my $rs = $schema->resultset('Topic')->search(undef);

foreach my $t ( $rs->all() ) {
	say "t: " . $t->topic();

	# geht	
	my $brs = $schema->resultset('Board')->search({topic_id => $t->topic_id()});
	say "board count: " . $brs->count();

	# geht nicht
	my $boards = $t->boards();
	say "board count: " . $boards->count();
}