Sure, here's an example of a FastAPI endpoint that saves a book to the database using SQLAlchemy and Pydantic:

```python
from typing import List
from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from sqlalchemy import Column, Integer, String, create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

from app.api.models.books_model import *
from app.api.schemas.books_schema import *
# Create the database engine and session
engine = create_engine('sqlite:///books.db', echo=True)
Session = sessionmaker(bind=engine)
session = Session()

# Define the base class for SQLAlchemy models
Base = declarative_base()

# Define the Book model

    class Config:
        orm_mode = True

# Define the FastAPI app
app = FastAPI()

# Define the POST endpoint to save a book
@app.post('/books', response_model=BookSchema)
def create_book(book: BookSchema):
    # Create a new Book instance from the Pydantic schema
    new_book = Book(title=book.title, author=book.author, description=book.description)

    # Add the new book to the database session
    session.add(new_book)
    session.commit()

    return new_book

# Run the FastAPI app
if __name__ == '__main__':
    import uvicorn
    uvicorn.run(app, host='0.0.0.0', port=8000)
```

Here's how it works:

1. We define the `Book` model using SQLAlchemy, which maps to the `books` table in the database.
2. We create a Pydantic `BookSchema` that defines the expected input data for a book.
3. We define a `POST` endpoint at `/books` using FastAPI, which accepts a `BookSchema` instance as input.
4. Inside the endpoint function, we create a new `Book` instance from the Pydantic schema data.
5. We add the new `Book` instance to the database session and commit the changes.
6. We return the newly created `Book` instance as the response.

To test the endpoint, you can use a tool like `curl` or a REST client like Postman. Here's an example using `curl`:

```
curl -X POST -H "Content-Type: application/json" -d '{"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "description": "A classic novel about the Jazz Age."}' http://localhost:8000/books
```

This will create a new book in the `books.db` SQLite database file.