best method to save-through to many-to-many

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 :slight_smile:

A book can have many 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


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
) ;

class Author < ActiveRecord::Base
  has_and_belongs_to_many :books


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 = ...all book params here)

foreach author a:
  if author already exists in db
    author =, last_name)

book.authors = authors