Document-collection data model in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get a reference to a collection named 'users'.

Firebase

const usersRef = db.collection('[1]');

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

Adata

Buser

Cusers

Ddocuments

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular 'user' instead of 'users'.

Using 'documents' or 'data' which are not collection names.

The collection name must be exactly 'users' to reference the correct collection.

2fill in blank

medium

Complete the code to get a document with ID 'abc123' from the 'users' collection.

Firebase

const docRef = db.collection('users').[1]('abc123');

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

Adoc

Bget

Ccollection

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' which fetches data but does not reference a document.

Using 'collection' which is for collections, not documents.

Using 'add' which creates a new document.

The doc method is used to reference a specific document by its ID.

3fill in blank

hard

Fix the error in the code to add a new document to the 'users' collection with data.

Firebase

db.collection('users').[1]({ name: 'Alice', age: 30 });

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

Aadd

Bdoc

Cset

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'doc' which only references a document.

Using 'set' which requires a document reference first.

Using 'get' which fetches data.

The add method creates a new document with an auto-generated ID and saves the data.

4fill in blank

hard

Fill both blanks to create a document reference and set data for it.

Firebase

const docRef = db.collection('[1]').[2]('user1');
docRef.set({ active: true });

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

Ausers

Bdoc

Cposts

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'posts' instead of 'users' for the collection.

Using 'add' instead of 'doc' to get a document reference.

First, reference the 'users' collection, then get the document with ID 'user1' using doc.

5fill in blank

hard

Fill all three blanks to query documents where 'age' is greater than 25 in 'users' collection.

Firebase

const queryRef = db.collection('[1]').where('[2]', '[3]', 25);

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

Ausers

Bage

C>

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' instead of 'age' as the field.

Using '<' or '=' instead of '>' for the condition.

Using wrong collection name.

Query the 'users' collection where the field 'age' is greater than 25 using the 'where' method.

Practice

1. In Firebase's document-collection data model, what is the main container that holds documents?

easy

A. A collection

B. A table

C. A row

D. A field

Solution

1. Step 1: Understand Firebase data structure

   Firebase stores data in documents, and these documents are grouped inside collections.

2. Step 2: Identify the container for documents

   The container that holds multiple documents is called a collection, not a table, row, or field.

3. Final Answer:

   A collection -> Option A

4. Quick Check:

   Documents are inside collections [OK]

Hint: Remember: collections hold documents, like folders hold files [OK]

Common Mistakes:

• Confusing collections with tables from SQL
• Thinking documents are inside fields
• Mixing up rows with documents

2. Which of the following is the correct way to reference a document named user123 inside a collection users in Firebase?

easy

A. db.collection('users').doc('user123')

B. db.doc('users').doc('user123')

C. db.collection('user123').doc('users')

D. db.users('user123')

Solution

1. Step 1: Recall Firebase syntax for document reference

   To get a document inside a collection, use collection('name').doc('id').

2. Step 2: Match the correct syntax

   db.collection('users').doc('user123') uses db.collection('users').doc('user123'), which is the standard way.

3. Final Answer:

   db.collection('users').doc('user123') -> Option A

4. Quick Check:

   Use collection then doc to reference documents [OK]

Hint: Use collection('name').doc('id') to get a document [OK]

Common Mistakes:

• Swapping collection and doc order
• Using dot notation like db.users('user123')
• Using doc with full path incorrectly

3. Given this code snippet in Firebase:

const docRef = db.collection('books').doc('book1');
await docRef.set({ title: 'Learn Firebase', pages: 150 });
const snapshot = await db.collection('books').get();
const titles = snapshot.docs.map(doc => doc.data().title);
console.log(titles);

What will be printed in the console if the 'books' collection was empty before?

medium

A. []

B. ['book1']

C. ['Learn Firebase']

D. Error: Cannot read property 'title' of undefined

Solution

1. Step 1: Understand the code flow

   The code adds a document 'book1' with title and pages to 'books' collection, then fetches all documents in 'books'.

2. Step 2: Analyze the output of mapping titles

   Since 'books' was empty before, after adding 'book1', the collection has one document with title 'Learn Firebase'. Mapping titles returns ['Learn Firebase'].

3. Final Answer:

   ['Learn Firebase'] -> Option C

4. Quick Check:

   Added one doc, so titles list has one title [OK]

Hint: After set(), collection has that document; map titles returns it [OK]

Common Mistakes:

• Thinking snapshot is empty before set()
• Confusing document ID with title
• Expecting error due to async code

4. Consider this Firebase code snippet:

const userRef = db.collection('users').doc('user1');
userRef.get().then(doc => {
  if (doc.exists) {
    console.log(doc.data().name);
  } else {
    console.log('No such document!');
  }
});

If the document 'user1' does not exist, what will be printed?

medium

A. undefined

B. 'No such document!'

C. Error: doc.data() is undefined

D. null

Solution

1. Step 1: Check the existence condition

   The code checks if doc.exists is true before accessing data.

2. Step 2: Understand behavior when document missing

   If the document does not exist, doc.exists is false, so it prints 'No such document!'.

3. Final Answer:

   'No such document!' -> Option B

4. Quick Check:

   doc.exists false triggers else block [OK]

Hint: Check doc.exists before accessing data to avoid errors [OK]

Common Mistakes:

• Trying to access data without checking doc.exists
• Expecting undefined or null instead of message
• Confusing doc.exists with doc.data()

5. You want to store a list of users, each with multiple addresses, in Firebase. Which data model best fits this scenario?

hard

A. One document 'users' containing all users and their addresses as nested arrays

B. A single collection 'addresses' with documents containing user info and address combined

C. Multiple collections named after each user containing address documents

D. A collection 'users' with documents for each user, each containing a subcollection 'addresses' with address documents

Solution

1. Step 1: Understand hierarchical data in Firebase

   Firebase supports subcollections inside documents, which is ideal for related nested data.

2. Step 2: Choose the best structure for users and their multiple addresses

   Using a 'users' collection with each user document having an 'addresses' subcollection keeps data organized and scalable.

3. Final Answer:

   A collection 'users' with documents for each user, each containing a subcollection 'addresses' with address documents -> Option D

4. Quick Check:

   Use subcollections for nested related data [OK]

Hint: Use subcollections for nested lists like addresses per user [OK]

Common Mistakes:

• Storing all users and addresses in one big document
• Mixing user and address data in one collection without hierarchy
• Creating many collections named after users