Creating collections and documents in Firebase - Practice Exercises

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when you add a document without specifying an ID?

In Firebase Firestore, if you add a document to a collection without specifying an ID, what will be the result?

Firebase

db.collection('users').add({name: 'Alice', age: 30});

A Firestore automatically generates a unique ID for the new document.

B The document is added with an empty string as its ID.

C The operation fails with an error because ID is required.

D The document overwrites the first document in the collection.

💡 Hint

Think about how Firestore handles document IDs when none are provided.

When you use add() without an ID, Firestore creates a unique ID automatically to avoid conflicts.

❓ Configuration

intermediate

Which code snippet correctly creates a collection and a document with a custom ID?

Choose the code that creates a collection named products and adds a document with ID prod123 containing a field price set to 100.

A db.collection('products').doc().set({id: 'prod123', price: 100});

B db.collection('products').add({id: 'prod123', price: 100});

C db.collection('products').doc('prod123').set({price: 100});

D db.doc('products/prod123').add({price: 100});

💡 Hint

Remember that doc() with an argument sets the document ID explicitly.

Using doc('prod123') sets the document ID to prod123. Then set() adds the data.

❓ Architecture

advanced

How does Firestore organize data when you create nested collections?

Consider you have a collection users, each user document has a subcollection orders. How is this data organized in Firestore?

A Subcollections are separate collections linked by path, not nested inside documents.

B Each <code>orders</code> subcollection is stored inside its parent user document as a nested object.

C All subcollections are merged into the main <code>users</code> collection.

D Firestore duplicates subcollection data inside the parent document for faster access.

💡 Hint

Think about how Firestore paths work for collections and documents.

Firestore stores subcollections as separate collections identified by their path under a document, not nested inside the document data.

❓ security

advanced

Which Firestore security rule allows only authenticated users to create documents in the 'messages' collection?

Choose the correct Firestore security rule snippet that permits only signed-in users to add documents to the messages collection.

A match /messages/{msgId} { allow create: if request.auth == null; }

B match /messages/{msgId} { allow create: if request.auth != null; }

C match /messages/{msgId} { allow create: if true; }

D match /messages/{msgId} { allow create: if request.auth.uid == ''; }

💡 Hint

Check how to verify if a user is signed in using request.auth.

The condition request.auth != null ensures the user is authenticated before allowing create.

✅ Best Practice

expert

What is the best practice for structuring Firestore collections to optimize read performance for user profiles and their posts?

You want to design Firestore data for users and their posts. Which approach optimizes read performance and scalability?

A Duplicate posts data inside both user documents and a posts collection.

B Store all posts as a subcollection under each user document.

C Embed all posts inside the user document as an array.

D Store all posts in a single top-level collection with a userId field to filter posts.

💡 Hint

Consider Firestore limits on document size and query efficiency.

Storing posts in a top-level collection with a userId field allows efficient queries and avoids document size limits.