[SQLObject] How do I update a many-to-many field?

[Mike K. <mrm...@co...>]

Given the following simple schema:

class Author(SQLObject):
    lastName = StringCol(length=40, notNone=True)
    books = RelatedJoin('Book')  # An author can write many books

class Book(SQLObject):
    title = StringCol(length=100, notNone=True)
    authors = RelatedJoin('Author')  # A book can have many authors

I then make an Author and a Book:

author = Author("Seuss")
book = Book("The Cat In The Hat")

Now I want to give the book an author:

book.addAuthor(author)

Hmm, let's make a new author and change the book's author:

author = Author("Geissel")
book.addAuthor(author)

No, that's not right.  I just gave that book two authors.

What I want is some kind of update that will properly handle the deletion of the
previous author and addition of the new author to the magic book-to-author table
SQLObject created for me.  Or at least a way for me to delete the previous
author entries for this book, so I can add the new author entries.  So what's
the correct way to handle this type of CRUD?