Firestore collections and documents in GCP - Commands & Configuration

Introduction

Firestore is a database that stores data in collections and documents. Collections are like folders, and documents are like files inside those folders. This helps organize and find data easily.

When you want to save user profiles for a mobile app.

When you need to store messages in a chat application.

When you want to keep track of products in an online store.

When you want to organize blog posts and their comments.

When you need a flexible database that grows with your app.

Commands

This command creates a Firestore database in the us-central1 region. You need a database before adding collections and documents.

Terminal

gcloud firestore databases create --region=us-central1

Expected Output

Created Firestore database (default) in region us-central1.

→

--region - Specifies the location for the Firestore database.

This command creates a document with ID 'user123' inside the 'users' collection. The document stores a name and age.

Terminal

gcloud firestore documents create users/user123 --data='{"name":"Alice","age":30}'

Expected Output

Created document users/user123.

→

--data - Provides the JSON data to store in the document.

This command retrieves the document with ID 'user123' from the 'users' collection to check its contents.

Terminal

gcloud firestore documents get users/user123

Expected Output

{

  "name": "Alice",

  "age": 30

}

This command lists all documents inside the 'users' collection to see what user records exist.

Terminal

gcloud firestore documents list users

Expected Output

users/user123

Key Concept

If you remember nothing else from this pattern, remember: Firestore organizes data in collections (like folders) and documents (like files) to keep data neat and easy to find.

Common Mistakes

Trying to create a document before creating the Firestore database.

Firestore needs a database to exist before you can add collections or documents.

Always create the Firestore database first using the create command.

Using incorrect JSON format in the --data flag when creating a document.

Invalid JSON causes the command to fail and the document won't be created.

Use proper JSON syntax with double quotes and no trailing commas.

Confusing collection names and document IDs in commands.

Commands require the correct path format: collection/document. Mixing them causes errors.

Always specify collection first, then document ID, separated by a slash.

Summary

Create a Firestore database in a chosen region before adding data.

Add documents inside collections using JSON data to store information.

Retrieve and list documents to verify and manage stored data.

Practice

1. What is the correct way to describe Firestore's data structure?

easy

A. Documents are the top-level containers holding collections.

B. Documents contain collections, and collections contain key-value pairs.

C. Collections contain key-value pairs directly without documents.

D. Collections contain documents, and documents contain key-value pairs.

Solution

1. Step 1: Understand Firestore data hierarchy

   Firestore organizes data with collections at the top level, which hold documents.

2. Step 2: Identify what documents contain

   Documents store data as key-value pairs, not collections directly.

3. Final Answer:

   Collections contain documents, and documents contain key-value pairs. -> Option D

4. Quick Check:

   Firestore data = collections > documents > key-value pairs [OK]

Hint: Remember: Collections hold documents, documents hold data [OK]

Common Mistakes:

• Thinking documents hold collections directly
• Assuming collections store key-value pairs without documents
• Confusing the order of collections and documents

2. Which of the following is the correct syntax to get a reference to a document named user123 inside a collection users in Firestore using Node.js?

easy

A. const docRef = firestore.doc('user123/users');

B. const docRef = firestore.collection('users').doc('user123');

C. const docRef = firestore.collection('user123').doc('users');

D. const docRef = firestore.doc('users').doc('user123');

Solution

1. Step 1: Identify correct method to access collection and document

   Use collection('users') to access the collection, then doc('user123') to get the document.

2. Step 2: Check path correctness

   Direct firestore.doc(full/path) works for existing paths, but incorrect paths, reversed order, or misusing doc() on document references fail. Chaining collection().doc() is recommended.

3. Final Answer:

   const docRef = firestore.collection('users').doc('user123'); -> Option B

4. Quick Check:

   Use collection().doc() chaining for document refs [OK]

Hint: Chain collection() then doc() for document reference [OK]

Common Mistakes:

• Swapping collection and document names
• Using firestore.doc() with incorrect path format
• Confusing collection() and doc() order

3. Given the following Firestore code snippet, what will be the output if the document user123 exists with fields {name: 'Alice', age: 30}?

const docRef = firestore.collection('users').doc('user123');
const docSnap = await docRef.get();
if (docSnap.exists) {
  console.log(docSnap.data());
} else {
  console.log('No such document!');
}

medium

A. 'No such document!'

B. undefined

C. { name: 'Alice', age: 30 }

D. Error: Document not found

Solution

1. Step 1: Check if document exists

   The code checks docSnap.exists, which is true if the document is present.

2. Step 2: Output document data

   If exists, docSnap.data() returns the document fields as an object.

3. Final Answer:

   { name: 'Alice', age: 30 } -> Option C

4. Quick Check:

   docSnap.exists true means data() returns fields [OK]

Hint: docSnap.exists true means data() returns document fields [OK]

Common Mistakes:

• Assuming data() returns undefined if document exists
• Confusing exists check with data presence
• Expecting error instead of 'No such document!' message

4. You wrote this Firestore code to get a document but docSnap.exists is false:

const docRef = firestore.collection('users').doc();
const docSnap = await docRef.get();

What is the problem?

medium

A. Missing document ID in doc() causes a reference to a non-existing document.

B. You cannot call get() on a document reference.

C. Collection name 'users' is invalid without quotes.

D. You must use firestore.doc() instead of collection().doc().

Solution

1. Step 1: Check doc() usage

   Calling doc() without an ID creates a reference to a new document with an auto-generated ID, but it does not exist yet.

2. Step 2: Understand get() on new doc reference

   Trying to get() returns a snapshot with exists=false because the document does not exist.

3. Final Answer:

   Missing document ID in doc() causes a reference to a non-existing document. -> Option A

4. Quick Check:

   doc() needs ID to get existing document [OK]

Hint: Always provide document ID in doc() to read existing document [OK]

Common Mistakes:

• Assuming doc() without ID points to existing document
• Thinking get() cannot be called on document references
• Confusing collection and document method usage

5. You want to store user profiles in Firestore where each user has multiple addresses. Which is the best Firestore structure to model this data?

hard

A. A collection 'users' with documents for each user, and each user document has a subcollection 'addresses' with address documents.

B. A single collection 'addresses' with documents containing user info and address fields combined.

C. A collection 'users' where each document stores all addresses as a large array field.

D. Multiple collections named after each user ID, each containing address documents.

Solution

1. Step 1: Understand Firestore best practice for one-to-many

   Use a main collection for users, and subcollections for related multiple items like addresses.

2. Step 2: Evaluate options

   A collection 'users' with documents for each user, and each user document has a subcollection 'addresses' with address documents. uses subcollections for addresses, which is scalable and organized. A single collection 'addresses' with documents containing user info and address fields combined. mixes user and address data in one collection, which is less clear. A collection 'users' where each document stores all addresses as a large array field. stores all addresses in one field, which can be inefficient. Multiple collections named after each user ID, each containing address documents. creates many collections dynamically, which is not recommended.

3. Final Answer:

   A collection 'users' with documents for each user, and each user document has a subcollection 'addresses' with address documents. -> Option A

4. Quick Check:

   Use subcollections for related multiple items [OK]

Hint: Use subcollections for multiple related documents per user [OK]

Common Mistakes:

• Storing multiple addresses in one array field causing size limits
• Creating dynamic collections per user causing management issues
• Mixing unrelated data in one collection