How to implement database connection and transaction processing in FastAPI

How to implement database connection and transaction processing in FastAPI

Introduction:
With the rapid development of Web applications, database connection and transaction processing have become a very important topic. FastAPI is a high-performance Python web framework loved by developers for its speed and ease of use. In this article, we will introduce how to implement database connections and transactions in FastAPI to help you build reliable and efficient web applications.

Part One: Database Connection
In FastAPI, various database connection tools can be used, such as SQLAlchemy and Tortoise-ORM. We will use SQLAlchemy as an example to demonstrate.

1. Install SQLAlchemy and MySQL driver
   First, we need to install the SQLAlchemy library and the corresponding MySQL driver. You can install it using the following command:

pip install sqlalchemy
pip install mysql-connector-python

2. Create database connection
   In FastAPI application, we can create database connection in the main application and inject it into route processing in process. The following is a sample code:

from fastapi import Depends, FastAPI
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm.session import Session

app = FastAPI()

SQLALCHEMY_DATABASE_URL = "mysql+mysqlconnector://user:password@localhost/db_name"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL,
    pool_size=10,
    max_overflow=20
)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
Base = declarative_base()

async def get_db() -> Session:
    try:
        db = SessionLocal()
        yield db
    finally:
        db.close()

In the above code, we first create the URL of the database connection, and then use SQLAlchemy's create_engine function to create the database engine. Next, we define a SessionLocal class for maintaining database sessions. Finally, we create a dependency function get_db that will return a database session instance for use in each request handler.

Part 2: Transaction Processing
In FastAPI, transaction processing can be used to ensure the atomicity and consistency of database operations. Below is some sample code that demonstrates how to use transactions with FastAPI.

1. Injecting the database session using dependencies
   We will continue to use the get_db dependency function created earlier in this example and inject the database session in the route handler.

from fastapi import Depends, FastAPI
from sqlalchemy.orm import Session
from .models import User
from .crud import create_user
from .database import get_db

app = FastAPI()

@app.post("/users/")
async def create_user_handler(user: User, db: Session = Depends(get_db)):
    return create_user(db=db, user=user)

In the above code, we define a route handler create_user_handler that accepts a user object and database session as parameters. In this handler, we call a function called create_user which will create a new user in the database.

2. Implementing Transaction Processing
   The following is the code for an example create_user function, which demonstrates how to use transaction processing in a database session:

from sqlalchemy.orm import Session
from .models import User

def create_user(db: Session, user: User):
    try:
        db.begin()
        db.add(user)
        db.commit()
        db.refresh(user)
        return user
    except:
        db.rollback()
        raise

In the above code , we first use the db.begin() statement to start a transaction. We then add the user object to the database session using the db.add() statement. Next, we commit the transaction to the database using the db.commit() statement. If an error occurs during the commit process, we use the db.rollback() statement to roll back the transaction. Finally, we refresh the user object using the db.refresh() statement to ensure that it contains the primary key value generated in the database.

Conclusion:
In this article, we introduced how to implement database connection and transaction processing in FastAPI. We first created the database connection using SQLAlchemy and then used the dependency function to inject the database session into the route handler. Next, we demonstrated how to use transactions within a database session to guarantee atomicity and consistency of database operations. By learning and practicing these techniques, you will be able to build reliable and efficient web applications.

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