14 - One To Many Mapping

A one-to-many relationship occurs when one entity is related to many occurrences in another entity.

UserDetails.java

package org.yash.dto;

import java.util.ArrayList;

import java.util.Collection;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.OneToMany;

import javax.persistence.Table;

@Entity

@Table(name="USER_DETAILS")

public class UserDetails {

      /* @Id says "userId" is primary key */

      @Id @GeneratedValue (strategy=GenerationType.AUTO)

      private int userId;    

      private String userName;

      @OneToMany(mappedBy="user")

      private Collection<Vehicle> vehicle = new ArrayList<Vehicle>();

           

      public int getUserId() {

            return userId;

      }

      public void setUserId(int userId) {

            this.userId = userId;

      }

      public String getUserName() {

            return userName;

      }

      public void setUserName(String userName) {

            this.userName = userName;

      }

      public void setVehicle(Collection<Vehicle> vehicle) {

            this.vehicle = vehicle;

      }

      public Collection<Vehicle> getVehicle() {

            return vehicle;

      }

}

HibernateTest.java

package org.yash.hibernate;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.yash.dto.UserDetails;

import org.yash.dto.Vehicle;

public class HibernateTest {

      public static void main(String args[]){

            UserDetails user = new UserDetails();

            user.setUserName("First User");

           

            Vehicle vehicle = new Vehicle();

            vehicle.setVehicleName("Car");

           

            Vehicle vehicle2 = new Vehicle();

            vehicle2.setVehicleName("Jeep");

           

            user.getVehicle().add(vehicle);

            user.getVehicle().add(vehicle2);

           

            vehicle.setUser(user);

            vehicle2.setUser(user);

           

            SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();         

            Session session = sessionFactory.openSession();

            /* It is used to save all the objects and to define single unit of work */

            session.beginTransaction();

           

            session.save(user);

            session.save(vehicle);

            session.save(vehicle2);

           

            session.getTransaction().commit();

            session.close();

      }

}

Vehicle.java

package org.yash.dto;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

@Entity

public class Vehicle {

      @Id @GeneratedValue

      private int vehicleId;

      private String vehicleName;

      @ManyToOne

      @JoinColumn(name="user_id")

      private UserDetails user;

      public int getVehicleId() {

            return vehicleId;

      }

      public void setVehicleId(int vehicleId) {

            this.vehicleId = vehicleId;

      }

      public String getVehicleName() {

            return vehicleName;

      }

      public void setVehicleName(String vehicleName) {

            this.vehicleName = vehicleName;

      }

      public void setUser(UserDetails user) {

            this.user = user;

      }

      public UserDetails getUser() {

            return user;

      }

}

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <property name="connection.driver_class">

            org.postgresql.Driver

        </property>

        <property name="connection.url">

            jdbc:postgresql://localhost:5433/hibernatedb

        </property>

        <property name="connection.username">postgres</property>

        <property name="connection.password">admin</property>

        <!-- JDBC connection pool (use the built-in) -->

        <property name="connection.pool_size">1</property>

        <!-- SQL dialect -->

        <property name="dialect">

            org.hibernate.dialect.PostgreSQLDialect

        </property>

        <!-- Enable Hibernate's automatic session context management -->

        <property name="current_session_context_class">thread</property>

       

        <!-- Echo all executed SQL to stdout -->

        <property name="show_sql">true</property>

       

        <!-- Drop and re-create the database schema on startup -->

            <property name="hbm2ddl.auto">create</property> 

<!-- create / update -->

   

          <!-- Names the annotated entity class -->

            <mapping class="org.yash.dto.UserDetails"/>    

            <mapping class="org.yash.dto.Vehicle"/>  

           

    </session-factory>

</hibernate-configuration>