Writing data (set, update, push) in Firebase - Mini Project: Build & Apply

Writing Data in Firebase Realtime Database

📖 Scenario: You are building a simple app to manage a list of tasks. You want to store tasks in Firebase Realtime Database. Each task has a title and a status.

🎯 Goal: Learn how to write data to Firebase Realtime Database using set, update, and push methods.

📋 What You'll Learn

Create an initial task object with exact fields

Create a reference path string for the tasks node

Use set to write a task to a specific path

Use update to change the status of a task

Use push to add a new task with a unique key

💡 Why This Matters

🌍 Real World

Writing and updating data in Firebase Realtime Database is common for apps like to-do lists, chat apps, and real-time dashboards.

💼 Career

Understanding how to write data using set, update, and push is essential for junior cloud developers and mobile app developers working with Firebase.

1

Create initial task data

Create a constant called task with an object containing title set to 'Buy groceries' and status set to 'pending'.

Firebase

# Create a constant called task with title 'Buy groceries' and status 'pending'
# Your code here

Hint

Use const task = { title: 'Buy groceries', status: 'pending' };

2

Create database reference path

Create a constant called tasksRef and set it to the string 'tasks' representing the database path for tasks.

Firebase

const task = { title: 'Buy groceries', status: 'pending' };
# Create a constant tasksRef with value 'tasks'
# Your code here

Hint

Use const tasksRef = 'tasks';

3

Write task data using set

Write the task object to the database path tasksRef + '/task1' using the set method from Firebase. Use set(ref(database, path), data) syntax.

Firebase

const task = { title: 'Buy groceries', status: 'pending' };
const tasksRef = 'tasks';
# Use set to write task to 'tasks/task1'
# Your code here

Hint

Use set(ref(database, tasksRef + '/task1'), task); to write data.

4

Update and push tasks

Use update to change the status of task1 to 'completed' at path tasksRef + '/task1'. Then use push to add a new task with title 'Walk the dog' and status 'pending' under tasksRef.

Firebase

import { getDatabase, ref, set, update, push } from 'firebase/database';

const database = getDatabase();
const task = { title: 'Buy groceries', status: 'pending' };
const tasksRef = 'tasks';

set(ref(database, tasksRef + '/task1'), task);
# Use update to set status of task1 to 'completed'
# Use push to add new task with title 'Walk the dog' and status 'pending'
# Your code here

Hint

Use update(ref(database, tasksRef + '/task1'), { status: 'completed' }) and push(ref(database, tasksRef), newTask).

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