Why atomic operations ensure consistency in Firebase - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to perform an atomic update on a Firestore document.

Firebase

db.collection('users').doc('user1').[1]({ age: 30 });

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

Adelete

Bget

Cset

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using set() overwrites the whole document, not atomic update.

The update method performs an atomic update on the document, ensuring consistency.

2fill in blank

medium

Complete the code to run a transaction that increments a counter atomically.

Firebase

db.runTransaction(async (transaction) => {
  const doc = await transaction.get(docRef);
  const newCount = doc.data().count + [1];
  transaction.update(docRef, { count: newCount });
});

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

A1

B-1

C0

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 does not change the count.

Using negative numbers decreases the count.

Incrementing by 1 is a common atomic operation to increase counters safely.

3fill in blank

hard

Fix the error in the transaction code to ensure atomicity.

Firebase

db.runTransaction(async (transaction) => {
  const doc = await transaction.get(docRef);
  const newBalance = doc.data().balance [1] 100;
  transaction.update(docRef, { balance: newBalance });
});

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + increases balance incorrectly.

Using * or / changes balance unexpectedly.

Subtracting 100 from the balance atomically ensures consistency when deducting funds.

4fill in blank

hard

Fill both blanks to atomically increment and check a value in Firestore.

Firebase

db.runTransaction(async (transaction) => {
  const doc = await transaction.get(docRef);
  if (doc.data().stock [1] 0) {
    transaction.update(docRef, { stock: doc.data().stock [2] 1 });
  }
});

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

A>

B+

C-

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > causes wrong condition.

Using + instead of - increases stock incorrectly.

The code checks if stock is greater than 0, then subtracts 1 atomically to reduce stock.

5fill in blank

hard

Fill all three blanks to atomically update multiple fields in a Firestore document.

Firebase

db.runTransaction(async (transaction) => {
  const doc = await transaction.get(docRef);
  transaction.update(docRef, {
    balance: doc.data().balance [1] 50,
    points: doc.data().points [2] 10,
    status: [3]
  });
});

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

A+

B-

C'active'

D'inactive'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operators changes values incorrectly.

Setting status to 'inactive' is not intended here.

The transaction adds 50 to balance, subtracts 10 from points, and sets status to 'active' atomically.