Firestore document model in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Firestore document?

A Firestore document is a single record in a Firestore database. It stores data as key-value pairs and is similar to a row in a table but more flexible.

beginner

How are Firestore documents organized?

Documents are organized into collections. Each collection contains multiple documents, and documents can contain subcollections, creating a tree-like structure.

intermediate

Can Firestore documents contain nested data?

Yes, documents can contain nested objects and arrays as values, allowing complex data structures inside a single document.

intermediate

What is the maximum size of a Firestore document?

A Firestore document can be up to 1 MiB (1,048,576 bytes) in size, including all fields and nested data.

beginner

How does Firestore handle document IDs?

Each document has a unique ID within its collection. IDs can be auto-generated by Firestore or set manually by the user.

What is the basic unit of data storage in Firestore?

A Table

B Document

C Row

D Bucket

Firestore stores data in documents, which are the basic units of data storage.

How are documents grouped in Firestore?

A In collections

B In tables

C In buckets

D In rows

Documents are grouped into collections in Firestore.

What is the maximum size allowed for a Firestore document?

A 5 MiB

B 10 MiB

C 1 MiB

D 100 KiB

Firestore documents can be up to 1 MiB in size.

Can Firestore documents contain arrays and nested objects?

A Yes

B No

C Only arrays

D Only nested objects

Firestore documents support both arrays and nested objects.

How are document IDs assigned in Firestore?

A By collection name

B Only manually

C Only auto-generated

D Manually or auto-generated

Document IDs can be set manually or auto-generated by Firestore.

Explain how Firestore organizes data using documents and collections.

Think of folders (collections) containing files (documents).

Describe the types of data Firestore documents can hold and any size limits.

Consider what fits inside a single document.

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