from pydantic import BaseModel, Field
from uuid import UUID

# Base schema for Book
class BookBase(BaseModel):
    title: str = Field(..., description="Book title")
    author: str = Field(..., description="Author name")
    description: str | None = Field(None, description="Book description")
    author_id: UUID = Field(..., description="Author ID")

    class Config:
        schema_extra = {
            "example": {
                "title": "The Great Gatsby",
                "author": "F. Scott Fitzgerald",
                "description": "A classic American novel about the Roaring Twenties.",
                "author_id": "a7d93b0e-8c6d-4d1a-9e9c-b0e9d8c8d9f3"
            }
        }

# Schema for creating a new Book
class BookCreate(BookBase):
    pass

# Schema for Book responses
class Book(BookBase):
    id: UUID = Field(..., description="Book ID")

    class Config:
        orm_mode = True
```

This code defines three Pydantic schemas for the Book entity:

1. `BookBase`: A base schema that includes the common fields for the Book entity.
2. `BookCreate`: A schema that inherits from `BookBase` and is used for creating a new Book (e.g., in a POST request).
3. `Book`: A schema that inherits from `BookBase` and includes an additional `id` field, which is typically used for API responses.

The `Field` class is used to add validation and metadata to the fields. For example, the `title` and `author` fields are required, while the `description` field is optional. The `author_id` field is a UUID, and the `id` field in the `Book` schema is also a UUID.

The `Config` class is used to provide additional configuration options, such as including example values for the fields.

Note that this code assumes that you have installed the `pydantic` library and imported the necessary modules (`BaseModel`, `Field`, and `UUID`).