Firestore document model in GCP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Firestore document reference.

GCP

doc_ref = db.collection('users').[1]('user123')

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

Adocument

Badd

Cget

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' which retrieves data instead of referencing a document.

Using 'add' which adds a new document instead of referencing an existing one.

The document method creates a reference to a specific document in a collection.

2fill in blank

medium

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

GCP

db.collection('orders').[1]({'item': 'book', 'qty': 3})

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

Aupdate

Bset

Cadd

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' which requires a document reference.

Using 'update' which only modifies existing documents.

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 update a document field.

GCP

db.collection('products').doc('prod1').[1]({'price': 20})

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

Aset

Bupdate

Cadd

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' which creates a new document instead of updating.

Using 'set' which overwrites the whole document.

The update method modifies specific fields of an existing document without overwriting the whole document.

4fill in blank

hard

Fill both blanks to query documents where age is greater than 25.

GCP

results = db.collection('employees').where('age', [1], [2]).get()

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

A==

B>

C25

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which only matches exact values.

Using '<' which finds ages less than 25.

The where method filters documents. Use '>' to find ages greater than 25.

5fill in blank

hard

Fill all three blanks to create a dictionary of user names and their emails for users older than 30.

GCP

user_emails = {user.[1]: user.[2] for user in users if user.[3] > 30}

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

Aname

Bemail

Cage

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' instead of 'name' for keys.

Filtering by 'email' instead of 'age'.

This dictionary comprehension maps user names to emails only if their age is over 30.

Practice

1. What is the basic unit of data storage in Firestore?

easy

A. A table

B. A document

C. A bucket

D. A file

Solution

1. Step 1: Understand Firestore data structure

   Firestore organizes data into collections and documents, not tables or files.

2. Step 2: Identify the smallest data unit

   The smallest unit is a document, which holds fields and values.

3. Final Answer:

   A document -> Option B

4. Quick Check:

   Firestore stores data as documents [OK]

Hint: Remember: Firestore uses documents, not tables or files [OK]

Common Mistakes:

• Confusing documents with tables from SQL databases
• Thinking Firestore stores files like Cloud Storage
• Assuming buckets are data units in Firestore

2. Which of the following is the correct way to represent a Firestore document field in JSON-like syntax?

easy

A. "name": "Alice"

B. "name" = "Alice"

C. name: Alice

D. 'name' -> 'Alice'

Solution

1. Step 1: Recall JSON field syntax

   JSON uses double quotes for keys and string values, separated by a colon.

2. Step 2: Match Firestore document field style

   Firestore documents resemble JSON, so the correct syntax is "key": "value".

3. Final Answer:

   "name": "Alice" -> Option A

4. Quick Check:

   Firestore fields use JSON syntax [OK]

Hint: Use colon and double quotes for Firestore fields [OK]

Common Mistakes:

• Using equals sign instead of colon
• Omitting quotes around keys or values
• Using arrow notation which is invalid

3. Given a Firestore collection 'users' with documents having fields {"age": 30, "active": true}, what will the query return if you filter for documents where active == false?

medium

A. All documents with active false

B. All documents regardless of active field

C. Error due to invalid filter

D. No documents

Solution

1. Step 1: Understand the data and filter condition

   Documents have "active": true, but the query filters for active == false.

2. Step 2: Evaluate query result

   No documents match active == false, so the query returns no results.

3. Final Answer:

   No documents -> Option D

4. Quick Check:

   Filter matches no documents [OK]

Hint: Filter matches only exact values; no match means empty result [OK]

Common Mistakes:

• Assuming query returns all documents
• Expecting an error for valid filter
• Confusing true and false values

4. You try to add a document with this data: {name: "Bob", age: "twenty"}. What is the likely issue?

medium

A. Firestore requires age to be a number, not a string

B. No issue, document will be added

C. Field names must be in quotes

D. Document ID is missing

Solution

1. Step 1: Check field name syntax

   Firestore expects field names as strings in JSON, so keys must be quoted.

2. Step 2: Analyze the given data

   Keys are unquoted (name, age), which is invalid JSON syntax for Firestore.

3. Final Answer:

   Field names must be in quotes -> Option C

4. Quick Check:

   Field names need quotes in Firestore JSON [OK]

Hint: Always quote field names in Firestore documents [OK]

Common Mistakes:

• Thinking Firestore auto-corrects missing quotes
• Assuming string values for numbers cause errors
• Believing document ID is mandatory in data

5. You want to model a blog app in Firestore. Each blog post has multiple comments. Which is the best Firestore document model to organize this data?

hard

A. Create a 'posts' collection with documents for each post, and a subcollection 'comments' inside each post document

B. Store all comments as an array field inside each blog post document

C. Create a single collection 'comments' with a field referencing the post ID

D. Store all posts and comments in one flat collection

Solution

1. Step 1: Consider Firestore best practices for related data

   Large or growing lists like comments should be in subcollections, not arrays, for scalability.

2. Step 2: Evaluate options for organizing posts and comments

   Using a 'posts' collection with 'comments' subcollections keeps data organized and efficient.

3. Final Answer:

   Create a 'posts' collection with documents for each post, and a subcollection 'comments' inside each post document -> Option A

4. Quick Check:

   Use subcollections for related many items [OK]

Hint: Use subcollections for many related items, not arrays [OK]

Common Mistakes:

• Putting all comments in one array causing size limits
• Using a flat collection losing post-comment grouping
• Referencing post ID without subcollections complicates queries