Writing data (set, update, push) in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to write data to a Firebase Realtime Database using the set method.

Firebase

firebase.database().ref('users/user1').[1]({ name: 'Alice', age: 30 });

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

Aset

Bget

Cupdate

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using push instead of set will add a new child with a unique key.

Using update will only change specified fields without replacing all data.

The set method writes data to the specified database reference, replacing any existing data.

2fill in blank

medium

Complete the code to update only the age field of a user in Firebase Realtime Database.

Firebase

firebase.database().ref('users/user1').[1]({ age: 31 });

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

Aupdate

Bpush

Cset

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using set will overwrite all data at the reference.

Using push is for adding new child nodes, not updating existing data.

The update method modifies only the specified fields without overwriting the entire data at the reference.

3fill in blank

hard

Fix the error in the code to add a new message to the messages list using push.

Firebase

firebase.database().ref('messages').[1]({ text: 'Hello', timestamp: Date.now() });

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

Aupdate

Bpush

Cset

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using set will overwrite the entire messages list.

Using update requires a specific child key to update.

The push method adds a new child node with a unique key under the specified reference.

4fill in blank

hard

Fill both blanks to update the user's email and add a new phone number using push.

Firebase

const userRef = firebase.database().ref('users/user2');
userRef.[1]({ email: '[e-mail]' });
userRef.child('phones').[2]('123-456-7890');

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

Aupdate

Bset

Cpush

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using set for email will overwrite all user data.

Using update to add a phone number will not create a new child node.

Use update to change the email without overwriting other data, and push to add a new phone number as a child with a unique key.

5fill in blank

hard

Fill all three blanks to set a new post, update its title, and add a comment using push.

Firebase

const postRef = firebase.database().ref('posts/post1');
postRef.[1]({ title: 'First Post', content: 'Hello world!' });
postRef.[2]({ title: 'Updated Post Title' });
postRef.child('comments').[3]({ text: 'Nice post!' });

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

Aset

Bupdate

Cpush

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using update first without set will fail if the post does not exist.

Using set to update the title will overwrite the entire post.

Using update to add a comment will not create a new child node.

First, set creates the post. Then, update changes the title without removing content. Finally, push adds a new comment with a unique key.

Practice

1. Which Firebase method would you use to completely replace all data at a specific database path?

easy

A. push()

B. update()

C. set()

D. get()

Solution

1. Step 1: Understand set() behavior

   The set() method writes data to a specified path and replaces any existing data there.

2. Step 2: Compare with other methods

   update() modifies specific fields without replacing all data, push() adds new child nodes, and get() reads data.

3. Final Answer:

   set() -> Option C

4. Quick Check:

   Replace all data = set() [OK]

Hint: Use set() to overwrite all data at a path [OK]

Common Mistakes:

• Confusing update() with set() and expecting full replacement
• Using push() when needing to replace data
• Thinking get() writes data

2. Which of the following is the correct syntax to add a new child with a unique key under the path 'messages' using Firebase Realtime Database?

easy

A. firebase.database().ref('messages').set({ text: 'Hello' })

B. firebase.database().ref('messages').push({ text: 'Hello' })

C. firebase.database().ref('messages').update({ text: 'Hello' })

D. firebase.database().ref('messages').get({ text: 'Hello' })

Solution

1. Step 1: Identify method for unique child addition

   The push() method adds a new child with a unique key under the specified path.

2. Step 2: Check syntax correctness

   Using push({ text: 'Hello' }) under 'messages' correctly adds a new message with unique key.

3. Final Answer:

   firebase.database().ref('messages').push({ text: 'Hello' }) -> Option B

4. Quick Check:

   Unique child addition = push() [OK]

Hint: Use push() to add unique child nodes [OK]

Common Mistakes:

• Using set() which overwrites all children
• Using update() which only modifies existing fields
• Using get() which only reads data

3. Given the following Firebase code snippet:

firebase.database().ref('users/user1').update({ age: 30 });

What will happen to the existing data at 'users/user1' if it currently contains { name: 'Alice', age: 25 }?

medium

A. Only the 'age' field is updated to 30; 'name' remains 'Alice'

B. The entire 'users/user1' data is replaced with { age: 30 }

C. A new child with key 'age' is added under 'user1'

D. An error occurs because update() cannot be used here

Solution

1. Step 1: Understand update() behavior

   The update() method modifies only the specified fields without removing other existing data.

2. Step 2: Apply to given data

   Since 'age' is updated to 30, 'name' remains unchanged as 'Alice'.

3. Final Answer:

   Only the 'age' field is updated to 30; 'name' remains 'Alice' -> Option A

4. Quick Check:

   update() changes fields, keeps others [OK]

Hint: update() changes fields, keeps others intact [OK]

Common Mistakes:

• Thinking update() replaces all data like set()
• Confusing push() with update()
• Expecting an error when update() is valid

4. You want to update the user's email without removing other user data. Which Firebase method usage below contains an error?

medium

A. firebase.database().ref('users/user1').update({ email: '[e-mail]' })

B. firebase.database().ref('users/user1/email').set('[e-mail]')

C. firebase.database().ref('users/user1').update({ email: '[e-mail]', phone: '1234567890' })

D. firebase.database().ref('users/user1').push({ email: '[e-mail]' })

Solution

1. Step 1: Understand push() usage

   push() adds a new child with a unique key; it does not update existing fields.

2. Step 2: Analyze the goal

   To update email without removing other data, update() is correct; push() wrongly adds a new child instead.

3. Final Answer:

   Using push() to update email is incorrect -> Option D

4. Quick Check:

   push() adds new child, not update fields [OK]

Hint: Use update() to change fields, not push() [OK]

Common Mistakes:

• Using push() to update existing fields
• Using set() which overwrites all data
• Confusing update() and push() roles

5. You want to add multiple chat messages under 'chats' in Firebase Realtime Database, each with a unique key, and also update the user's last active timestamp without overwriting existing data. Which combination of methods should you use?

hard

A. Use push() for messages and update() for last active timestamp

B. Use push() for messages and set() for last active timestamp

C. Use update() for messages and set() for last active timestamp

D. Use set() for messages and update() for last active timestamp

Solution

1. Step 1: Add multiple messages with unique keys

   Use push() under 'chats' to add each message with a unique key without overwriting others.

2. Step 2: Update last active timestamp without overwriting

   Use update() on the user's data to change the timestamp without removing other fields.

3. Final Answer:

   Use push() for messages and update() for last active timestamp -> Option A

4. Quick Check:

   push() adds unique children, update() modifies fields [OK]

Hint: push() for new items, update() for field changes [OK]

Common Mistakes:

• Using set() for messages which overwrites all chats
• Using set() for timestamp which removes other user data
• Using update() to add unique children