Why databases persist data in FastAPI - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the FastAPI class.

FastAPI

from fastapi import [1]
app = FastAPI()

Drag options to blanks, or click blank then click option'

ADepends

BFastAPI

CResponse

DRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request or Response instead of FastAPI.

The FastAPI class is imported to create the app instance.

2fill in blank

medium

Complete the code to define a GET route that returns a welcome message.

FastAPI

@app.[1]("/")
async def root():
    return {"message": "Welcome!"}

Drag options to blanks, or click blank then click option'

Aget

Bpost

Cput

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using post or put instead of get for a simple retrieval.

The GET method is used to retrieve data from the server.

3fill in blank

hard

Fix the error in the code to connect to a SQLite database using SQLAlchemy.

FastAPI

from sqlalchemy import create_engine
engine = create_engine("sqlite:///[1]")

Drag options to blanks, or click blank then click option'

Adatabase.db

Bdb.sqlite3

C:memory:

Dmemory

Attempts:

3 left

💡 Hint

Common Mistakes

Using :memory: creates a temporary in-memory database, not persistent.

The database file name must be specified correctly for SQLite connection.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that stores word lengths for words longer than 3 characters.

FastAPI

{word: [1] for word in words if len(word) [2] 3}

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Alen(word)

B==

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality or less than instead of greater than for filtering.

The dictionary stores the length of each word, but only for words longer than 3 characters.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that stores uppercase keys and values for items with positive values.

FastAPI

result = [1]: [2] for k, v in data.items() if v [3] 0}

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Ak.upper()

Bv

C>

Dk.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using k.lower() or wrong comparison operators.

The comprehension creates a dictionary with uppercase keys and their values only if the value is positive.

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