that contains the first 2 books from filteredBooks. Use the slice method to get the first 2 items.

Firebase

const books = [
  { title: 'Book A', genre: 'fiction', price: 10 },
  { title: 'Book B', genre: 'fiction', price: 15 },
  { title: 'Book C', genre: 'non-fiction', price: 20 },
  { title: 'Book D', genre: 'fiction', price: 25 }
];

const maxPrice = 20;

const filteredBooks = books.filter(book => book.genre === 'fiction' && book.price <= maxPrice);

// Limit results to first 2 books
// Your code here

Need a hint?

Use filteredBooks.slice(0, 2) to get the first two books.