package Foo::Exceptions;
use strict;
use warnings;

use Exception::Class (

	'Foo::Exception::DBI' => {
		description => 'DBI Error',
		# error => $DBI::errstr,
	},

	'Foo::Exception::DBI::Dupe' => {
		description => 'Duplicate key',
		isa => 'Foo::Exception::DBI',
		# error => name of duplicate key,
	},
	
	'Foo::Exception::Dupe' => {
		description => 'Duplicate entry',
		fields => [ 'name' ],
		# error => value of duplicate field
	},

        # etc.

);

##</code><code>##

Foo::Exception::DBI->throw($DBI::errstr)
Foo::Exception::Dupe->throw(name => $name, error => $value);

##</code><code>##

eval {$foo->something_that_might_die};
if (ref($@)) {
    if ($@->isa('Foo::Exception::Dupe') ) {
        warn "duplicate entry ", $@->name, " ($@)\n"; undef $@;
    };
};
die $@ if $@;