Cloud Firestore CRUD in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Firestore package in Flutter.

Flutter

import 'package:cloud_firestore/[1].dart';

Drag options to blanks, or click blank then click option'

Afirestore

Bfirebase

Cfirestore_core

Dfirestore_flutter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'firebase' instead of 'firestore' in the import path.

Trying to import 'firestore_flutter' which does not exist.

The correct import for Firestore in Flutter is cloud_firestore/firestore.dart.

2fill in blank

medium

Complete the code to get a Firestore instance in Flutter.

Flutter

final FirebaseFirestore firestore = FirebaseFirestore.[1];

Drag options to blanks, or click blank then click option'

Ainitialize

Binstance

CgetInstance

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'getInstance()' which is not defined in Flutter Firestore.

Trying to call 'initialize()' or 'create()' which do not exist.

Use FirebaseFirestore.instance to get the Firestore instance.

3fill in blank

hard

Fix the error in the code to add a new document to the 'users' collection.

Flutter

await firestore.collection('users').[1]({'name': 'Alice', 'age': 25});

Drag options to blanks, or click blank then click option'

Aupdate

Binsert

Cset

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' which requires an existing document.

Using 'set' without specifying a document ID.

Using 'insert' which is not a Firestore method.

To add a new document with an auto-generated ID, use add().

4fill in blank

hard

Fill both blanks to update the 'age' field of a user document with ID 'user123'.

Flutter

await firestore.collection('users').doc([1]).[2]({'age': 30});

Drag options to blanks, or click blank then click option'

A'user123'

Bupdate

Cset

D'user456'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' which overwrites the whole document.

Using wrong document ID like 'user456'.

Use doc('user123') to select the document, then update() to change fields.

5fill in blank

hard

Fill all three blanks to delete a document with ID 'doc789' from the 'items' collection.

Flutter

await firestore.collection([1]).doc([2]).[3]();

Drag options to blanks, or click blank then click option'

A'items'

B'doc789'

Cdelete

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'remove' which is not a Firestore method.

Using wrong collection or document IDs.

Use collection('items'), then doc('doc789'), and finally delete() to remove the document.

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