Firestore CRUD operations in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Firestore from Firebase in React Native.

React Native

import [1] from '@react-native-firebase/firestore';

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

Afirestore

Bdatabase

Cauth

Dstorage

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'database' instead of 'firestore'.

Confusing Firestore with Firebase Auth or Storage.

The Firestore module is imported as firestore from @react-native-firebase/firestore.

2fill in blank

medium

Complete the code to get a reference to a Firestore collection named 'users'.

React Native

const usersCollection = firestore().[1]('users');

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

Adoc

Bcollection

Cref

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'doc' which refers to a single document, not a collection.

Using 'get' which fetches data but does not return a reference.

Use collection('users') to get a reference to the 'users' collection in Firestore.

3fill in blank

hard

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

React Native

await firestore().collection('users').[1]({ name: 'Alice', age: 30 });

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

Aadd

Bget

Cupdate

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' without a document reference causes an error.

Using 'update' requires an existing document reference.

Use add() to create a new document with an auto-generated ID in a collection.

4fill in blank

hard

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

React Native

await firestore().collection('users').[1]('user123').[2]({ age: 31 });

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

Adoc

Badd

Cupdate

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' instead of 'doc' to get a document reference.

Using 'set' which replaces the whole document instead of updating.

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

5fill in blank

hard

Fill all three blanks to delete a document with ID 'user456' from the 'users' collection.

React Native

await firestore().[1]('users').[2]('[3]').delete();

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

Acollection

Buser456

Cdoc

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' instead of 'doc' to get document reference.

Passing the document ID to collection instead of doc.

To delete a document, get the collection, then the document by ID, then call delete().

Practice

1. What does the collection() function do in Firestore when used in React Native?

easy

A. It points to a group of documents in the database.

B. It creates a new document with data.

C. It deletes a document from the database.

D. It updates fields inside a document.

Solution

1. Step 1: Understand Firestore data structure

   Firestore organizes data in collections which contain documents.

2. Step 2: Role of collection()

   The collection() function points to a specific collection (group of documents) in Firestore.

3. Final Answer:

   It points to a group of documents in the database. -> Option A

4. Quick Check:

   collection() = points to documents group [OK]

Hint: Remember: collection() targets groups, doc() targets single items [OK]

Common Mistakes:

• Confusing collection() with doc()
• Thinking collection() creates data
• Mixing update and delete operations

2. Which of the following is the correct syntax to add a new document with data to a Firestore collection named 'users'?

easy

A. await addDoc(collection(db, 'users'), {name: 'Anna', age: 25});

B. await db.collection('users').add({name: 'Anna', age: 25});

C. await setDoc(doc(db, 'users'), {name: 'Anna', age: 25});

D. await updateDoc(collection(db, 'users'), {name: 'Anna', age: 25});

Solution

1. Step 1: Identify correct Firestore add syntax in React Native

   The addDoc function adds a new document to a collection.

2. Step 2: Check the syntax correctness

   await addDoc(collection(db, 'users'), {name: 'Anna', age: 25}); uses addDoc(collection(db, 'users'), data) which is the correct modern syntax.

3. Final Answer:

   await addDoc(collection(db, 'users'), {name: 'Anna', age: 25}); -> Option A

4. Quick Check:

   Add new doc = addDoc(collection(db, 'name'), data) [OK]

Hint: Use addDoc with collection() to add new documents [OK]

Common Mistakes:

• Using setDoc without doc() reference
• Calling updateDoc on a collection instead of a document
• Using deprecated syntax from older SDK versions

3. Given this code snippet, what will be logged to the console?

const docRef = doc(db, 'tasks', 'task1');
await updateDoc(docRef, {completed: true});
const docSnap = await getDoc(docRef);
console.log(docSnap.data());

medium

A. { completed: false }

B. { completed: true }

C. An error because updateDoc cannot be awaited

D. undefined

Solution

1. Step 1: Understand updateDoc effect

   The updateDoc call sets the field completed to true in the document 'task1'.

2. Step 2: Reading updated document data

   The getDoc fetches the updated document, so docSnap.data() returns the updated fields.

3. Final Answer:

   { completed: true } -> Option B

4. Quick Check:

   updateDoc changes data, getDoc reads updated data [OK]

Hint: updateDoc changes data; getDoc reads fresh data [OK]

Common Mistakes:

• Assuming updateDoc returns data
• Forgetting to await async calls
• Expecting old data without re-fetching

4. Identify the error in this Firestore delete operation code:

const docRef = doc(db, 'notes', 'note1');
await deleteDoc(collection(db, 'notes', 'note1'));

medium

A. The collection path is missing a document ID.

B. doc() cannot be used to get a document reference.

C. deleteDoc must be called without await.

D. deleteDoc should receive a document reference, not a collection.

Solution

1. Step 1: Check deleteDoc argument type

   The deleteDoc function requires a document reference, not a collection reference.

2. Step 2: Analyze the code's argument

   The code passes collection(db, 'notes', 'note1') which is invalid because collection() does not accept a document ID.

3. Final Answer:

   deleteDoc should receive a document reference, not a collection. -> Option D

4. Quick Check:

   deleteDoc(docRef) not deleteDoc(collection(...)) [OK]

Hint: deleteDoc needs doc(), not collection() [OK]

Common Mistakes:

• Passing collection() instead of doc() to deleteDoc
• Misunderstanding collection() parameters
• Omitting await on async calls

5. You want to update a user's profile in Firestore only if the 'age' field exists and is less than 30. Which code snippet correctly performs this conditional update?

hard

A. const docRef = doc(db, 'users', 'user1');
await updateDoc(docRef, {status: 'young'});
const docSnap = await getDoc(docRef);
if (docSnap.data().age >= 30) {
await deleteDoc(docRef);
}

B. await updateDoc(doc(db, 'users', 'user1'), {status: 'young', age: 30});

C. const docRef = doc(db, 'users', 'user1');
const docSnap = await getDoc(docRef);
if (docSnap.exists() && docSnap.data().age < 30) {
await updateDoc(docRef, {status: 'young'});
}

D. const docRef = doc(db, 'users', 'user1');
await setDoc(docRef, {status: 'young'}, {merge: true});

Solution

1. Step 1: Check for field existence and condition

   Use getDoc to read the document and verify if 'age' exists and is less than 30.

2. Step 2: Conditionally update document

   If condition is true, call updateDoc to update the 'status' field without overwriting other data.

3. Final Answer:

   Code snippet that reads, checks, then updates conditionally. -> Option C

4. Quick Check:

   Read first, then update if condition true [OK]

Hint: Always read document before conditional update [OK]

Common Mistakes:

• Updating without checking field existence
• Using setDoc without merge causing overwrite
• Deleting document incorrectly after update