Deleting documents in Firebase - Mini Project: Build & Apply

Deleting documents in Firebase Firestore

📖 Scenario: You are managing a simple app that stores user profiles in Firebase Firestore. Sometimes, you need to remove a user profile when it is no longer needed.

🎯 Goal: Learn how to delete a specific document from a Firestore collection using Firebase SDK.

📋 What You'll Learn

Create a Firestore collection reference

Specify the document ID to delete

Use the Firebase SDK method to delete the document

Confirm the deletion code is correctly structured

💡 Why This Matters

🌍 Real World

Deleting documents is common when users remove their accounts or when data needs cleanup in apps using Firestore.

💼 Career

Understanding how to delete documents safely and correctly is essential for backend and full-stack developers working with Firebase.

1

Set up Firestore collection reference

Create a constant called usersCollection that references the Firestore collection named users using collection(db, 'users').

Firebase

// Your code here

Hint

Use the collection function from Firebase Firestore and pass db and the collection name 'users'.

2

Specify the document ID to delete

Create a constant called userIdToDelete and set it to the string 'user123', which is the ID of the user document to delete.

Firebase

import { collection } from 'firebase/firestore';

const usersCollection = collection(db, 'users');

// Your code here

Hint

Assign the exact string 'user123' to the constant userIdToDelete.

3

Create a document reference for deletion

Create a constant called userDocRef that references the document to delete by using doc(usersCollection, userIdToDelete).

Firebase

import { collection, doc } from 'firebase/firestore';

const usersCollection = collection(db, 'users');

const userIdToDelete = 'user123';

// Your code here

Hint

Use the doc function with usersCollection and userIdToDelete to get the document reference.

4

Delete the document using Firebase SDK

Write an async function called deleteUserDocument that calls deleteDoc(userDocRef) to delete the document. Use await inside the function.

Firebase

import { collection, doc } from 'firebase/firestore';
import { deleteDoc } from 'firebase/firestore';

const usersCollection = collection(db, 'users');

const userIdToDelete = 'user123';

const userDocRef = doc(usersCollection, userIdToDelete);

// Your code here

Hint

Define an async function and use await deleteDoc(userDocRef) inside it to delete the document.

Practice

1. What does the delete() method do in Firebase Firestore?

easy

A. Reads data from a document

B. Adds a new document to the database

C. Updates fields in an existing document

D. Removes a specific document from the database

Solution

1. Step 1: Understand the purpose of delete()

   The delete() method is used to remove a document from Firestore.

2. Step 2: Compare with other operations

   Adding, updating, and reading documents use different methods like set(), update(), and get().

3. Final Answer:

   Removes a specific document from the database -> Option D

4. Quick Check:

   delete() removes documents [OK]

Hint: Delete removes documents, not adds or updates [OK]

Common Mistakes:

• Confusing delete() with set() or update()
• Thinking delete() reads data
• Assuming delete() removes collections

2. Which of the following is the correct syntax to delete a document with ID 'doc1' from a collection 'users' in Firestore?

easy

A. db.collection('users').doc('doc1').remove()

B. db.collection('users').delete('doc1')

C. db.collection('users').doc('doc1').delete()

D. db.delete('users/doc1')

Solution

1. Step 1: Identify correct method to delete a document

   The method to delete a document is delete() called on a document reference.

2. Step 2: Check syntax for document reference

   Use collection('users').doc('doc1') to get the document, then call delete().

3. Final Answer:

   db.collection('users').doc('doc1').delete() -> Option C

4. Quick Check:

   Use doc().delete() to remove documents [OK]

Hint: Use doc('id').delete() to remove a document [OK]

Common Mistakes:

• Using remove() instead of delete()
• Calling delete() on collection instead of doc
• Wrong method chaining order

3. What will the following code output if the document 'doc1' exists and is deleted successfully?

db.collection('users').doc('doc1').delete()
  .then(() => console.log('Deleted'))
  .catch(() => console.log('Error'))

medium

A. Error

B. Deleted

C. Nothing

D. SyntaxError

Solution

1. Step 1: Understand promise handling in delete()

   The delete() method returns a promise that resolves on success and rejects on failure.

2. Step 2: Analyze the then/catch handlers

   If deletion succeeds, then() runs and logs 'Deleted'. If it fails, catch() logs 'Error'.

3. Final Answer:

   Deleted -> Option B

4. Quick Check:

   Successful delete logs 'Deleted' [OK]

Hint: Successful delete triggers then(), logs 'Deleted' [OK]

Common Mistakes:

• Assuming delete() is synchronous
• Ignoring promise handling
• Expecting output without then()

4. Identify the error in this code snippet that tries to delete a document:

const docRef = db.collection('users').doc('doc1');
docRef.delete;
console.log('Deleted');

medium

A. Missing parentheses after delete method call

B. Wrong collection name

C. docRef is not defined

D. delete is not a method

Solution

1. Step 1: Check method invocation syntax

   The delete method must be called with parentheses: delete().

2. Step 2: Identify impact of missing parentheses

   Without parentheses, the method is not executed, so the document is not deleted.

3. Final Answer:

   Missing parentheses after delete method call -> Option A

4. Quick Check:

   Call delete() with () to execute [OK]

Hint: Always use parentheses to call delete() method [OK]

Common Mistakes:

• Forgetting () after delete
• Assuming delete is a property, not a method
• Ignoring promise handling

5. You want to delete multiple documents with IDs ['doc1', 'doc2', 'doc3'] from the 'users' collection. Which approach correctly deletes all documents and logs 'All deleted' after completion?

hard

A. Use Promise.all with delete promises:Promise.all(['doc1','doc2','doc3'].map(id => db.collection('users').doc(id).delete()))
.then(() => console.log('All deleted'))

B. Call delete() on the collection:db.collection('users').delete();
console.log('All deleted');

C. Use a loop with await:for (const id of ['doc1','doc2','doc3']) {
await db.collection('users').doc(id).delete();
}
console.log('All deleted');

D. Delete documents without waiting:['doc1','doc2','doc3'].forEach(id => db.collection('users').doc(id).delete());
console.log('All deleted');

Solution

1. Step 1: Understand asynchronous deletion of multiple documents

   Deleting multiple documents returns promises; to know when all finish, use Promise.all().

2. Step 2: Evaluate each option's correctness

   Use Promise.all with delete promises:
   

   Promise.all(['doc1','doc2','doc3'].map(id => db.collection('users').doc(id).delete()))
     .then(() => console.log('All deleted'))

   uses Promise.all() with delete promises to wait for all deletions concurrently before logging. B calls invalid delete() on collection. C uses await loop without async function, causing syntax error. D logs without waiting for completion.

3. Final Answer:

   Use Promise.all with delete promises -> Option A

4. Quick Check:

   Promise.all waits for all deletes before logging [OK]

Hint: Use Promise.all to wait for all deletes before logging [OK]

Common Mistakes:

• Trying to delete entire collection directly
• Not waiting for all deletes before logging
• Using forEach without async/await or Promise.all