Check out the section on the has_many and has_a methods. You will want to add something like the following to your classes:

# To your authors class
__PACKAGE__->has_many('books', 'My::DB::Books' => book_id);

# To your books class
__PACKAGE__->has_a('author_id', 'My::DB::Authors');
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Then in your code you can use:

my $author = My::DB::Authors->retrieve($author_id);

# method add_to_books is created for you by has_many
$author->add_to_books({
                       col1 => value1,
                       col2 => value2,
                       ...
});  # author_id will be filled in automatically

my $books = $author->books;
while (my $book = $books->next) {
  ...
}
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- Cees