Realtime Database vs Firestore decision in Firebase - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize a Firestore database instance.

Firebase

const db = firebase.firestore().[1]();

Drag options to blanks, or click blank then click option'

Asettings

Bdoc

Cget

Dcollection

Attempts:

3 left

💡 Hint

Common Mistakes

Using collection() or doc() instead of settings() to configure Firestore.

The settings() method is used to configure Firestore settings after initialization.

2fill in blank

medium

Complete the code to listen for realtime updates in Realtime Database.

Firebase

database.ref('messages').[1](snapshot => { console.log(snapshot.val()); });

Drag options to blanks, or click blank then click option'

Aonce

Bget

Con

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using once() which only fetches data once instead of listening continuously.

The on() method listens continuously for data changes in Realtime Database.

3fill in blank

hard

Fix the error in Firestore query to get documents where age is greater than 18.

Firebase

db.collection('users').where('age', '[1]', 18).get().then(snapshot => { /* handle data */ });

Drag options to blanks, or click blank then click option'

A>

B==

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which only matches exact age 18.

Using '<=' or '<' which filter younger users.

The where clause uses '>' to filter documents with age greater than 18.

4fill in blank

hard

Fill both blanks to write a Firestore query that orders users by name and limits to 5 results.

Firebase

db.collection('users').[1]('name').[2](5).get();

Drag options to blanks, or click blank then click option'

AorderBy

Blimit

Cwhere

DstartAt

Attempts:

3 left

💡 Hint

Common Mistakes

Using where instead of orderBy for sorting.

Using startAt instead of limit to restrict results.

orderBy('name') sorts the results by name, and limit(5) restricts to 5 documents.

5fill in blank

hard

Fill all three blanks to write Realtime Database code that updates user age, sets a listener, and removes a user.

Firebase

database.ref('users/[1]').[2]({ age: 30 });
database.ref('users').[3](snapshot => { console.log(snapshot.val()); });
database.ref('users/[1]').remove();

Drag options to blanks, or click blank then click option'

Auser123

Bupdate

Con

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using set() instead of update() which overwrites data.

Using once() instead of on() for listening.

We update user 'user123' with update(), listen for changes with on(), and remove the same user.

Practice

1. Which Firebase database is best suited for simple real-time syncing of data as a JSON tree?

easy

A. Realtime Database

B. Firestore

C. Cloud Storage

D. Firebase Hosting

Solution

1. Step 1: Understand data structure of Realtime Database

   Realtime Database stores data as a JSON tree, which is simple and fast for syncing.

2. Step 2: Compare with Firestore

   Firestore uses collections and documents, better for complex queries but not just simple JSON tree syncing.

3. Final Answer:

   Realtime Database -> Option A

4. Quick Check:

   Simple JSON tree sync = Realtime Database [OK]

Hint: Simple JSON tree and fast sync? Choose Realtime Database [OK]

Common Mistakes:

• Confusing Firestore with Realtime Database
• Choosing Cloud Storage for database needs
• Thinking Firebase Hosting stores data

2. Which syntax correctly references a document in Firestore?

easy

A. db.store('users').document('user1')

B. db.collection('users').doc('user1')

C. db.get('users/user1')

D. db.ref('users/user1')

Solution

1. Step 1: Recall Firestore document reference syntax

   Firestore uses collection().doc() to reference documents.

2. Step 2: Identify incorrect options

   db.ref() is Realtime Database syntax; db.get() and db.store() are invalid here.

3. Final Answer:

   db.collection('users').doc('user1') -> Option B

4. Quick Check:

   Firestore document ref = collection().doc() [OK]

Hint: Firestore uses collection().doc() syntax [OK]

Common Mistakes:

• Using Realtime Database syntax for Firestore
• Mixing method names like get() or store()
• Confusing document and collection references

3. Given this Firestore query code, what will be the output if the 'users' collection has documents with ages 20, 25, and 30?

db.collection('users').where('age', '>', 22).get().then(snapshot => {
  let result = [];
  snapshot.forEach(doc => result.push(doc.data().age));
  console.log(result);
});

medium

A. [25, 30]

B. [20, 25, 30]

C. [22, 25]

D. []

Solution

1. Step 1: Understand the query condition

   The query filters users where age is greater than 22, so ages 25 and 30 qualify.

2. Step 2: Determine the output array

   The code collects ages from matching documents, so output is [25, 30].

3. Final Answer:

   [25, 30] -> Option A

4. Quick Check:

   age > 22 = [25, 30] [OK]

Hint: Filter > 22 excludes 20, includes 25 and 30 [OK]

Common Mistakes:

• Including 20 which is not > 22
• Confusing >= with > operator
• Assuming empty result without checking data

4. You wrote this Realtime Database code but it throws an error:

firebase.database().collection('users').doc('user1').get()

What is the main issue?

medium

A. Missing authentication before accessing database

B. The get() method is asynchronous and needs await

C. Realtime Database does not have collection() or doc() methods

D. The database URL is not specified

Solution

1. Step 1: Identify API mismatch

   Realtime Database uses ref() instead of collection() and doc(), which are Firestore methods.

2. Step 2: Confirm correct method usage

   Using collection() and doc() on Realtime Database causes error because those methods don't exist there.

3. Final Answer:

   Realtime Database does not have collection() or doc() methods -> Option C

4. Quick Check:

   Realtime DB uses ref(), not collection()/doc() [OK]

Hint: Realtime DB uses ref(), not collection() or doc() [OK]

Common Mistakes:

• Assuming get() needs await causes confusion
• Blaming authentication without checking API
• Thinking database URL causes this syntax error

5. You need to build a chat app that requires fast real-time updates and simple data structure. Which Firebase database should you choose and why?

hard

A. Firestore, because it supports complex queries and offline caching

B. Firestore, because it scales better for large datasets

C. Realtime Database, because it stores data in collections and documents

D. Realtime Database, because it syncs data instantly as a JSON tree

Solution

1. Step 1: Analyze app requirements

   The chat app needs fast real-time updates and a simple data structure.

2. Step 2: Match requirements to database features

   Realtime Database syncs data instantly as a JSON tree, ideal for simple real-time apps.

3. Step 3: Eliminate incorrect options

   Firestore supports complex queries and scales well but is more complex; Realtime Database does not use collections/documents.

4. Final Answer:

   Realtime Database, because it syncs data instantly as a JSON tree -> Option D

5. Quick Check:

   Simple real-time chat = Realtime Database [OK]

Hint: Fast real-time + simple data? Pick Realtime Database [OK]

Common Mistakes:

• Choosing Firestore for simple real-time needs
• Confusing data structure of Realtime Database
• Assuming Realtime Database uses collections/documents