Deleting documents in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete a document from Firestore.

Firebase

await firestore.collection('users').doc([1]).delete();

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

AdocId

BuserId

C'userId123'

Ddocument

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without quotes.

Forgetting to call the delete() method.

To delete a document, you need to specify its exact ID as a string inside doc().

2fill in blank

medium

Complete the code to delete a document using async/await syntax.

Firebase

async function removeDoc() {
  try {
    await firestore.collection('posts').doc([1]).delete();
  } catch (error) {
    console.error(error);
  }
}

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

ApostId

B'post123'

CdocRef

DdocumentId

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a variable without quotes.

Not awaiting the delete() call.

The document ID must be a string literal inside doc() to delete the correct document.

3fill in blank

hard

Fix the error in the code to delete a Firestore document.

Firebase

firestore.collection('orders').[1]('orderId123').delete();

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

Adoc

Bdelete

Cget

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using get() instead of doc().

Calling delete() without a document reference.

The doc() method is used to specify the document reference before calling delete().

4fill in blank

hard

Fill both blanks to delete a document and handle errors properly.

Firebase

firestore.collection('products').[1]([2]).delete().catch(error => console.error(error));

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

Adoc

B'prod456'

Cget

D'productId'

Attempts:

3 left

💡 Hint

Common Mistakes

Using get() instead of doc().

Passing a variable without quotes as document ID.

Use doc() with the exact document ID string to delete the document and catch errors.

5fill in blank

hard

Fill all three blanks to delete a document inside an async function with error handling.

Firebase

async function deleteUser() {
  try {
    await firestore.collection([1]).doc([2]).[3]();
  } catch (error) {
    console.error(error);
  }
}

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

A'users'

B'user789'

Cdelete

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove() instead of delete().

Not using quotes around collection or document IDs.

Use the collection name as a string, the document ID as a string, and call the delete() method to remove 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