has _industries  => ( is         => 'rw',
                      isa        => 'HashRef[Foo::Industry]',
                      auto_deref => 1,
                      default    => sub { {} },
                      clearer    => 'clear_industries',
                      traits     => ['Hash'],
                      handles    => { has_industry_id     => 'exists',
                                      add_industry        => 'set',
                                      get_industry_for_id => 'get',
                                      industry_ids        => 'keys',
                                      industries          => 'values',
                                      num_industries      => 'count',
                                    },
                    );