Document ID strategies in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Firebase Document ID uniqueness

Which statement best describes how Firebase ensures document ID uniqueness within a collection?

A Firebase automatically generates a unique ID for each document if none is provided, ensuring no duplicates within the collection.

B Firebase allows duplicate document IDs within the same collection but prevents duplicates across different collections.

C Firebase requires the user to manually check and prevent duplicate document IDs before adding documents.

D Firebase uses timestamps as document IDs to guarantee uniqueness across all collections.

💡 Hint

Think about how Firebase handles document creation when no ID is specified.

Firebase generates a unique 20-character ID automatically for documents without a specified ID, ensuring uniqueness within the collection.

❓ Architecture

intermediate

Choosing document ID strategy for user profiles

You want to store user profiles in Firebase Firestore. Which document ID strategy is best to ensure easy retrieval and uniqueness?

A Use the user's email address as the document ID.

B Use Firebase's auto-generated IDs for each user profile document.

C Use the user's unique authentication UID as the document ID.

D Use a random UUID generated on the client side as the document ID.

💡 Hint

Consider which ID is guaranteed unique and consistent for each user.

The user's authentication UID is unique and consistent, making it ideal as a document ID for user profiles.

❓ security

advanced

Security risks of predictable document IDs

What is a major security risk when using predictable document IDs like sequential numbers in Firebase Firestore?

A It causes Firebase to reject writes due to ID conflicts.

B It allows attackers to guess document IDs and access unauthorized data if security rules are not strict.

C It increases Firestore costs because predictable IDs require more storage.

D It slows down queries because Firestore indexes sequential IDs less efficiently.

💡 Hint

Think about what happens if someone can guess document IDs.

Predictable IDs can be guessed by attackers, potentially exposing data if security rules are weak.

✅ Best Practice

advanced

Best practice for document ID length and readability

Which document ID strategy balances uniqueness, readability, and performance in Firebase Firestore?

A Use short, human-readable IDs like usernames without extra uniqueness checks.

B Use a combination of a short prefix and a timestamp to create IDs.

C Use long UUIDs (36 characters) for all documents regardless of use case.

D Use Firebase's auto-generated 20-character IDs for all documents.

💡 Hint

Consider what Firebase recommends for most use cases.

Firebase's auto-generated IDs are designed to be unique, efficient, and not too long, making them a good default choice.

❓ service_behavior

expert

Effect of document ID choice on Firestore query performance

How does choosing sequential numeric document IDs affect Firestore query performance compared to using Firebase's auto-generated IDs?

A Sequential numeric IDs cause hotspots in Firestore, reducing write performance and increasing latency.

B Sequential numeric IDs improve query speed because documents are stored in order.

C There is no difference in performance between sequential numeric IDs and auto-generated IDs.

D Auto-generated IDs cause hotspots because they are random and scattered.

💡 Hint

Think about how Firestore stores documents and handles writes.

Sequential IDs cause Firestore to write to the same storage location repeatedly, creating hotspots and slowing performance.