Why write patterns affect consistency in Firebase - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to write data to Firestore with strong consistency.

Firebase

db.collection('users').doc('user1').[1]({ name: 'Alice' })

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

Adelete

Bget

Cupdate

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' which only reads data.

Using 'delete' which removes data instead of writing.

Using set writes data and ensures the document is created or overwritten, which affects consistency by making the latest data available.

2fill in blank

medium

Complete the code to perform a transaction that ensures atomic writes.

Firebase

db.runTransaction(async (transaction) => { const doc = await transaction.[1](docRef); /* update logic */ })

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

Aupdate

Bset

Cget

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' or 'update' before reading the document.

Using 'delete' which removes data instead of reading.

Within a transaction, get reads the document to ensure the transaction works with the latest data, maintaining consistency.

3fill in blank

hard

Fix the error in the code to ensure consistent writes with batch operations.

Firebase

const batch = db.batch(); batch.[1](docRef, { count: 1 }); await batch.commit();

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

Aset

Bget

Ccommit

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' which reads data instead of writing.

Calling 'commit' on the batch object instead of on the batch itself.

In batch writes, set is used to write data to a document. Using 'get' or 'commit' here is incorrect.

4fill in blank

hard

Fill both blanks to write data with merge option to avoid overwriting entire document.

Firebase

db.collection('users').doc('user2').[1]({ age: 30 }, { [2]: true })

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

Aset

Bupdate

Cmerge

Doverwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' which does not accept merge option.

Using 'overwrite' which is not a valid option.

Using set with the merge option updates only specified fields, preserving other data and improving consistency.

5fill in blank

hard

Fill all three blanks to perform a conditional update ensuring consistency.

Firebase

const doc = await db.collection('orders').doc('order1').get(); if (doc.exists && doc.data().status [1] 'pending') { await db.collection('orders').doc('order1').[2]({ status: 'completed' }, { [3]: true }); }

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

A===

Bset

Cmerge

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' or '!==' incorrectly for the condition.

Using 'update' instead of 'set' with merge option.

The code checks if the status is exactly 'pending' using ===, then uses set with merge to update the status without overwriting other fields, maintaining consistency.