Firestore document model in GCP - Step-by-Step Execution

Process Flow - Firestore document model

Start: Create Collection

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Add Document with ID

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Add Fields (key-value pairs)

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Document Stored in Collection

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Query or Update Document

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End

This flow shows how you create a collection, add a document with fields, and then store or query it in Firestore.

Execution Sample

GCP

collection = 'users'
doc_id = 'user123'
document = {'name': 'Alice', 'age': 30}
firestore.collection(collection).document(doc_id).set(document)

This code creates a 'users' collection, adds a document with ID 'user123' containing name and age fields.

Process Table

Step	Action	Input	Result	State Change
1	Create collection reference	'users'	Collection 'users' ready	Collection 'users' created
2	Create document reference	'user123'	Document ref 'user123' ready	Document ref 'user123' created in 'users'
3	Prepare document data	{'name': 'Alice', 'age': 30}	Data ready to store	Data prepared with fields name and age
4	Set document in Firestore	Document ref + data	Document stored in 'users/user123'	Firestore now has document 'user123' with fields
5	Query document	'users/user123'	Returns {'name': 'Alice', 'age': 30}	Document data retrieved
6	Update document field	Set age=31	Document updated	Field 'age' changed to 31
7	Query updated document	'users/user123'	Returns {'name': 'Alice', 'age': 31}	Updated data retrieved
8	End	-	-	Process complete

💡 Process ends after document is created, updated, and queried successfully.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	Final
collection	undefined	'users'	'users'	'users'	'users'
doc_id	undefined	'user123'	'user123'	'user123'	'user123'
document	undefined	{'name': 'Alice', 'age': 30}	{'name': 'Alice', 'age': 30}	{'name': 'Alice', 'age': 31}	{'name': 'Alice', 'age': 31}
firestore state	empty	empty	has 'users/user123' with fields	has 'users/user123' with updated age	has 'users/user123' with updated age

Key Moments - 3 Insights

Why do we need to specify a document ID when adding a document?

Specifying a document ID (see Step 2) lets you control the document's address in the collection. Without it, Firestore creates a random ID, which can make it harder to find or update later.

What happens if we update a field in the document?

Updating a field (Step 6) changes only that field's value in Firestore. The rest of the document stays the same, as shown by the variable_tracker where 'age' changes but 'name' remains.

Can a document exist without fields?

No, a document must have at least one field. In Step 3, we prepare fields before storing. Firestore requires data to store a document.

Visual Quiz - 3 Questions

Look at the execution table, what is the document data after Step 4?

A {'name': 'Alice', 'age': 31}

B {}

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

D No data stored yet

💡 Hint

Check the 'Result' column at Step 4 in the execution_table.

At which step does the 'age' field get updated to 31?

A Step 6

B Step 4

C Step 3

D Step 7

💡 Hint

Look at the 'Action' and 'State Change' columns in the execution_table for field updates.

If we do not specify a document ID, what changes in the execution flow?

A Step 4 fails to store the document

B Step 2 is skipped and Firestore generates a random ID

C Step 3 changes the document data

D No document is created

💡 Hint

Refer to Step 2 in the execution_table about document reference creation.

Concept Snapshot

Firestore Document Model:
- Collections hold documents.
- Documents have unique IDs and fields (key-value pairs).
- Create a collection, then add a document with fields.
- Update fields without replacing whole document.
- Query documents by collection and ID.

Full Transcript

This visual execution shows how Firestore stores data using collections and documents. First, a collection named 'users' is created. Then a document with ID 'user123' is prepared with fields 'name' and 'age'. This document is stored in Firestore under the 'users' collection. Later, the document is queried and the 'age' field is updated from 30 to 31. Each step updates the Firestore state and variables accordingly. Key points include the importance of document IDs, how fields are updated individually, and that documents must have fields to exist.