Why databases persist data in FastAPI - See It in Action

Why Databases Persist Data

📖 Scenario: You are building a simple FastAPI app to store and retrieve user notes. This app will show how data is saved persistently using a database instead of temporary memory.

🎯 Goal: Create a FastAPI app that saves notes in a dictionary and then add a configuration to simulate saving notes persistently. Finally, implement a route to add notes and a route to get all saved notes.

📋 What You'll Learn

Create a dictionary called notes_db to store notes with keys as note IDs and values as note texts

Add a variable called next_id starting at 1 to assign unique IDs to notes

Write a POST route /add_note that accepts a note text and saves it in notes_db with the current next_id, then increments next_id

Write a GET route /notes that returns all saved notes from notes_db

💡 Why This Matters

🌍 Real World

Many web apps need to save user data like notes, messages, or profiles so it stays available after the app restarts or users come back later.

💼 Career

Understanding how to persist data is essential for backend developers building APIs and services that manage user data reliably.

1

Create the initial data structure

Create a dictionary called notes_db initialized as empty and a variable called next_id set to 1 to hold note IDs.

FastAPI

# Create notes_db dictionary and next_id variable
# Your code here

Need a hint?

Use notes_db = {} to create an empty dictionary and next_id = 1 to start IDs from 1.

2

Add configuration variable

Add a FastAPI app instance called app by importing FastAPI and creating app = FastAPI().

FastAPI

notes_db = {}
next_id = 1

# Create FastAPI app instance
# Your code here

Need a hint?

Import FastAPI and create an app instance with app = FastAPI().

3

Implement core logic to add notes

Write a POST route /add_note using @app.post("/add_note") that accepts a JSON body with a text field. Inside the function, add the note text to notes_db with the current next_id as key, then increment next_id by 1. Return the note ID in the response.

FastAPI

from fastapi import FastAPI

notes_db = {}
next_id = 1

app = FastAPI()

# Add POST route to add notes
# Your code here

Need a hint?

Use @app.post("/add_note") decorator and an async function that reads JSON from the request. Use global next_id to modify the variable.

4

Add route to get all notes

Write a GET route /notes using @app.get("/notes") that returns the entire notes_db dictionary.

FastAPI

from fastapi import FastAPI, Request

notes_db = {}
next_id = 1

app = FastAPI()

@app.post("/add_note")
async def add_note(request: Request):
    global next_id
    data = await request.json()
    text = data.get("text")
    notes_db[next_id] = text
    note_id = next_id
    next_id += 1
    return {"note_id": note_id}

# Add GET route to return all notes
# Your code here

Need a hint?

Use @app.get("/notes") decorator and return the notes_db dictionary directly.