Document ID strategies in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new document with a specific ID in Firestore.

Firebase

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

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

A'user123'

Bdb.collection('users').doc().id

Cdb.collection('users').doc().autoId()

Ddb.collection('users').doc().id()

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to get an auto-generated ID by calling a method on doc() that doesn't exist.

Passing a method call instead of a string as the document ID.

To create a document with a specific ID, you pass the ID as a string to doc(). Auto-generated IDs require a different method.

2fill in blank

medium

Complete the code to add a new document with an auto-generated ID in Firestore.

Firebase

db.collection('orders').[1]({item: 'book', quantity: 1});

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

Aset

Bdoc

Cadd

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using doc() without arguments but forgetting to call set().

Using set() directly on the collection, which is invalid.

The add() method adds a new document with an auto-generated ID to the collection.

3fill in blank

hard

Fix the error in the code to generate a unique document ID before setting data.

Firebase

const newDocRef = db.collection('products').[1]();
newDocRef.set({name: 'Pen', price: 1.5});

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

Adoc

Bdoc('uniqueId')

Cadd()

Dset()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling add() on the collection and then trying to call set() on the result.

Passing a string to doc() when you want an auto-generated ID.

Calling doc() without arguments creates a reference with a unique auto-generated ID. Then you can call set() on it.

4fill in blank

hard

Fill both blanks to create a document with a custom ID and set data in Firestore.

Firebase

const customId = [1];
db.collection('customers').doc(customId).[2]({email: '[e-mail]'});

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

A'cust_001'

Badd

Cset

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using add() instead of set() when specifying a custom ID.

Passing a variable instead of a string literal for the custom ID.

You assign a string as a custom ID, then call set() on the document reference to save data.

5fill in blank

hard

Fill all three blanks to generate a new document ID, get its ID string, and set data in Firestore.

Firebase

const newDoc = db.collection('invoices').[1]();
const docId = newDoc.[2];
newDoc.[3]({total: 100});

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

Adoc

Bid

Cset

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using add() instead of doc() when needing the document ID before setting data.

Trying to call id() as a function instead of accessing the property.

Use doc() to create a new document reference with an auto-generated ID, access the ID with id, and save data with set().

Practice

1. What is the main purpose of a document ID in Firebase?

easy

A. To uniquely identify each record in a collection

B. To store user passwords securely

C. To define the database location

D. To control access permissions

Solution

1. Step 1: Understand what a document ID represents

   A document ID is a unique identifier for each record in a Firebase collection, ensuring each document can be accessed individually.

2. Step 2: Differentiate from other database concepts

   Document IDs are not used for storing passwords, defining database location, or controlling access permissions.

3. Final Answer:

   To uniquely identify each record in a collection -> Option A

4. Quick Check:

   Document ID = Unique record identifier [OK]

Hint: Document ID uniquely names each record [OK]

Common Mistakes:

• Confusing document ID with security rules
• Thinking document ID stores data
• Mixing document ID with database path

2. Which of the following is the correct way to let Firebase generate a document ID automatically?

easy

A. Use collectionRef.doc() without arguments

B. Use collectionRef.doc('customID')

C. Use collectionRef.add(data)

D. Use collectionRef.set(data)

Solution

1. Step 1: Identify Firebase methods for adding documents

   The add() method adds a document with an auto-generated ID to a collection.

2. Step 2: Understand difference from doc() and set()

   doc() with no argument creates a reference but does not add data; set() requires a document reference.

3. Final Answer:

   Use collectionRef.add(data) -> Option C

4. Quick Check:

   Auto ID creation = add() method [OK]

Hint: Use add() to auto-generate document ID [OK]

Common Mistakes:

• Using doc() without set() does not create document
• Assuming set() auto-generates ID
• Passing custom ID when auto ID is needed

3. Given this code snippet, what will be the document ID of the new document?

const docRef = collectionRef.doc('user123');
docRef.set({name: 'Alice'});

medium

A. 'user123'

B. Auto-generated random ID

C. 'Alice'

D. Undefined

Solution

1. Step 1: Analyze the doc() method argument

   The doc('user123') call creates a document reference with ID 'user123'.

2. Step 2: Understand set() usage

   The set() method writes data to the document with the specified ID.

3. Final Answer:

   'user123' -> Option A

4. Quick Check:

   doc('user123') sets document ID = 'user123' [OK]

Hint: doc('ID') sets document ID explicitly [OK]

Common Mistakes:

• Thinking set() changes the ID
• Assuming ID is auto-generated here
• Confusing document data with ID

4. What is wrong with this code if the goal is to create a document with an auto-generated ID?

const docRef = collectionRef.doc();

medium

A. doc() requires a string argument

B. doc() without arguments does not create a document automatically

C. set() cannot be used with doc()

D. The data object is missing an ID field

Solution

1. Step 1: Understand doc() without arguments

   Calling doc() without arguments creates a reference with a random ID but does not create the document automatically.

2. Step 2: Confirm the issue

   The code only creates a DocumentReference; to create the document, set(data) or add(data) is needed.

3. Final Answer:

   doc() without arguments does not create a document automatically -> Option B

4. Quick Check:

   doc() alone ≠ document creation [OK]

Hint: doc() alone doesn't create document, set() must follow [OK]

Common Mistakes:

• Assuming doc() creates document immediately
• Thinking set() is invalid here
• Expecting doc() to require argument always

5. You want to create user profiles with document IDs matching their usernames for easy lookup. Which strategy is best?

hard

A. Create documents without IDs and rely on collection order

B. Let Firebase auto-generate IDs and store username inside document

C. Use random UUIDs as document IDs and index usernames separately

D. Use usernames as document IDs by calling doc(username)

Solution

1. Step 1: Understand the goal

   The goal is to have document IDs that match usernames for easy direct lookup.

2. Step 2: Evaluate strategies

   Using doc(username) sets the document ID to the username, enabling direct access by username.

3. Step 3: Compare with other options

   Auto-generated IDs or random UUIDs require extra queries to find username; no IDs or relying on order is unreliable.

4. Final Answer:

   Use usernames as document IDs by calling doc(username) -> Option D

5. Quick Check:

   Username as ID = direct lookup [OK]

Hint: Use username as doc ID for direct access [OK]

Common Mistakes:

• Relying on auto IDs for username lookup
• Ignoring need for unique IDs
• Assuming collection order is stable