Hi, I'm a noobie, and this is a simple question. If it has already
been answered a thousand times prior, please just tell me the link 
A book can have many authors...an author can write many books:
I have a simple model Books:
create table books ( id int not null auto_increment, isbn varchar(25) not null, <etc.......other columns here> primary key (id) );
class Book < ActiveRecord::Base has_and_belongs_to_many :authors
<etc....>
A simple model Authors:
create table authors ( id int not null auto_increment, first_name varchar(25) not null, last_name varchar(25) not null, primary key (id) );
A simple join table for many-to-many:
create table authors_books ( book_id int not null, author_id int not null, constraint fk_ab_book foreign key (book_id) references books(id), constraint fk_ab_author foreign key (author_id) references authors(id) ) ;
class Author < ActiveRecord::Base has_and_belongs_to_many :books
<etc.....>
Here's my question:
When I create a new book, I need to compile the list of authors and save them so they'll be linked with the book via the authors_books table. If the author already exists, I want to re-use that author in the db, and not create a new author.
Pseudo-code like this (not ruby):
book = Book.new( ...all book params here)
foreach author a: if author already exists in db authors.add(a) else author = Author.new(first_name, last_name) authors.add(author) end
book.authors = authors
book.save