Async Database Connections in FastAPI: Best Practices and Key Considerations with async/await

FastAPI, a modern web framework for Python, natively supports asynchronous processing using async/await, making it an excellent choice for building fast and scalable web applications.

Among all features, introducing asynchronous processing for database connections is crucial for overall performance and responsiveness. However, for developers used to traditional synchronous DB connections, adopting async/await can involve a learning curve and several important considerations.

In this article, we’ll walk through the advantages and disadvantages of async DB connections in FastAPI, introduce popular async-compatible ORMs, and highlight important tips for developers transitioning from synchronous programming, along with practical code examples.

1. Why Is FastAPI So Good at Asynchronous Processing?

FastAPI is built on Python’s asyncio framework and uses an architecture that doesn’t consume a thread for each request. This allows it to achieve high concurrency and responsiveness.

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def read_root():
    return {"message": "Hello, world!"}

By defining routes with async def, requests can be handled asynchronously.

2. Benefits of Asynchronous DB Connections

✅ High Throughput and Efficient Resource Usage

Async DB clients don’t block during DB response time, allowing other requests to be processed. This makes better use of resources under high concurrency.

✅ Faster Response Time

Async handling of external APIs and DBs reduces overall latency. This is especially effective in I/O-bound scenarios.

✅ Strong Compatibility with Python Ecosystem

An increasing number of async-compatible ORMs and drivers make asynchronous programming more viable in Python projects.

3. Async-Compatible DB Clients and ORMs

To use async DB connections in FastAPI, consider the following libraries:

4. Async DB Connection Example with Databases

Install Dependencies

pip install databases[sqlite] sqlalchemy

Code Example

from fastapi import FastAPI
import databases
import sqlalchemy

DATABASE_URL = "sqlite+aiosqlite:///./test.db"

database = databases.Database(DATABASE_URL)
metadata = sqlalchemy.MetaData()
app = FastAPI()

@app.on_event("startup")
async def startup():
    await database.connect()

@app.on_event("shutdown")
async def shutdown():
    await database.disconnect()

@app.get("/users")
async def get_users():
    query = "SELECT * FROM users"
    return await database.fetch_all(query)

Here, await database.connect() ensures the DB connection is handled asynchronously.

5. Key Tips for Developers Used to Synchronous Processing

❗ Avoid Mixing with Synchronous Libraries

Using synchronous tools like sqlalchemy.orm.Session inside async def can cause blocking I/O, negating the benefits of async. Use async-compatible versions like async_session.

❗ Don’t Forget await

Always use await with async functions. Forgetting it will return an unresolved object like a Promise, leading to unexpected bugs.

❗ Manage Connection Pools Carefully

Async processing can obscure connection limits, and high concurrent access might degrade performance or crash the DB. Tune your pool settings appropriately.

6. Drawbacks and Challenges of Async DB Connections

🔸 Steeper Learning Curve

For beginners, the async/await syntax and library usage may feel unfamiliar at first.

🔸 Library Support Varies

Some ORMs and tools (e.g., Django ORM) don’t fully support async, so workarounds or limitations may apply.

🔸 Debugging Is More Complex

Async code can make error handling and stack traces harder to interpret. Robust logging and monitoring are essential.

7. Conclusion: Async DB Connections Unlock FastAPI’s True Power

FastAPI shines with asynchronous processing. By leveraging async DB connections, you can build scalable and high-performance Web APIs—but this also requires careful design, the right libraries, and attention to async-specific details.

✅ Async DB Connection Best Practices:

• Use async def and await correctly
• Choose async-compatible ORMs and clients
• Avoid blocking I/O operations
• Manage connections and handle errors with care

At first, async programming might feel complex—but once you get the hang of it, FastAPI with async DBs will become your ultimate development duo!