#!/usr/bin/perl
use strict;
# Buechereien -> german for Libraries
# Kundenkontakte -> german for customer-contacts
#
use Customercare::Buechereien;
use Customercare::Kundenkontakte;

my @kk = Customercare::Kundenkontakte->retrieve_all;

my $i = 0;
foreach (@kk) {
        last if $i++ > 10;
        printf "%02d. %s\n", $i, $_->customer->plzort;
        # This is where the problem occurs:
        foreach ( $_->kontakte ) {
                printf "  %s\n", $_->aktion_kurz;
        }
}

package Customercare::Buechereien;
use strict;
use base 'Customercare::DBI';

__PACKAGE__->set_up_table("buechereien");
__PACKAGE__->has_many(
        # This will create a new Method named "kontakte"
        "kontakte",
        'Customercare::Kundenkontakte' => "customer");

1;

package Customercare::Kundenkontakte;
use strict;
use base 'Customercare::DBI';

__PACKAGE__->set_up_table("kundenkontakte");
__PACKAGE__->has_a( customer => 'Customercare::Buechereien' );

1;


These are the tabledefinitions:

CREATE TABLE buechereien (
  customer varchar(50) NOT NULL default '',
  anschrift1 varchar(100) default NULL,
  plzort varchar(100) default NULL,
  tel varchar(50) default NULL,
  PRIMARY KEY  (customer)
) TYPE=MyISAM;

CREATE TABLE kundenkontakte (
  lfdnr int(11) NOT NULL auto_increment,
  customer varchar(50) NOT NULL default '',
  aktion_kurz varchar(50) NOT NULL default '',
  PRIMARY KEY  (lfdnr)
) TYPE=MyISAM;