Cloud Firestore CRUD in Flutter

Introduction

Cloud Firestore lets your app save, read, update, and delete data in the cloud. This helps your app share data with users instantly and keep it safe.

You want to save user notes or messages online.

You need to show live updates to all users, like chat messages.

You want to keep user settings synced across devices.

You want to store app data without managing your own server.

You want to update or remove data easily from your app.

Syntax

Flutter

final docRef = FirebaseFirestore.instance.collection('collectionName').doc('docId');

// Create or update
await docRef.set({'field': 'value'});

// Read
final snapshot = await docRef.get();
final data = snapshot.data();

// Update
await docRef.update({'field': 'newValue'});

// Delete
await docRef.delete();

set() creates or replaces a document.

update() changes only specified fields.

Examples

This creates or replaces the 'user1' document with name and age.

Flutter

await FirebaseFirestore.instance.collection('users').doc('user1').set({'name': 'Alice', 'age': 25});

This reads the 'user1' document and prints its data.

Flutter

final snapshot = await FirebaseFirestore.instance.collection('users').doc('user1').get();
print(snapshot.data());

This updates only the age field of 'user1' document.

Flutter

await FirebaseFirestore.instance.collection('users').doc('user1').update({'age': 26});

This deletes the 'user1' document from the collection.

Flutter

await FirebaseFirestore.instance.collection('users').doc('user1').delete();

Sample App

This Flutter app shows buttons to add, update, get, and delete a user document in Firestore. The text updates to show the current action or data.

Flutter

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: FirestoreDemo(),
    );
  }
}

class FirestoreDemo extends StatefulWidget {
  @override
  _FirestoreDemoState createState() => _FirestoreDemoState();
}

class _FirestoreDemoState extends State<FirestoreDemo> {
  final CollectionReference users = FirebaseFirestore.instance.collection('users');

  Future<void> addUser() async {
    await users.doc('user1').set({'name': 'Alice', 'age': 25});
  }

  Future<void> updateUser() async {
    await users.doc('user1').update({'age': 26});
  }

  Future<void> deleteUser() async {
    await users.doc('user1').delete();
  }

  Future<Map<String, dynamic>?> getUser() async {
    final doc = await users.doc('user1').get();
    return doc.exists ? doc.data() as Map<String, dynamic>? : null;
  }

  String displayText = 'No data';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Firestore CRUD Demo')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(displayText),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: () async {
                await addUser();
                setState(() {
                  displayText = 'User added';
                });
              },
              child: Text('Add User'),
            ),
            ElevatedButton(
              onPressed: () async {
                await updateUser();
                setState(() {
                  displayText = 'User updated';
                });
              },
              child: Text('Update User'),
            ),
            ElevatedButton(
              onPressed: () async {
                final data = await getUser();
                setState(() {
                  displayText = data != null ? 'Name: ${data['name']}, Age: ${data['age']}' : 'User not found';
                });
              },
              child: Text('Get User'),
            ),
            ElevatedButton(
              onPressed: () async {
                await deleteUser();
                setState(() {
                  displayText = 'User deleted';
                });
              },
              child: Text('Delete User'),
            ),
          ],
        ),
      ),
    );
  }
}

Important Notes

Make sure to initialize Firebase in your app before using Firestore.

Use set() to create or replace documents, and update() to change only some fields.

Always check if a document exists before reading its data to avoid errors.

Summary

Cloud Firestore stores app data in collections and documents.

CRUD means Create, Read, Update, and Delete data.

Flutter uses FirebaseFirestore.instance to access Firestore and perform these actions.

Practice

1.

What does CRUD stand for in Cloud Firestore operations?

easy

A. Connect, Refresh, Upload, Delete

B. Copy, Run, Undo, Download

C. Create, Read, Update, Delete

D. Create, Remove, Update, Download

Solution

1. Step 1: Understand CRUD acronym meaning

   CRUD is a common term in databases meaning the four basic operations on data.

2. Step 2: Match each letter to the correct operation

   C = Create, R = Read, U = Update, D = Delete are the standard meanings.

3. Final Answer:

   Create, Read, Update, Delete -> Option C

4. Quick Check:

   CRUD = Create, Read, Update, Delete [OK]

Hint: Remember CRUD as basic data actions: create, read, update, delete [OK]

Common Mistakes:

• Confusing CRUD letters with unrelated words
• Mixing up 'Remove' with 'Delete'
• Thinking CRUD includes 'Download'

2.

Which Flutter code snippet correctly adds a new document to a Firestore collection named users?

FirebaseFirestore.instance.collection('users').____({'name': 'Alice'});

easy

A. update

B. add

C. delete

D. get

Solution

1. Step 1: Identify method to add new document

   The add method creates a new document with given data in the collection.

2. Step 2: Confirm other methods' purposes

   update modifies existing documents, delete removes documents, get reads data.

3. Final Answer:

   add -> Option B

4. Quick Check:

   Adding new document uses add() [OK]

Hint: Use add() to create new documents in a collection [OK]

Common Mistakes:

• Using update() to add new documents
• Confusing get() with add()
• Trying to delete() when adding data

3.

What will be the output of this Flutter Firestore code snippet?

var doc = await FirebaseFirestore.instance.collection('tasks').doc('task1').get();
print(doc.exists);

Assuming the document task1 exists in the tasks collection.

medium

A. true

B. false

C. null

D. Throws an error

Solution

1. Step 1: Understand doc.get() behavior

   The get() method fetches the document snapshot from Firestore.

2. Step 2: Check the exists property

   If the document exists, doc.exists returns true; otherwise false.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Document exists property = true [OK]

Hint: doc.exists is true if document is found in Firestore [OK]

Common Mistakes:

• Assuming doc.exists returns document data
• Expecting false even if document exists
• Not awaiting the get() call

4.

Identify the error in this Flutter Firestore update code:

FirebaseFirestore.instance.collection('users').doc('user1').update({'age': 30});

Assuming the document user1 does not exist.

medium

A. No error, update creates document if missing

B. Update silently fails without error

C. Syntax error in update method call

D. Throws an error because document does not exist

Solution

1. Step 1: Understand update() behavior on missing document

   The update() method requires the document to exist; otherwise, it throws an error.

2. Step 2: Confirm no syntax errors

   The syntax is correct, so error is due to missing document.

3. Final Answer:

   Throws an error because document does not exist -> Option D

4. Quick Check:

   update() fails if document missing [OK]

Hint: update() needs existing document; else error occurs [OK]

Common Mistakes:

• Thinking update() creates new documents
• Confusing update() with set()
• Ignoring async/await for update()

5.

You want to delete a Firestore document only if it exists to avoid errors. Which Flutter code snippet correctly does this?

var docRef = FirebaseFirestore.instance.collection('orders').doc('order1');
// What code to safely delete?

hard

A. docRef.get().then((doc) { if (doc.exists) docRef.delete(); });

B. docRef.delete();

C. docRef.update({'deleted': true});

D. docRef.set(null);

Solution

1. Step 1: Check document existence before deleting

   Use get() to fetch the document snapshot and check exists.

2. Step 2: Call delete() only if document exists

   This avoids errors from deleting non-existing documents.

3. Final Answer:

   docRef.get().then((doc) { if (doc.exists) docRef.delete(); }); -> Option A

4. Quick Check:

   Check exists before delete to avoid errors [OK]

Hint: Always check doc.exists before delete() to prevent errors [OK]

Common Mistakes:

• Calling delete() without checking existence
• Using update() to delete documents
• Setting document to null instead of deleting