Hibernate relationship issues - database

Question

I'm trying to store a couple of objects in a Oracle database using Hibernate. However, I can't seem to get the mapping relations right. As it stands I'm getting a NullPointerException.
In the end, every Client should contain an id, a first and last name, an e-mail and a set of reservations.
Every flight should contain a flight number, a starting time and a starting airport.
The bookings should have an id, client, flight, the date of booking and the amount of booked seats.
At the moment I'm just testing it with a single client as to not over-complicate it but I have gotten rather confused.
Here is what I have done till now:
Main
import java.sql.Date;
import java.sql.Time;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class JPAApplication {
private EntityManagerFactory entityManagerFactory;
public JPAApplication() {
Logger.getLogger("org.hibernate").setLevel(Level.ALL);
entityManagerFactory = Persistence.createEntityManagerFactory("DB1");
}
public void testFlights() {
EntityManager em = entityManagerFactory.createEntityManager();
em.getTransaction().begin();
Client firstClient = new Client("Kiro", "Betona", "kirobetona#gmail.com");
em.persist(firstClient);
}
public static void main(String[] args) {
JPAApplication app = new JPAApplication();
app.testFlights();
}
}
Client
import java.util.*;
import javax.persistence.*;
import javax.validation.constraints.NotNull;
#Entity
public class Client {
private int id;
private String firstName;
private String lastName;
private String email;
private Set<Booking> reservations;
Client(String firstName, String lastName, String email) {
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
}
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
public int getId() {
return id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public void setId(int id) {
this.id = id;
}
#OneToMany(targetEntity = Booking.class, mappedBy="client", fetch=FetchType.EAGER)
public Set<Booking> getReservations() {
return reservations;
}
public void setReservations(Set<Booking> reservations) {
this.reservations = reservations;
}
}
Booking
import java.util.Date;
import javax.persistence.*;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.validation.constraints.NotNull;
#Entity
public class Booking {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
private Client client;
private Flight flight;
private int bookedSeats = 1;
#Temporal(TemporalType.DATE)
private Date bookingDate;
Booking(Client client, Flight flight, Date bookingDate) {
this.client = client;
this.flight = flight;
this.bookingDate = bookingDate;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
#ManyToOne
#JoinColumn(name="id")
public Client getClient() {
return client;
}
#OneToOne
#PrimaryKeyJoinColumn(name="flight")
public Flight getFlight() {
return flight;
}
public int getBookedSeats() {
return bookedSeats;
}
public void setBookedSeats(int bookedSeats) {
this.bookedSeats = bookedSeats;
}
public Date getBookingDate() {
return bookingDate;
}
public void setBookingDate(Date bookingDate) {
this.bookingDate = bookingDate;
}
public void setClient(Client client) {
this.client = client;
}
public void setFlight(Flight flight) {
this.flight = flight;
}
}
Flight
import java.sql.Time;
import javax.persistence.*;
import javax.validation.constraints.NotNull;
#Entity
public class Flight {
private String flightNumber;
private Time startingTime;
private String startingAirport;
Flight(String flightNumber, Time startingTime, String startingAirport) {
this.flightNumber = flightNumber;
this.startingTime = startingTime;
this.startingAirport = startingAirport;
}
#Id
#OneToOne(targetEntity = Booking.class, mappedBy="flight", fetch=FetchType.EAGER)
#PrimaryKeyJoinColumn(name="flight")
public String getFlightNumber() {
return flightNumber;
}
public Time getStartingTime() {
return startingTime;
}
public void setStartingTime(Time startingTime) {
this.startingTime = startingTime;
}
public String getStartingAirport() {
return startingAirport;
}
public void setStartingAirport(String startingAirport) {
this.startingAirport = startingAirport;
}
public void setFlightNumber(String flightNumber) {
this.flightNumber = flightNumber;
}
}

Answer 1

I see some confusion when you are using the #JoinColumn annotation in Booking: you are telling Booking to use a column named "id" as the Foreign Key to Client, however that conflicts with the Booking primary key.
You could instead make the column name separate, like this:
#JoinColumn(name="clientId")
Also, for Hibernate to instantiate the Entity objects, the entity should have a no-arg constructor. The default no-arg constructors have been overridden in the example code.