[FIXED] Displaying column in tableView

Issue

I'm trying to map and display data from tables between which there is a one-to-one relationship using TableView from JavaFX 8 and hibernate.

Tables:

@Entity
@Table(name = "CLUB")
public class Club implements Serializable {

    @Id
    @Column(name = "CLUB_ID", nullable = false, unique = true)
    private int clubId;

    @Column(name = "NAME", nullable = false, length = 100)
    private String name;

    @Column(name = "CITY", length = 50)
    private String city;

    @OneToOne(fetch = FetchType.LAZY, mappedBy = "club", cascade = CascadeType.ALL)
    private Trainer trainer;

    // constructor, getters, setters
}

and

@Entity
@Table(name = "TRAINER")
public class Trainer implements Serializable {

    @Id
    @Column(name = "LICENCE_NR", nullable = false, unique = true)
    private int licenceNr;

    @Column(name = "NAME", nullable = false, length = 50)
    private String name;

    @Column(name = "SURNAME", nullable = false, length = 50)
    private String surname;

    @OneToOne(fetch = FetchType.LAZY)
    @PrimaryKeyJoinColumn
    private Club club;

    // constructor, getters, setters
}

ClubController class with TableView:

public class ClubController implements Initializable {

    ...

    @FXML
    private TableView<Club> clubTableView;

    @FXML
    private TableColumn<Club, String> nameColumn;

    @FXML
    private TableColumn<Club, String> cityColumn;

    @FXML
    private TableColumn<Club, Integer> trainerColumn;

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        nameColumn.setCellValueFactory(new PropertyValueFactory<Club, String>("name"));
        cityColumn.setCellValueFactory(new PropertyValueFactory<Club, String>("city"));
        trainerColumn.setCellValueFactory(new Callback<TableColumn.CellDataFeatures<Club, Integer>, ObservableValue<Integer>>() {
            @Override
            public ObservableValue<Integer> call(TableColumn.CellDataFeatures<Club, Integer> param) {
                return new SimpleIntegerProperty(param.getValue().getTrainer().getLicenceNr()).asObject();
            }
        });
        clubTableView.setItems(getClub());
    }

    private ObservableList<Club> getClub() {
        ObservableList<Club> clubList = FXCollections.observableArrayList();
        Session session = HibernateUtil.config().openSession();
        List<Club> cList = session.createCriteria(Club.class).list();
        clubList.addAll(cList);
        session.close();
        return clubList;
    }

    ...
}

First two columns work correctly, but in the trainerColumn I have NPE. How to fix it?

Solution

The trainer field in the CLUB entity is lazy loaded:

...
    @OneToOne(fetch = FetchType.LAZY, mappedBy = "club", cascade = CascadeType.ALL)
    private Trainer trainer;
...

... which can only be read while the session that created the entity is opened.

In the ClubController, you opened and closed the session, without explicitly loading the trainer details from the DB:

    private ObservableList<Club> getClub() {
        ObservableList<Club> clubList = FXCollections.observableArrayList();

        // SESSION OPENED
        Session session = HibernateUtil.config().openSession();

        // CLUB ENTITIES LOADED WITH LAZY TRAINERS
        List<Club> cList = session.createCriteria(Club.class).list();
        clubList.addAll(cList);

        //SESSION CLOSED
        session.close();

        return clubList;
    }

So either make the trainer field in the CLUB entity to be eager loaded:

...
    @OneToOne(fetch = FetchType.EAGER, mappedBy = "club", cascade = CascadeType.ALL)
    private Trainer trainer;
...

Or explicitly load the trainer when querying the DB - with something as simple as:

...
        // SESSION OPENED
        Session session = HibernateUtil.config().openSession();

        // CLUB ENTITIES LOADED WITH LAZY TRAINERS
        List<Club> cList = session.createCriteria(Club.class).list();

        // EXPLICITLY LOAD ALL TRAINERS FROM DB
        cList.stream().peek(club -> club.getTrainer().getLicenceNr())
        clubList.addAll(cList);

        //SESSION CLOSED
        session.close();
...

Although, I advice against this last one, since is a bit dirty and less performing (many extra round trips to the DB, instead of a single join query for all one-to-one record query if eager); but still available.

Answered By - Marco R.