Array-contains queries in Firebase - Mini Project: Build & Apply

Using Array-Contains Queries in Firebase

📖 Scenario: You are building a simple app to manage a collection of books. Each book document in Firebase Firestore has a field called genres, which is an array of strings representing the genres the book belongs to.For example, a book might have genres: ['fiction', 'mystery'].

🎯 Goal: Learn how to query Firestore to find all books that belong to a specific genre using the array-contains query.

📋 What You'll Learn

Create a Firestore collection reference called books_ref pointing to the 'books' collection.

Create a variable called search_genre with the exact string value 'fiction'.

Write a Firestore query called query_ref that uses where with array-contains to find books where the genres array contains search_genre.

Add a final line to get the documents from query_ref using get().

💡 Why This Matters

🌍 Real World

Array-contains queries are useful when you want to find documents that have a specific value inside an array field, such as tags, categories, or genres.

💼 Career

Understanding how to query array fields in Firestore is important for building efficient and user-friendly apps that filter data based on user interests or categories.

1

Create Firestore collection reference

Create a Firestore collection reference called books_ref that points to the collection named 'books'.

Firebase

# Your code here

Need a hint?

Use firestore.collection('books') to get the collection reference.

2

Create search genre variable

Create a variable called search_genre and set it to the string 'fiction'.

Firebase

const books_ref = firestore.collection('books');
// Your code here

Need a hint?

Use const search_genre = 'fiction'; to create the variable.

3

Write array-contains query

Create a Firestore query called query_ref that uses books_ref.where with the field 'genres', the operator 'array-contains', and the value search_genre.

Firebase

const books_ref = firestore.collection('books');
const search_genre = 'fiction';
// Your code here

Need a hint?

Use books_ref.where('genres', 'array-contains', search_genre) to create the query.

4

Get documents from query

Add a line to get the documents from query_ref by calling get() and assign it to a variable called query_snapshot.

Firebase

const books_ref = firestore.collection('books');
const search_genre = 'fiction';
const query_ref = books_ref.where('genres', 'array-contains', search_genre);
// Your code here

Need a hint?

Use await query_ref.get() to get the documents.