retrieve data of collection type from database using getters and setters

Question

i am having three classes one is USER, second Vehicle and third is notfound_test.
In USER class i declared vehicle as Collection as follow.
Collection vehicle=new ArrayList();
And also having getters and setters of it.
So, my question is how i can retrieve data from database i am using hibernate?
I tried following code.
i am unable from getting data in JOPTIONPANE OF VEHICLE IN THIRD CLASS.i wanted the associated data

package org.notfound.annotation;

import java.util.ArrayList;
import java.util.Collection;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class User {

@Id @GeneratedValue
private int id;
private String name;
@OneToMany
Collection<Vehicle> vehicle=new ArrayList<Vehicle>();


public Collection<Vehicle> getVehicle() {
    return vehicle;
}
public void setVehicle(Collection<Vehicle> vehicle) {
    this.vehicle = vehicle;
}
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}


}

package org.notfound.annotation;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Vehicle {

@Id @GeneratedValue
private int vehicle_id;
private String vehicle_name;
@ManyToOne
private User user=new User();



public User getUser() {
    return user;
}
public void setUser(User user) {
    this.user = user;
}
public int getVehicle_id() {
    return vehicle_id;
}
public void setVehicle_id(int vehicle_id) {
    this.vehicle_id = vehicle_id;
}
public String getVehicle_name() {
    return vehicle_name;
}
public void setVehicle_name(String vehicle_name) {
    this.vehicle_name = vehicle_name;
}


}

 package org.notfound.annotation;

 import javax.swing.JOptionPane;

 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Configuration;

 public class Notfound_test {


public static void main(String[] args) {

    User user=new User();
    Vehicle vehicle=new Vehicle();
    Vehicle vehicle2=new Vehicle();

    user.setName("NIRAV J. KAMANI");
    vehicle.setVehicle_name("CHEVROLET CRUIZE");
    vehicle2.setVehicle_name("MARUTI ERTIGA");
    vehicle.setUser(user);
    vehicle2.setUser(user);
    user.getVehicle().add(vehicle);
    user.getVehicle().add(vehicle2);

    SessionFactory sessionfactory=new Configuration().configure().buildSessionFactory();
    Session session=sessionfactory.openSession();
    /*session.beginTransaction();
    session.save(user);
    session.save(vehicle);
    session.save(vehicle2);
    session.getTransaction().commit();
    session.close();*/

    session.beginTransaction();
    user=(User) session.get(User.class, 1);
    vehicle=(Vehicle) session.get(Vehicle.class, 1);
    vehicle2=(Vehicle) session.get(Vehicle.class, 2);
    JOptionPane.showMessageDialog(null, user.getId()+" "+user.getName()+" "+user.getVehicle().toString(), "INFORMATION", JOptionPane.INFORMATION_MESSAGE);
    session.close();

}

}

Answer 1

As always, you forgot the mappedBy annotation on the OneToMany. It's a bidirectional OneToMany association, and the one side must thus be the inverse side of the many side, as explained in the documentation :

@OneToMany(mappedBy = "user")
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();

I also renamed the fields to vehicles , since it's a collection, and thus contains several ones.

EDIT:

Your comment shows that the 2 vehicles are printed:

[org.notfound.annotation.Vehicle@37ed25, org.notfound.annotation.Vehicle@aec63]
 ^-- first vehicle                       ^-- second vehicle
^-- brackets, indicating that it's a collection ------------------------------^

If you want them to be printed is a different way than the dafult way, you need to override the toString() method in vehicle, as for any Java object.