Writing data (set, update, push) in Firebase - Step-by-Step Execution

Process Flow - Writing data (set, update, push)

Start

↓

Choose write method

↓

set()

↓

Overwrite data

↓

Confirm write success

↓

End

This flow shows choosing between set, update, and push to write data in Firebase, then performing the write and confirming success.

Execution Sample

Firebase

ref.set({name: 'Alice'});
ref.update({age: 30});
ref.push({score: 100});

This code writes data by overwriting, updating fields, and adding a new child in Firebase.

Process Table

Step	Action	Data Sent	Effect on Database	Result
1	Call set()	{name: 'Alice'}	Overwrite data at ref with {name: 'Alice'}	Data at ref is now {name: 'Alice'}
2	Call update()	{age: 30}	Add/modify 'age' field, keep other fields	Data at ref is now {name: 'Alice', age: 30}
3	Call push()	{score: 100}	Add new child with unique key under ref	New child created with {score: 100}
4	Confirm writes	N/A	All writes succeeded	Database updated successfully

💡 All write operations completed successfully with expected data changes.

Status Tracker

Variable	Start	After set()	After update()	After push()
Database at ref	{}	{name: 'Alice'}	{name: 'Alice', age: 30}	{name: 'Alice', age: 30, newChildKey: {score: 100}}

Key Moments - 3 Insights

Why does set() overwrite all data at the reference?

Because set() replaces the entire data at the reference, as shown in step 1 of the execution_table where previous data is replaced by {name: 'Alice'}.

How does update() differ from set() in modifying data?

update() only changes specified fields without removing others, as seen in step 2 where 'age' is added but 'name' remains.

What does push() do differently compared to set() and update()?

push() creates a new child with a unique key under the reference, adding data without overwriting existing data, shown in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the database content after step 2?

A {name: 'Alice', age: 30}

B {age: 30}

C {name: 'Alice'}

D {}

💡 Hint

Check the 'Effect on Database' and 'Result' columns for step 2 in the execution_table.

At which step does the database get a new child with a unique key?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for the action 'Call push()' in the execution_table.

If you want to replace all data at a reference, which method should you use?

A update()

B set()

C push()

D None of these

💡 Hint

Refer to the explanation of set() in the key_moments and execution_table step 1.

Concept Snapshot

Firebase Writing Data:
- set(): Overwrites all data at a reference.
- update(): Modifies specified fields, keeps others.
- push(): Adds new child with unique key.
Use set() to replace, update() to change fields, push() to add entries.

Full Transcript

This lesson shows how to write data in Firebase using set, update, and push methods. First, set() replaces all data at a location. Then, update() changes or adds specific fields without removing others. Finally, push() adds a new child with a unique key under the reference. Each step changes the database state as shown. Understanding these differences helps manage data safely and effectively in Firebase.

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