Here's the `database.py` file for the `blog_app` FastAPI backend, configured with SQLite using SQLAlchemy:


from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URL = "sqlite:///./blog_app.db"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}

SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

Base = declarative_base()

def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

Explanation:

1. We import the necessary modules from SQLAlchemy: `create_engine`, `declarative_base`, and `sessionmaker`.
2. We define the SQLite database URL using `SQLALCHEMY_DATABASE_URL = "sqlite:///./blog_app.db"`. This will create a new SQLite database file named `blog_app.db` in the current directory if it doesn't exist, or use the existing one if it does.
3. We create the SQLAlchemy engine using `create_engine(SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False})`. The `connect_args` parameter is required for SQLite to avoid threading issues.
5. We create a `Base` class using `declarative_base()`. This class will be used as the base class for defining database models.