Subcollections in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get a reference to a subcollection named 'orders' inside a document.

Firebase

const ordersRef = firestore.collection('users').doc('user123').[1]('orders');

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Aadd

Bdoc

Ccollection

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using doc() instead of collection() to access a subcollection

Trying to use get() or add() directly to get a reference

To access a subcollection, use collection on a document reference.

2fill in blank

medium

Complete the code to add a new document to the 'orders' subcollection.

Firebase

firestore.collection('users').doc('user123').collection('orders').[1]({ item: 'book', quantity: 1 });

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Aset

Bget

Cupdate

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using set() without a document reference

Using get() which only reads data

Use add() to create a new document with an auto-generated ID in a collection.

3fill in blank

hard

Fix the error in the code to correctly get a document from a subcollection.

Firebase

const orderDoc = firestore.collection('users').[1]('user123').collection('orders').doc('order456');

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Aadd

Bdoc

Ccollection

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using collection() instead of doc() to get a document

Using get() which fetches data, not references

Use doc() to get a specific document by ID inside a collection.

4fill in blank

hard

Fill both blanks to query all documents in the 'comments' subcollection of a post.

Firebase

const commentsQuery = firestore.collection('posts').doc('post789').[1]('comments').[2]();

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Acollection

Bdoc

Cget

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using doc() instead of collection() to access subcollection

Forgetting to call get() to fetch documents

First get the 'comments' subcollection, then call get() to fetch all documents.

5fill in blank

hard

Fill all three blanks to update a field in a document inside a subcollection.

Firebase

firestore.collection('[1]').doc('[2]').collection('[3]').doc('doc001').update({ status: 'completed' });

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Aprojects

Bproj123

Ctasks

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up collection and document names

Using wrong collection names for subcollections

Update a document in the 'tasks' subcollection of the 'proj123' document inside 'projects' collection.