Document ID strategies in Firebase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Document ID in Firebase Firestore?

A Document ID is a unique identifier for each document in a Firestore collection. It helps to find, update, or delete that specific document.

beginner

What are the two main ways to create Document IDs in Firestore?

You can either let Firestore auto-generate a random unique ID or create your own custom ID based on your app's needs.

intermediate

Why might you choose to use custom Document IDs instead of auto-generated ones?

Custom IDs can make documents easier to find and organize if they follow a meaningful pattern, like user emails or product codes.

intermediate

What is a risk of using predictable Document IDs?

Predictable IDs can lead to security risks if unauthorized users guess IDs and access data they shouldn’t see.

advanced

How does Firestore generate auto IDs?

Firestore creates a 20-character string with random letters and numbers to ensure uniqueness and avoid collisions.

What does Firestore use as a Document ID if you don't specify one?

A A random unique string

B The current timestamp

C The user's email address

D A sequential number

Firestore auto-generates a random unique string as the Document ID if you don't provide one.

Which of these is a benefit of using custom Document IDs?

A Prevents data loss

B Easier to remember and organize documents

C Faster database queries

D Automatically more secure

Custom IDs can be meaningful and easier to remember or organize, but they don't automatically improve security or speed.

What is a potential downside of using predictable Document IDs?

A They slow down the database

B They take more storage space

C They can be guessed by unauthorized users

D They cause data duplication

Predictable IDs can be guessed, which may expose data to unauthorized access.

How long is a Firestore auto-generated Document ID?

A 20 characters

B 10 characters

C 32 characters

D 8 characters

Firestore generates a 20-character string for auto IDs to ensure uniqueness.

Which strategy is best when you need to reference documents by a known key like a username?

A Use auto-generated Document IDs

B Use random numbers as Document IDs

C Use timestamps as Document IDs

D Use custom Document IDs

Custom Document IDs let you use meaningful keys like usernames for easy reference.

Explain the difference between auto-generated and custom Document IDs in Firestore.

Think about how Firestore creates IDs and why you might want to choose your own.

Describe a scenario where using custom Document IDs might cause security concerns.

Consider what happens if someone guesses a document's ID.

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