Updating specific fields in Firebase - Step-by-Step Execution

Process Flow - Updating specific fields

Start

↓

Select Document

↓

Specify Fields to Update

↓

Send Update Request

↓

Database Applies Changes

↓

Confirm Update Success

↓

End

This flow shows how to update only certain fields in a Firebase document without changing the whole document.

Execution Sample

Firebase

docRef.update({
  age: 30,
  city: 'New York'
});

Updates only the 'age' and 'city' fields of the selected document.

Process Table

Step	Action	Fields Sent	Database State Before	Database State After	Result
1	Select document 'user123'	N/A	{name: 'Alice', age: 25, city: 'Boston'}	{name: 'Alice', age: 25, city: 'Boston'}	Document selected
2	Call update() with {age: 30, city: 'New York'}	{age: 30, city: 'New York'}	{name: 'Alice', age: 25, city: 'Boston'}	{name: 'Alice', age: 30, city: 'New York'}	Fields updated
3	Confirm update success	N/A	{name: 'Alice', age: 30, city: 'New York'}	{name: 'Alice', age: 30, city: 'New York'}	Update confirmed

💡 Update completes after specified fields are changed; other fields remain unchanged.

Status Tracker

Variable	Start	After Step 2	Final
docRef	Reference to 'user123'	Reference to 'user123'	Reference to 'user123'
age	25	30	30
city	'Boston'	'New York'	'New York'
name	'Alice'	'Alice'	'Alice'

Key Moments - 2 Insights

Why does the 'name' field stay the same after update?

Because update() changes only the specified fields (age and city). Fields not listed, like 'name', stay unchanged as shown in execution_table row 2.

What happens if you try to update a field that does not exist yet?

Firebase creates the new field with the given value. This is like adding a new key to the document, similar to how age and city were updated in the example.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'city' after step 2?

A 'Boston'

B 'New York'

C undefined

D 'Chicago'

💡 Hint

Check the 'Database State After' column in row 2 of the execution_table.

At which step does the database state actually change?

A Step 2

B Step 1

C Step 3

D No change occurs

💡 Hint

Look at the 'Database State After' column and see when fields are updated.

If you add a new field 'email' in the update call, what happens to the document?

A The document is replaced entirely with only 'email'

B The update fails because 'email' does not exist

C Only 'email' is added or updated, other fields stay the same

D All fields are deleted except 'email'

💡 Hint

Refer to the key_moments explanation about adding new fields.

Concept Snapshot

Firebase update() changes only specified fields in a document.
Unspecified fields remain unchanged.
New fields can be added by including them in update().
update() does not replace the whole document.
Use update() to modify parts without overwriting all data.

Full Transcript

This visual execution shows how Firebase updates specific fields in a document. First, a document is selected. Then, update() is called with only the fields to change. The database changes those fields but keeps others intact. The update is confirmed successful. This method avoids overwriting the entire document and allows adding new fields easily.