Hibernate Many to Many Example using XML

We can map many to many relation either using list, set, bag, map, etc. Here, we are going to use list for many-to-many mapping. In such case, three tables will be created.

Example of Many to Many Mapping

In this example, we will generate a many to many relation between questions and answers using list.

1) Create the Persistent class

There are two persistent classes Question.java and Answer.java. Question class contains Answer class reference and vice versa.

Question.java

package com.javatpoint;  
  
import java.util.List;  
  
public class Question {  
private int id;  
private String qname;  
private List<Answer> answers;

public int getId() {
	return id;
}
public void setId(int id) {
	this.id = id;
}
public String getQname() {
	return qname;
}
public void setQname(String qname) {
	this.qname = qname;
}
public List<Answer> getAnswers() {
	return answers;
}
public void setAnswers(List<Answer> answers) {
	this.answers = answers;
}    
}

Answer.java

package com.javatpoint;

import java.util.*;

public class Answer {  
private int id;  
private String answername;  
private String postedBy;  
private List<Question> questions;
public int getId() {
	return id;
}
public void setId(int id) {
	this.id = id;
}
public String getAnswername() {
	return answername;
}
public void setAnswername(String answername) {
	this.answername = answername;
}
public String getPostedBy() {
	return postedBy;
}
public void setPostedBy(String postedBy) {
	this.postedBy = postedBy;
}
public List<Question> getQuestions() {
	return questions;
}
public void setQuestions(List<Question> questions) {
	this.questions = questions;
}  
}

2) Create the Mapping file for the persistent class

Here, we have created the question.hbm.xml and answer.hbm.xml file for defining the list.

question.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-mapping PUBLIC  
          "-//Hibernate/Hibernate Mapping DTD 5.3//EN"  
          "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd">  
            
<hibernate-mapping>  

  <class name="com.javatpoint.Question" table="ques1911">
		<id name="id" type="int">
			<column name="q_id" />
			<generator class="increment" />
		</id>
		<property name="qname" />

		<list name="answers" table="ques_ans1911" fetch="select" cascade="all">
			<key column="q_id" />
			   <index column="type"></index> 
			<many-to-many class="com.javatpoint.Answer" column="ans_id" />
		</list>
	</class> 
</hibernate-mapping>       

answer.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-mapping PUBLIC  
          "-//Hibernate/Hibernate Mapping DTD 5.3//EN"  
          "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd">  
            
<hibernate-mapping>  
<class name="com.javatpoint.Answer" table="ans1911">
		<id name="id" type="int">
			<column name="ans_id" />
			<generator class="increment" />
		</id>
		<property name="answername"  />
		<property name="postedBy" />
	</class>
</hibernate-mapping>

3) Create the configuration file

This file contains information about the database and mapping file.

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-configuration PUBLIC  
          "-//Hibernate/Hibernate Configuration DTD 5.3//EN"  
          "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd">  
  
<hibernate-configuration>  
  
    <session-factory>  
        <property name="hbm2ddl.auto">create</property>  
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>  
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>  
        <property name="connection.username">system</property>  
        <property name="connection.password">jtp</property>  
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>  
    <mapping resource="question.hbm.xml"/>  
    <mapping resource="answer.hbm.xml"/>
    </session-factory>  
  
</hibernate-configuration>  

4) Create the class to store the data

StoreData.java

package com.javatpoint;  
import java.util.ArrayList;  
import org.hibernate.*;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
   
public class StoreData {  
public static void main(String[] args) {  
   
	StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();  
    Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();  
    SessionFactory factory=meta.getSessionFactoryBuilder().build();  
    Session session=factory.openSession();  
    Transaction t=session.beginTransaction();    
        
	Answer ans1=new Answer();
	ans1.setAnswername("Java is a programming language");
	ans1.setPostedBy("Ravi Malik");
	
	Answer ans2=new Answer();
	ans2.setAnswername("Java is a platform");
	ans2.setPostedBy("Sudhir Kumar");
   
	Question q1=new Question();
	q1.setQname("What is Java?");
	ArrayList<Answer> l1=new ArrayList<Answer>();
	l1.add(ans1);
	l1.add(ans2);
	q1.setAnswers(l1);
	
	Answer ans3=new Answer();  
	ans3.setAnswername("Servlet is an Interface");  
	ans3.setPostedBy("Jai Kumar");  
	      
	Answer ans4=new Answer();  
	ans4.setAnswername("Servlet is an API");  
	ans4.setPostedBy("Arun");  
	
	Question q2=new Question();
	q2.setQname("What is Servlet?");
	ArrayList<Answer> l2=new ArrayList<Answer>();
	l2.add(ans3);
	l2.add(ans4);
	q2.setAnswers(l2);
    session.persist(q1);  
    session.persist(q2);  
      
    t.commit();  
    session.close();  
    System.out.println("success");      
}  
}  