Other DB interfaces, such as Class::DBI, Class::Tables, or DBIx::Recordset, do not quite feel right to me, in case you were wondering.

The schema here has three tables: person, has_book, and book. The person table holds people and the book table holds books and the has_book table holds pointers to a person and a book. You'll note that the code does not mention the has_book table at all -- that is because the path from person to book through has_book is inferred from the schema.

use strict;
use DBI;
use SetDB;

# Must turn off no strict subs so I can use magical barewords
# This is certainly not required for using this module
no strict 'subs';

# Okay, first we set up our DBI connection
my $dbi = DBI->connect('DBI:mysql:database=setdb_test;host=localhost',
  'setdb', 'setdb');

# Now we set up our schema (see website for the file)
use vars qw( $schema );
do 'schema.pl';

# This creates our SetDB database
my $db = new SetDB($dbi, $schema);

# Lets get a set of people and their books
my $people = $db->newSet(person, [book]);

# Now loop through and print out each person
while(my $person = $people->fetchNext())
{
  print "Name: $person->{name}\n";

  # This is the set of books which that person has
  my $books = $person->{book};

  # Lets go ahead and print all of their books
  while(my $book = $books->fetchNext())
  {
    print "  Book: $book->{title}\n";

    # Demonstrate updates by adding ' sucks!' to the book's title
    $book->{title} .= ' sucks!';
  }
}
[download]

This looks like the following when run (two executions to demonstrate the database update -- oh, and Joe has no books, BTW):

awwaiid@feline:~/projects/perl/setdb$ ./setdb_demo.pl
Name: Bob
  Book: How to Take Over the World!
  Book: When I Went Shopping
Name: Joe
Name: Frank
  Book: How to Take Over the World! sucks!
  Book: How to build a turtle
  Book: Turtle Soup

awwaiid@feline:~/projects/perl/setdb$ ./setdb_demo.pl
Name: Bob
  Book: How to Take Over the World! sucks! sucks!
  Book: When I Went Shopping sucks!
Name: Joe
Name: Frank
  Book: How to Take Over the World! sucks! sucks! sucks!
  Book: How to build a turtle sucks!
  Book: Turtle Soup sucks!
[download]

The code to make this happen includes such strange things as an object who's blessed thingie is a tied hash back to itself so that it can detect changes to its own hash elements... something which would not work out so well (or not be quite so possible) in just about any other language I can think of, thats for sure!

So what do you think? Cool Use for Perl? There is a lot to be done here and a lot more ideas for this project which I will eventually implement. Please tell me your ideas!

See http://thelackthereof.org/wiki.pl/SetDB for full code and eventual updates.

UPDATE: Fixed some code a bit.