Why Firestore CRUD operations in React Native? - Purpose & Use Cases

The Big Idea

What if your app could update data instantly without any hassle or mistakes?

The Scenario

Imagine you have a notebook where you write down all your friends' contact details. Every time you want to add a new friend, update a phone number, or remove someone, you have to flip through pages manually and rewrite everything carefully.

The Problem

This manual way is slow and easy to mess up. You might lose pages, write wrong numbers, or forget to update some details. It's hard to keep everything organized and up-to-date, especially when your list grows big.

The Solution

Firestore CRUD operations let your app handle data like a smart assistant. You can add, read, update, and delete information quickly and safely without flipping pages. It keeps everything organized and instantly available to your app users.

Before vs After

✗ Before

const friends = [];
friends.push({name: 'Anna', phone: '123'});
// To update, find and change manually

✓ After

await firestore.collection('friends').add({name: 'Anna', phone: '123'});
await firestore.collection('friends').doc(id).update({phone: '456'});

What It Enables

It makes your app dynamic and responsive, letting users see and change data instantly without confusion or delay.

Real Life Example

Think of a chat app where messages appear live, or a shopping list app where you can add or remove items anytime, and everyone sees the changes immediately.

Key Takeaways

Manual data handling is slow and error-prone.

Firestore CRUD operations automate data management safely.

This makes apps faster, more reliable, and user-friendly.

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