Creating collections and documents in Firebase - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new collection named 'users'.

Firebase

const usersCollection = firestore.collection('[1]');

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

Adata

Bdocuments

Citems

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong collection name like 'documents' or 'data'.

The collection name must be 'users' to create the correct collection.

2fill in blank

medium

Complete the code to add a new document with ID 'user123' to the 'users' collection.

Firebase

firestore.collection('users').doc('[1]').set({ name: 'Alice' });

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

AuserId

Buser123

CdocId

D123user

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic ID like 'userId' or a wrong ID like '123user'.

The document ID must be 'user123' to match the intended document.

3fill in blank

hard

Fix the error in the code to correctly add a document with auto-generated ID.

Firebase

firestore.collection('users').[1]({ name: 'Bob' });

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

Aadd

Bset

Cdoc

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' without specifying a document ID causes an error.

The 'add' method creates a new document with an auto-generated ID.

4fill in blank

hard

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

Firebase

const docRef = firestore.collection('[1]').doc('[2]');
docRef.set({ age: 30 });

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

Aemployees

Bemp001

Cusers

Duser001

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing collection and document names or using wrong IDs.

The collection is 'employees' and the document ID is 'emp001' as required.

5fill in blank

hard

Fill all three blanks to create a nested collection and add a document with data.

Firebase

const docRef = firestore.collection('[1]').doc('[2]').collection('[3]');
docRef.add({ status: 'active' });

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

Aprojects

BprojA

Ctasks

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong collection or document names or mixing levels.

The code creates a 'tasks' collection inside the 'projA' document of 'projects' collection.

Practice

1. What is a collection in Firebase Firestore?

easy

A. A function to add data.

B. A single document storing data.

C. A group that holds multiple documents.

D. A method to delete documents.

Solution

1. Step 1: Understand Firestore structure

   Firestore organizes data in collections and documents.

2. Step 2: Define collection role

   A collection groups multiple documents together.

3. Final Answer:

   A group that holds multiple documents. -> Option C

4. Quick Check:

   Collection = group of documents [OK]

Hint: Collections hold documents, not single data items. [OK]

Common Mistakes:

• Confusing collection with a single document
• Thinking collection is a method
• Mixing collection with data fields

2. Which Firebase Firestore method creates a document with an auto-generated ID?

easy

A. set()

B. add()

C. update()

D. get()

Solution

1. Step 1: Recall document creation methods

   Firestore uses set() to create or overwrite documents with specific IDs.

2. Step 2: Identify method for auto-generated IDs

   The add() method creates a document with an auto-generated ID inside a collection.

3. Final Answer:

   add() -> Option B

4. Quick Check:

   Auto-ID document creation = add() [OK]

Hint: Use add() for auto-generated document IDs. [OK]

Common Mistakes:

• Using set() and expecting auto-ID
• Confusing update() with creation
• Using get() which only reads data

3. What will happen when this code runs?

db.collection('users').doc('user1').set({name: 'Anna', age: 25});

medium

A. Creates or overwrites 'user1' document with name and age.

B. Adds a new document with auto-generated ID.

C. Updates only the age field in 'user1' document.

D. Throws an error because set() needs add() instead.

Solution

1. Step 1: Analyze method usage

   set() on a doc reference creates or overwrites that document.

2. Step 2: Check document ID and data

   The doc ID is 'user1', so this document will be created or replaced with given data.

3. Final Answer:

   Creates or overwrites 'user1' document with name and age. -> Option A

4. Quick Check:

   set() on doc('user1') = overwrite/create [OK]

Hint: set() replaces document at given ID, add() creates new ID. [OK]

Common Mistakes:

• Thinking add() is needed for specific IDs
• Assuming update() is called by set()
• Confusing set() with partial update

4. Identify the error in this Firestore code:

db.collection('products').add({name: 'Book', price: 10}).doc('p1').set({price: 12});

medium

A. No error, code works fine.

B. set() cannot update price field.

C. Collection name 'products' is invalid.

D. add() returns a promise, chaining doc() is invalid.

Solution

1. Step 1: Understand add() return value

   add() returns a promise resolving to a document reference, not a direct reference.

2. Step 2: Check chaining doc() after add()

   Calling doc() on the promise or document reference from add() is invalid syntax.

3. Final Answer:

   add() returns a promise, chaining doc() is invalid. -> Option D

4. Quick Check:

   add() returns promise, cannot chain doc() directly [OK]

Hint: add() returns promise; await before doc() calls. [OK]

Common Mistakes:

• Chaining doc() immediately after add()
• Ignoring promise returned by add()
• Assuming set() cannot update fields

5. You want to create a collection 'orders' and add a document with a specific ID 'order123' containing {item: 'Pen', quantity: 3}. Which code snippet is correct?

hard

A. db.collection('orders').doc('order123').set({item: 'Pen', quantity: 3});

B. db.collection('orders').add({item: 'Pen', quantity: 3, id: 'order123'});

C. db.collection('orders').doc().set({item: 'Pen', quantity: 3, id: 'order123'});

D. db.collection('orders').set('order123', {item: 'Pen', quantity: 3});

Solution

1. Step 1: Identify method to create document with specific ID

   Use doc('order123') to specify the document ID explicitly.

2. Step 2: Use set() to create or overwrite document data

   set() writes the data to the specified document ID.

3. Final Answer:

   db.collection('orders').doc('order123').set({item: 'Pen', quantity: 3}); -> Option A

4. Quick Check:

   Specific ID document creation = doc(id).set() [OK]

Hint: Use doc('id').set() for specific document IDs. [OK]

Common Mistakes:

• Using add() with id field (does not set document ID)
• Calling doc() without ID for specific ID
• Using set() directly on collection