Why Firestore is Firebase's primary database - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firestore in a Firebase app.

Firebase

const db = firebase.[1]();

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

Astorage

Bauth

Cfirestore

Ddatabase

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'database()' initializes the Realtime Database, not Firestore.

The firestore() method initializes Firestore, Firebase's primary database.

2fill in blank

medium

Complete the code to add a document to a Firestore collection.

Firebase

db.collection('users').[1]({ name: 'Alice', age: 30 });

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

Aadd

Bset

Cupdate

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' on a collection causes an error.

The add() method adds a new document with an auto-generated ID to the collection.

3fill in blank

hard

Fix the error in the code to get a document by ID from Firestore.

Firebase

db.collection('users').doc([1]).get().then(doc => { if (doc.exists) { console.log(doc.data()); } });

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

AdocId

BuserId

Cuser.id

D'userId'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing variable names without quotes when they are not defined.

The document ID must be a string. Using quotes around 'userId' passes the ID correctly.

4fill in blank

hard

Fill both blanks to query Firestore for users older than 25 and order by age.

Firebase

db.collection('users').where('age', [1], 25).[2]('age').get();

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A>

BorderBy

C<

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for filtering older users.

The where clause filters users older than 25 using '>'. The orderBy method sorts results by age.

5fill in blank

hard

Fill all three blanks to update a user's email and log success.

Firebase

db.collection('users').doc([1]).[2]({ email: [3] }).then(() => { console.log('Email updated'); });

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

A'user123'

Bupdate

C'[e-mail]'

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using set overwrites the whole document.

The doc method needs the document ID as a string. The update method changes fields without overwriting the whole document. The new email must be a string.

Practice

1. Why is Firestore considered Firebase's primary database?

easy

A. Because it only stores data temporarily

B. Because it requires manual scaling for large apps

C. Because it updates data in real time and works offline

D. Because it does not support security rules

Solution

1. Step 1: Understand Firestore's real-time update feature

   Firestore automatically updates data in real time, so apps stay current without manual refresh.

2. Step 2: Recognize offline support and automatic scaling

   Firestore works offline and scales automatically, making it easy to use and reliable.

3. Final Answer:

   Because it updates data in real time and works offline -> Option C

4. Quick Check:

   Real-time + offline = Firestore primary [OK]

Hint: Remember Firestore updates live and works offline [OK]

Common Mistakes:

• Thinking Firestore needs manual scaling
• Believing Firestore lacks security rules
• Confusing Firestore with temporary storage

2. Which of the following is the correct way to define a Firestore collection reference in Firebase SDK?

easy

A. const ref = firestore.collection('users');

B. const ref = firestore.getCollection('users');

C. const ref = firestore.users.collection();

D. const ref = firestore.collection.users();

Solution

1. Step 1: Recall Firestore collection syntax

   The correct method to get a collection reference is firestore.collection('collectionName').

2. Step 2: Check each option's syntax

   Only const ref = firestore.collection('users'); uses the correct method name and syntax.

3. Final Answer:

   const ref = firestore.collection('users'); -> Option A

4. Quick Check:

   Use .collection('name') to get collection [OK]

Hint: Use .collection('name') to get Firestore collections [OK]

Common Mistakes:

• Using getCollection instead of collection
• Accessing collection as a property
• Calling collection as a method on collection

3. Given this Firestore query code, what will be the output if the 'users' collection has documents with fields {name: 'Alice', age: 30} and {name: 'Bob', age: 25}?

const snapshot = await firestore.collection('users').where('age', '>', 26).get();
const names = snapshot.docs.map(doc => doc.data().name);
console.log(names);

medium

A. ['Alice']

B. ['Bob']

C. ['Alice', 'Bob']

D. []

Solution

1. Step 1: Analyze the query condition

   The query filters users where age is greater than 26.

2. Step 2: Check which users match the condition

   Alice is 30 (matches), Bob is 25 (does not match).

3. Final Answer:

   ['Alice'] -> Option A

4. Quick Check:

   Age > 26 returns Alice only [OK]

Hint: Filter by age > 26 returns only Alice [OK]

Common Mistakes:

• Including Bob who is 25
• Returning empty array by mistake
• Returning both users ignoring filter

4. Which of the following correctly describes this Firestore security rule snippet?

service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow read, write: if request.auth.uid == userId;
    }
  }
}

medium

A. It does not allow any access to users

B. It allows read and write only if user is authenticated and matches userId

C. It allows access without authentication

D. It has syntax errors in the match statements

Solution

1. Step 1: Understand the rule condition

   The rule allows read and write only if the authenticated user's ID matches the document's userId.

2. Step 2: Check for errors or incorrect logic

   The syntax is correct and the logic restricts access properly.

3. Final Answer:

   It allows read and write only if user is authenticated and matches userId -> Option B

4. Quick Check:

   Auth check with userId match = correct rule [OK]

Hint: Check if auth uid matches userId for access [OK]

Common Mistakes:

• Thinking it allows access without auth
• Assuming syntax errors exist
• Believing it denies all access

5. You want to build a chat app that works offline and syncs messages automatically when online. Why is Firestore the best choice for this?

hard

A. Because Firestore only stores data temporarily in memory

B. Because Firestore requires manual syncing and no offline support

C. Because Firestore does not support real-time updates

D. Because Firestore supports offline data persistence and real-time syncing

Solution

1. Step 1: Identify offline support in Firestore

   Firestore caches data locally, so apps work offline without errors.

2. Step 2: Recognize real-time syncing feature

   When online, Firestore syncs changes automatically to keep data updated.

3. Step 3: Compare with other options

   Options A, B, and D contradict Firestore's key features.

4. Final Answer:

   Because Firestore supports offline data persistence and real-time syncing -> Option D

5. Quick Check:

   Offline + real-time sync = Firestore best for chat [OK]

Hint: Offline persistence + real-time sync = Firestore wins [OK]

Common Mistakes:

• Thinking Firestore needs manual sync
• Believing Firestore lacks offline support
• Confusing Firestore with temporary storage