Convert List of Objects to List of Strings - string

Question

I'm using Spring data jpa findAll() method. So it returns List of objects.
here is the entity.
#Entity
#Table(name = "country")
#Data
public class CountryEntity {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "country_id")
private Long id;
#Column(name = "country_name")
private String name;
#OneToMany(mappedBy ="countryEntity")
private Collection<GovernmentEntity> governments;
}
and data jpa findAll() method is
List<CountryEntity> entities = countryRepo.findAll();
I want to get list of Country names as String WITHOUT USING loops or streams (performance issues).
I used streams and it works fine with javaFx ListView
#FxmlView("/address.fxml")
#Component
#RequiredArgsConstructor
public class HomeController implements Initializable {
private ObservableList<String> countriesNames;
#FXML
private ListView<String> countryListView;
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
List<CountryEntity> entities = countryRepo.findAll();
List <String> countryList = entities.stream().map(o-> Objects.toString(o.getName())).collect(Collectors.toList());
countriesNames = FXCollections.observableList(countryList);
countryListView.getItems().addAll(countriesNames);
}
}

Answer 1

Make your ListView a ListView<CountryEntity>, and use a cell factory to customize the display:
public class HomeController implements Initializable {
private ObservableList<String> countriesNames;
#FXML
private ListView<CountryEntity> countryListView;
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
List<CountryEntity> entities = countryRepo.findAll();
countryListView.getItems().addAll(entities);
countryListView.setCellFactory(lv -> new ListCell<CountryEntity>() {
#Override
protected void updateItem(CountryEntity country, boolean empty) {
super.updateItem(country, empty);
if (empty || country == null) {
setText("");
} else {
setText(country.getName()); // or however you want to display it
}
});
}
}
If you genuinely only want a list of country names, and don't want to retrieve a list of CountryEntitys and extract the names from them, then you need to define a method in your repository for the purpose:
public interface CountryEntityRepository extends JpaRepository<CountryEntity, Long> {
// existing methods...
#Query("select c.name from CountryEntity c")
List<String> findCountryNames() ;
}
And then of course just do
#FXML
private ListView<String> countryListView ;
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
countryListView.getItems().addAll(countryRepo.findCountryNames());
}
However, the first approach is almost certainly preferred. You will likely need the other data in the CountryEntity at some point.