Migrating from Realtime Database to Firestore in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Firestore Data Model Differences

When migrating from Realtime Database to Firestore, which of the following best describes a key difference in how data is structured?

A Firestore uses a flat JSON tree, while Realtime Database stores data in tables.

B Both Firestore and Realtime Database use the same JSON tree structure but with different security rules.

C Firestore stores data in documents and collections, while Realtime Database uses a large JSON tree.

D Realtime Database stores data in documents and collections, while Firestore uses a large JSON tree.

💡 Hint

Think about how Firestore organizes data compared to Realtime Database.

Firestore organizes data into documents and collections, which allows for more structured and scalable data storage. Realtime Database uses a single large JSON tree.

❓ Architecture

intermediate

Choosing Firestore Security Rules for Migrated Data

After migrating data from Realtime Database to Firestore, which security rule approach is recommended to maintain similar access control?

A Use Firestore rules that check document fields and user authentication to control access at the document level.

B Reuse Realtime Database rules directly in Firestore without changes.

C Disable all Firestore security rules temporarily to avoid access issues.

D Use Firestore rules only at the collection level without checking document fields.

💡 Hint

Consider how Firestore rules differ from Realtime Database rules in granularity.

Firestore security rules operate at the document level and can check fields and authentication to control access precisely. Realtime Database rules cannot be reused directly.

❓ Configuration

advanced

Firestore Query Behavior After Migration

Which Firestore query will correctly retrieve all documents from the 'users' collection where the 'age' field is greater than 25?

const usersRef = firestore.collection('users');
const query = ???;

A usersRef.get('age' > 25)

B usersRef.filter('age', '>', 25)

C usersRef.query('age' > 25)

D usersRef.where('age', '>', 25)

💡 Hint

Recall the Firestore method to filter documents by field values.

Firestore uses the where method to filter documents by field values. Other methods like filter or query do not exist.

❓ service_behavior

advanced

Handling Offline Support Differences

After migrating to Firestore, which statement correctly describes offline data behavior compared to Realtime Database?

A Firestore disables offline support by default and requires extra configuration to enable it.

B Realtime Database has built-in offline support, but Firestore does not support offline mode.

C Both Firestore and Realtime Database require manual caching for offline support.

D Firestore provides built-in offline support with automatic synchronization when online, unlike Realtime Database which requires manual handling.

💡 Hint

Think about how Firestore manages offline data synchronization.

Firestore disables offline support by default (on web SDK) and requires extra configuration such as enablePersistence() to enable it, while Realtime Database has built-in offline support automatically.

❓ security

expert

Preventing Unauthorized Data Access Post-Migration

After migrating to Firestore, you want to ensure users can only read their own profile documents stored in the 'users' collection where document IDs match user IDs. Which Firestore security rule snippet correctly enforces this?

service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow read: ???;
    }
  }
}

A request.auth.uid == 'admin'

B request.auth != null && request.auth.uid == userId

C request.auth.uid != null

D true

💡 Hint

Consider how to match authenticated user ID with document ID.

The rule allows read only if the user is authenticated and their UID matches the document ID, preventing access to other users' data.