Firestore queries and indexes in GCP - Mini Project: Build & Apply

Firestore Queries and Indexes

📖 Scenario: You are building a simple app to manage a library's book collection using Google Firestore. You want to organize the data and run queries efficiently.

🎯 Goal: Create a Firestore collection with book data, add a configuration for filtering, write a query to find books by a specific author, and finally configure a composite index to support the query.

📋 What You'll Learn

Create a Firestore collection named books with specific book documents

Add a variable to filter books by the author "Jane Austen"

Write a Firestore query to get books where author equals the filter variable

Add a composite index configuration for author and publishedYear

💡 Why This Matters

🌍 Real World

Firestore is used to store and query data in many apps. Knowing how to structure data and indexes helps apps run fast and scale well.

💼 Career

Cloud engineers and developers often configure Firestore queries and indexes to optimize app performance and cost.

1

Create the Firestore collection with book documents

Create a Firestore collection named books with these exact documents: {"title": "Pride and Prejudice", "author": "Jane Austen", "publishedYear": 1813}, {"title": "Emma", "author": "Jane Austen", "publishedYear": 1815}, and {"title": "1984", "author": "George Orwell", "publishedYear": 1949}.

GCP

# Create the Firestore collection 'books' with the specified documents
# Your code here

Hint

Use a list named books with dictionaries for each book.

2

Add a filter variable for author

Create a variable called author_filter and set it to the string "Jane Austen" to filter books by this author.

GCP

books = [
    {"title": "Pride and Prejudice", "author": "Jane Austen", "publishedYear": 1813},
    {"title": "Emma", "author": "Jane Austen", "publishedYear": 1815},
    {"title": "1984", "author": "George Orwell", "publishedYear": 1949}
]
# Create the variable 'author_filter' with value 'Jane Austen'
# Your code here

Hint

Assign the exact string "Jane Austen" to author_filter.

3

Write a Firestore query to get books by the author filter

Write a Firestore query named query that filters the books collection where the author field equals the variable author_filter.

GCP

books = [
    {"title": "Pride and Prejudice", "author": "Jane Austen", "publishedYear": 1813},
    {"title": "Emma", "author": "Jane Austen", "publishedYear": 1815},
    {"title": "1984", "author": "George Orwell", "publishedYear": 1949}
]
author_filter = "Jane Austen"
# Write a query filtering books where author equals author_filter
# Your code here

Hint

Use a list comprehension named query to filter books by author_filter.

4

Add a composite index configuration for author and publishedYear

Add a Firestore composite index configuration named composite_index as a dictionary with collectionId set to "books", and fields as a list of dictionaries for author ascending and publishedYear descending.

GCP

books = [
    {"title": "Pride and Prejudice", "author": "Jane Austen", "publishedYear": 1813},
    {"title": "Emma", "author": "Jane Austen", "publishedYear": 1815},
    {"title": "1984", "author": "George Orwell", "publishedYear": 1949}
]
author_filter = "Jane Austen"
query = [book for book in books if book["author"] == author_filter]
# Add the composite index configuration dictionary named 'composite_index'
# Your code here

Hint

Define composite_index as a dictionary with the required keys and list of fields.

Practice

1. What is the main purpose of indexes in Firestore queries?

easy

A. To make queries faster and more efficient

B. To store large files like images

C. To backup data automatically

D. To encrypt data for security

Solution

1. Step 1: Understand what indexes do in Firestore

   Indexes help Firestore find data quickly without scanning all documents.

2. Step 2: Relate indexes to query performance

   By using indexes, queries run faster and use less resources.

3. Final Answer:

   To make queries faster and more efficient -> Option A

4. Quick Check:

   Indexes speed up queries = D [OK]

Hint: Indexes speed up data search in Firestore queries [OK]

Common Mistakes:

• Thinking indexes store files
• Confusing indexes with backups
• Assuming indexes encrypt data

2. Which of the following is the correct syntax to create a simple Firestore query filtering by a field age equal to 30?

easy

A. db.collection('users').filter('age', '=', 30)

B. db.collection('users').where('age', '==', 30)

C. db.collection('users').query('age' == 30)

D. db.collection('users').find('age', 30)

Solution

1. Step 1: Recall Firestore query syntax

   Firestore uses where(field, operator, value) to filter data.

2. Step 2: Match syntax with options

   db.collection('users').where('age', '==', 30) uses where('age', '==', 30), which is correct syntax.

3. Final Answer:

   db.collection('users').where('age', '==', 30) -> Option B

4. Quick Check:

   Correct Firestore filter syntax = B [OK]

Hint: Use .where(field, '==', value) for filtering in Firestore [OK]

Common Mistakes:

• Using .filter instead of .where
• Using == inside query string
• Using .find which is not Firestore syntax

3. Given this Firestore query:

db.collection('orders').where('status', '==', 'shipped').orderBy('date', 'desc')

What must you do to avoid an error when running this query?

medium

A. Remove the orderBy clause

B. Create a single-field index on date only

C. No index needed, Firestore handles it automatically

D. Create a composite index on status and date

Solution

1. Step 1: Understand query with multiple filters and sorting

   This query filters by status and sorts by date.

2. Step 2: Know Firestore index requirements

   Firestore requires a composite index for queries with multiple filters or sorting on different fields.

3. Final Answer:

   Create a composite index on status and date -> Option D

4. Quick Check:

   Composite index needed for multiple filters + orderBy = A [OK]

Hint: Use composite indexes for queries with filters and sorting [OK]

Common Mistakes:

• Assuming single-field index is enough
• Thinking Firestore auto-creates all indexes
• Removing orderBy to fix error

4. You wrote this Firestore query:

db.collection('products').where('price', '>', 100).orderBy('name')

But it gives an error about missing index. What is the best fix?

medium

A. Change price filter to ==

B. Remove the orderBy clause

C. Create a composite index on price (ascending) and name (ascending)

D. Create a single-field index on name only

Solution

1. Step 1: Identify query components causing index error

   The query filters by price > 100 and orders by name.

2. Step 2: Understand Firestore index needs for range filter + orderBy

   Firestore requires a composite index on both fields with correct sort order.

3. Final Answer:

   Create a composite index on price (ascending) and name (ascending) -> Option C

4. Quick Check:

   Composite index needed for range filter + orderBy = C [OK]

Hint: Create composite index matching filter and orderBy fields [OK]

Common Mistakes:

• Removing orderBy instead of indexing
• Changing filter operator incorrectly
• Creating only single-field index

5. You want to query a Firestore collection events to find documents where type is 'conference' and attendees is greater than 100, sorted by date ascending. Which index should you create to support this query?

hard

A. Composite index on type (ascending), attendees (ascending), and date (ascending)

B. Single-field index on date only

C. Composite index on type (descending) and date (ascending)

D. No index needed, Firestore supports this query by default

Solution

1. Step 1: Analyze query filters and sorting

   The query filters by type == 'conference' and attendees > 100, and sorts by date ascending.

2. Step 2: Determine required index type

   Multiple filters plus sorting require a composite index including all these fields with correct order.

3. Final Answer:

   Composite index on type (ascending), attendees (ascending), and date (ascending) -> Option A

4. Quick Check:

   Composite index covers all filters and orderBy fields = A [OK]

Hint: Include all filter and orderBy fields in composite index [OK]

Common Mistakes:

• Creating only single-field index
• Using wrong sort order in index
• Assuming no index needed