Async database queries in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an async function in FastAPI.

FastAPI

async def [1]():
    return {"message": "Hello"}

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

Aget_data

Bfetch

Cread

Dprocess

Attempts:

3 left

💡 Hint

Common Mistakes

Using reserved keywords as function names

Using spaces or invalid characters in the name

The function name can be any valid identifier. Here, get_data is used as a clear name for an async function.

2fill in blank

medium

Complete the code to await an async database query call.

FastAPI

result = [1] db.fetch_one(query)

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

Ayield

Bawait

Casync

Dcall

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use await causing coroutine objects instead of results

Using async instead of await

In async functions, you use await to wait for async calls like database queries to complete.

3fill in blank

hard

Fix the error in the async function declaration for a FastAPI route.

FastAPI

@app.get("/items")
async def [1]():
    items = await db.fetch_all("SELECT * FROM items")
    return items

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

Afetch_items

Bitems

Cget_items

Ditems_list

Attempts:

3 left

💡 Hint

Common Mistakes

Using generic names like 'items' that can be confusing

Using names that don't match the route purpose

The function name get_items clearly indicates it handles a GET request for items, following common FastAPI naming conventions.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension filtering async query results.

FastAPI

filtered = {item['id']: item for item in results if item[1] [2] 10}

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

A["value"]

B>

C<

D['count']

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong keys that don't exist in items

Using wrong comparison operators

The comprehension filters items where the 'count' field is greater than 10, creating a dictionary keyed by 'id'.

5fill in blank

hard

Fill all three blanks to build an async function that queries and returns filtered data.

FastAPI

async def [1]():
    query = "SELECT * FROM users WHERE age [2] 21"
    results = await db.[3](query)
    return results

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

Aget_adult_users

B>

Cfetch_all

Dget_users

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong function names

Using incorrect SQL operators

Using sync methods instead of async

The function get_adult_users queries users older than 21 using fetch_all to get all matching records asynchronously.

Practice

1. What is the main benefit of using async database queries in FastAPI?

easy

A. It removes the need for database connections.

B. It makes the database run faster internally.

C. The app can handle other tasks while waiting for the database response.

D. It automatically caches all database results.

Solution

1. Step 1: Understand async behavior in FastAPI

   Async lets the app continue running other code instead of waiting for slow operations like database queries.

2. Step 2: Identify the benefit of async database queries

   This means the app stays responsive and can handle more requests while waiting for the database.

3. Final Answer:

   The app can handle other tasks while waiting for the database response. -> Option C

4. Quick Check:

   Async = non-blocking tasks [OK]

Hint: Async means do other work while waiting [OK]

Common Mistakes:

• Thinking async speeds up the database itself
• Believing async caches results automatically
• Assuming async removes database connections

2. Which of the following is the correct way to define an async function for a database query in FastAPI?

easy

A. async def get_data(): return await session.execute(query)

B. async def get_data(): return session.execute(query)

C. def get_data(): return await session.execute(query)

D. def get_data(): return session.execute(query)

Solution

1. Step 1: Recognize async function syntax

   Async functions must be declared with async def to use await inside.

2. Step 2: Match correct usage of await

   To wait for the database query, await must be used with the async session call.

3. Final Answer:

   async def get_data(): return await session.execute(query) -> Option A

4. Quick Check:

   Async function + await = correct syntax [OK]

Hint: Use async def with await inside async functions [OK]

Common Mistakes:

• Missing async keyword but using await
• Using await without async function
• Calling async functions without await

3. Given this async function in FastAPI using SQLAlchemy async session:

async def fetch_users(session):
    result = await session.execute("SELECT name FROM users")
    users = result.scalars().all()
    return users

What will fetch_users return?

medium

A. A coroutine object that needs awaiting

B. A list of user names from the database

C. A SQLAlchemy Result object

D. An error because scalars() is not async

Solution

1. Step 1: Understand await on session.execute

   The await waits for the query to finish and returns a Result object.

2. Step 2: Use scalars().all() on Result

   Calling scalars().all() extracts all values from the first column as a list.

3. Final Answer:

   A list of user names from the database -> Option B

4. Quick Check:

   await + scalars().all() = list output [OK]

Hint: await session.execute returns Result; scalars().all() gives list [OK]

Common Mistakes:

• Thinking fetch_users returns a coroutine, not awaited
• Expecting a Result object instead of list
• Assuming scalars() is async and causes error

4. Identify the error in this FastAPI async database query code:

async def get_items(session):
    result = session.execute("SELECT * FROM items")
    return await result.fetchall()

medium

A. Function should not be async

B. Cannot await fetchall() method

C. session.execute should not be async

D. Missing await before session.execute call

Solution

1. Step 1: Check usage of async session.execute

   session.execute is an async method and must be awaited to get the Result.

2. Step 2: Understand fetchall() usage

   fetchall() is called on the awaited Result; awaiting fetchall() is incorrect because it returns a list synchronously.

3. Final Answer:

   Missing await before session.execute call -> Option D

4. Quick Check:

   await session.execute needed before fetchall() [OK]

Hint: Always await async session.execute calls first [OK]

Common Mistakes:

• Not awaiting session.execute causing coroutine error
• Awaiting fetchall() which is not async
• Confusing async with sync methods

5. You want to fetch all active users asynchronously and return their emails in FastAPI. Which code snippet correctly uses async database queries and filters results?

hard

A. async def get_active_emails(session):
result = await session.execute("SELECT email FROM users WHERE active=1")
return result.scalars().all()

B. def get_active_emails(session):
result = session.execute("SELECT email FROM users WHERE active=1")
return result.scalars().all()

C. async def get_active_emails(session):
result = session.execute("SELECT email FROM users WHERE active=1")
return await result.scalars().all()

D. async def get_active_emails(session):
result = await session.execute("SELECT email FROM users")
return [email for email in result.scalars().all() if email.active == 1]

Solution

1. Step 1: Use async def and await session.execute

   The function must be async and await the async session.execute call with the correct SQL filter.

2. Step 2: Extract emails with scalars().all()

   Calling scalars().all() on the awaited result returns a list of emails matching the filter.

3. Final Answer:

   async def get_active_emails(session): result = await session.execute("SELECT email FROM users WHERE active=1") return result.scalars().all() -> Option A

4. Quick Check:

   Async + await + filtered query = correct [OK]

Hint: Await session.execute with filter, then scalars().all() [OK]

Common Mistakes:

• Using sync def with async calls
• Not awaiting session.execute
• Filtering results in Python instead of SQL