Here's the `database.py` file for your FastAPI backend named 'blog_app' with SQLite configuration using SQLAlchemy:

```python
# app/api/db/database.py

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

# SQLite database URL
SQLALCHEMY_DATABASE_URL = "sqlite:///./blog_app.db"

# Create the SQLAlchemy engine
engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)

# Create a SessionLocal class for database sessions
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

# Create a Base class for models
Base = declarative_base()
```

This file contains the following components:

1. **SQLALCHEMY_DATABASE_URL**: The URL for the SQLite database file `blog_app.db`.
2. **engine**: The SQLAlchemy engine created using the `create_engine` function with the `SQLALCHEMY_DATABASE_URL` and a specific connection argument for SQLite (`check_same_thread=False`).
3. **SessionLocal**: A class that creates database sessions using the `sessionmaker` function. The `autocommit` and `autoflush` parameters are set to `False` for better control over transactions.
4. **Base**: A base class for defining SQLAlchemy models, created using the `declarative_base` function.

You can import and use these components in your FastAPI application as follows:

```python
# Import the required components
from app.api.db.database import SessionLocal, engine, Base

# Create a database session
db = SessionLocal()

# Use the session for database operations
# ...

# Close the session
db.close()
```

Make sure to create the `app/api/db/` directory in your project structure before adding this file.