Hibernate Many to Many Example using Annotation

In the previous section, we have performed many to many mapping using XML file. Here, we are going to perform this task using annotation.

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 by list.

1) Create the Persistent class

Question.java

package com.javatpoint;  
  
import java.util.List;
import javax.persistence.*;  
  
@Entity
@Table(name="ques1123")
public class Question {  
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
private int id;  
private String qname; 

@ManyToMany(targetEntity = Answer.class, cascade = { CascadeType.ALL })
@JoinTable(name = "q_ans1123", 
			joinColumns = { @JoinColumn(name = "q_id") }, 
			inverseJoinColumns = { @JoinColumn(name = "ans_id") })
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 javax.persistence.*;

@Entity
@Table(name="ans1123")
public class Answer { 
	
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
private int id;  
private String answername;  
private String postedBy;  
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;
}

}  

2) Add project information and configuration in pom.xml file.

Open pom.xml file and click source. Now, add the below dependencies between <dependencies>....</dependencies> tag.

<dependency>  
    <groupId>org.hibernate</groupId>  
    <artifactId>hibernate-core</artifactId>  
    <version>5.3.1.Final</version>  
</dependency>  

<dependency>  
    <groupId>com.oracle</groupId>  
    <artifactId>ojdbc14</artifactId>  
    <version>10.2.0.4.0</version>  
</dependency>  

3) Create the configuration file

This file contains information about the database and mapping file.

<?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 class="com.javatpoint.Question"/>  
    <mapping class="com.javatpoint.Answer"/>
    </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 an1=new Answer();
	an1.setAnswername("Java is a programming language");
	an1.setPostedBy("Ravi Malik");
	
	Answer an2=new Answer();
	an2.setAnswername("Java is a platform");
	an2.setPostedBy("Sudhir Kumar");
   
	Question q1=new Question();
	q1.setQname("What is Java?");
	ArrayList<Answer> l1=new ArrayList<Answer>();
	l1.add(an1);
	l1.add(an2);
	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");  
    
     
}  
} 