Writing data (set, update, push) in Firebase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the set() method do in Firebase Realtime Database?

The set() method writes data to a specified location, replacing any existing data at that path with the new data.

beginner

How does update() differ from set() in Firebase?

update() modifies specific child keys without overwriting the entire data at the location, while set() replaces all data at the location.

beginner

What is the purpose of the push() method in Firebase Realtime Database?

push() creates a new child node with a unique key under a specified path, useful for adding items to lists without overwriting existing data.

intermediate

When should you use update() instead of set()?

Use update() when you want to change only some fields of a data object without removing other existing fields.

beginner

What happens if you use set() on a path that already has data?

The existing data at that path is completely replaced by the new data you provide in set().

Which Firebase method adds a new item with a unique key to a list?

A push()

B set()

C update()

D get()

push() creates a new child node with a unique key, perfect for adding list items.

What does set() do if the target path already contains data?

A Merges new data with existing data

B Updates only specified fields

C Deletes the data

D Replaces existing data completely

set() replaces all data at the path with the new data.

Which method should you use to change only some fields without removing others?

A set()

B update()

C push()

D remove()

update() modifies specific fields without deleting other data.

If you want to add a new message to a chat list, which method is best?

A set()

B update()

C push()

D get()

push() adds a new unique child ideal for chat messages.

Which method can overwrite the entire data at a database path?

A set()

B push()

C transaction()

D update()

set() replaces all data at the specified path.

Explain the differences between set(), update(), and push() in Firebase Realtime Database.

Think about how each method affects existing data.

Describe a real-life scenario where you would use push() instead of set() or update().

Consider situations where multiple users add data simultaneously.

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