Why databases persist data in FastAPI - Quick Recap

Recall & Review

beginner

What does it mean when we say a database 'persists data'?

It means the database saves data permanently so it stays safe even if the app or computer turns off.

beginner

Why can't we just keep data in a program's memory?

Because memory is temporary and clears when the program stops, so data would be lost without saving it somewhere permanent like a database.

beginner

How does a database help a FastAPI app with data?

It stores user info, settings, and other data safely so the app can get it anytime, even after restarting.

beginner

What is one real-life example of data persistence?

Like saving a photo on your phone gallery so you can see it later, databases save data so apps can use it later.

beginner

What happens if data is not persisted in a database?

The data disappears when the app closes, so users would lose their info or progress.

What does data persistence in a database ensure?

A Data is lost when the computer restarts

B Data is deleted when the app closes

C Data is only stored in temporary memory

D Data stays saved even after the app closes

Persistence means data remains saved and accessible after the app or system stops.

Why is storing data only in memory not enough?

A Memory clears when the app stops

B Memory is permanent

C Memory is slower than databases

D Memory can store unlimited data

Memory is temporary and clears when the app or device turns off, so data would be lost.

Which of these is a benefit of using a database with FastAPI?

A Data is saved and can be reused anytime

B Data is never saved

C Data is only stored in the browser

D Data disappears after restart

Databases save data permanently so FastAPI apps can access it anytime.

What real-life example best explains data persistence?

A Writing notes on paper and throwing them away

B Drawing on a foggy window

C Saving a photo on your phone gallery

D Speaking and forgetting words

Saving a photo means you can see it later, just like data saved in a database.

What happens if data is not persisted?

A Data is saved forever

B Data is lost when the app closes

C Data is backed up automatically

D Data is shared with other apps

Without persistence, data disappears when the app or device stops.

Explain in your own words why databases are important for saving data in apps like FastAPI.

Think about what happens if you turn off your computer without saving.

Describe a simple real-life example that helps you understand data persistence.

What do you do to keep important things safe for later?

Practice

1. Why do databases persist data in applications like FastAPI?

easy

A. To keep data safe even if the app stops or restarts

B. To make the app run faster

C. To delete old data automatically

D. To prevent users from accessing the app

Solution

1. Step 1: Understand what persistence means

   Persistence means data stays saved even after the program stops running.

2. Step 2: Connect persistence to databases in FastAPI

   Databases store data on disk, so FastAPI can retrieve it later, even after restarts.

3. Final Answer:

   To keep data safe even if the app stops or restarts -> Option A

4. Quick Check:

   Persistence means data stays saved [OK]

Hint: Persistence means data stays saved after app stops [OK]

Common Mistakes:

• Thinking databases speed up the app only
• Confusing persistence with data deletion
• Believing databases block user access

2. Which of the following is the correct way to save data to a database in FastAPI?

easy

A. Use a database session to add and commit the data

B. Print the data to the console

C. Store data in a local variable only

D. Use a global variable to hold data

Solution

1. Step 1: Identify how FastAPI interacts with databases

   FastAPI uses database sessions to add and commit data to save it permanently.

2. Step 2: Compare options for saving data

   Printing or using variables does not save data persistently; only committing via session does.

3. Final Answer:

   Use a database session to add and commit the data -> Option A

4. Quick Check:

   Commit data with session to save [OK]

Hint: Commit data with session to save persistently [OK]

Common Mistakes:

• Thinking printing saves data
• Using variables instead of database commit
• Skipping the commit step

3. Given this FastAPI code snippet, what will happen when the app restarts?

from fastapi import FastAPI
from sqlalchemy.orm import Session

app = FastAPI()

@app.post('/items/')
def create_item(session: Session, item: Item):
    session.add(item)
    session.commit()
    return item

medium

A. The items will be saved only in memory

B. The saved items will be lost after restart

C. The app will crash on restart

D. The saved items will still be available after restart

Solution

1. Step 1: Understand what session.commit() does

   Calling commit() saves data permanently to the database storage.

2. Step 2: Consider app restart effect on database data

   Since data is saved in the database, it remains after the app restarts.

3. Final Answer:

   The saved items will still be available after restart -> Option D

4. Quick Check:

   Committed data persists after restart [OK]

Hint: Committed data stays after app restarts [OK]

Common Mistakes:

• Confusing commit with temporary memory storage
• Assuming app restart clears database
• Thinking session.add alone saves data

4. What is wrong with this FastAPI code that tries to save data?

from fastapi import FastAPI

app = FastAPI()

@app.post('/users/')
def create_user(user: dict):
    user['id'] = 1
    return user

medium

A. It uses the wrong HTTP method

B. It does not save data to a database, so data is lost on restart

C. It has a syntax error in the function

D. It commits data twice

Solution

1. Step 1: Check if data is saved to a database

   The code only modifies and returns a dictionary; it does not save to any database.

2. Step 2: Understand consequence of no database saving

   Without saving to a database, data is lost when the app stops or restarts.

3. Final Answer:

   It does not save data to a database, so data is lost on restart -> Option B

4. Quick Check:

   No database save means no persistence [OK]

Hint: Data must be saved to database for persistence [OK]

Common Mistakes:

• Thinking returning dict saves data
• Confusing HTTP method with persistence
• Assuming syntax error when none exists

5. You want to ensure user data is saved permanently in FastAPI. Which approach correctly combines FastAPI and database persistence?

hard

A. Store user data in a global list variable inside the app

B. Save user data only in request body without database interaction

C. Use FastAPI with SQLAlchemy session to add and commit user data to a database

D. Print user data to console and rely on logs for storage

Solution

1. Step 1: Identify how to save data permanently

   Permanent saving requires writing data to a database, not just memory or logs.

2. Step 2: Match FastAPI with database usage

   FastAPI works well with SQLAlchemy sessions to add and commit data to databases.

3. Step 3: Eliminate incorrect options

   Global variables and printing do not persist data after app stops; request body alone is temporary.

4. Final Answer:

   Use FastAPI with SQLAlchemy session to add and commit user data to a database -> Option C

5. Quick Check:

   Database commit ensures permanent data [OK]

Hint: Use database session commit for permanent save [OK]

Common Mistakes:

• Using global variables for persistence
• Relying on request data without saving
• Thinking console logs save data