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@OneToMany in Hibernate Annotation

By Arvind Rai, February 06, 2013
@OneToMany in hibernate annotation is used for mapping two tables. @OneToMany associates a parent table and one child table in the way that a parent can have more than one child. @JoinColumn joins the parent table and child table by a column. We have two entities Country and State. We are mapping these two tables. Here Country is parent and State is child. One country can have more than states.
Country.java
package com.concretepage.persistence;

import java.io.Serializable;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;

@Entity
public class Country implements Serializable {
	private static final long serialVersionUID = 1L;
	@Id
	@Column(name="id")
	private int id;
	
	@Column(name="name")
	private String name;
	
	@OneToMany(cascade=CascadeType.ALL)
	@JoinColumn(name="country_id")
	private Set<State> states;
	
	public Country(int id,String name,Set<State> states){
		this.id=id;
		this.name=name;
		this.states=states;
	}
	public Country(){
	}
	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;
	}
	public Set<State> getStates() {
		return states;
	}
	public void setStates(Set<State> states) {
		this.states = states;
	}
}
 



State.java
package com.concretepage.persistence;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "state")
public class State {
	@Id
	@Column(name = "id")
	private int id;

	@Column(name = "name")
	private String name;
		
	public State(int id,String name){
		this.id=id;
		this.name=name;
	}
	public State(){}
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}
	
}
 
hibernate.cfg.xml
<!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="hibernate.connection.url">
    jdbc:mysql://localhost:3306/hibernate</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password"></property>
    <property name="hibernate.connection.pool_size">10</property>
    <property name="show_sql">true</property>
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.hbm2ddl.auto">update</property>
    <property name="hibernate.cache.use_second_level_cache">true</property>
    <mapping class="com.concretepage.persistence.State"/>
    <mapping class="com.concretepage.persistence.Country"/>
   </session-factory>
</hibernate-configuration>
 
HibernateUtil.java
package com.concretepage.util;
import java.util.HashSet;
import java.util.Set;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

import com.concretepage.persistence.Country;
import com.concretepage.persistence.State;

public class HibernateUtil {
	private static final SessionFactory concreteSessionFactory;
	    static {
	        try {
	            concreteSessionFactory = new AnnotationConfiguration()
	                    .configure().buildSessionFactory();
	        } catch (Throwable ex) {
	            throw new ExceptionInInitializerError(ex);
	        }
	    }
	    public static Session getSession()
	            throws HibernateException {
	        return concreteSessionFactory.openSession();
	    }
	    
	    public static void main(String... args){
	    	Session session=getSession();
	    	session.beginTransaction();
	    	State s1= new State(1,"UP");
	    	State s2= new State(2,"MP");
	    	Set<State> states= new HashSet<State>();
	    	states.add(s1);
	    	states.add(s2);
	    	Country country= new Country(1,"India",states);
	    	session.persist(country);
	    	session.getTransaction().commit();
	    	session.close();
	    }
	}
 
Output
Hibernate: insert into Country (name, id) values (?, ?)
Hibernate: insert into state (name, id) values (?, ?)
Hibernate: insert into state (name, id) values (?, ?)
Hibernate: update state set country_id=? where id=?
Hibernate: update state set country_id=? where id=?
 
POSTED BY
ARVIND RAI
ARVIND RAI
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