Hibernate One to Many Example using Annotation

In this section, we will perform one-to-many association to map the list object of persistent class using annotation.

Here, we are using the scenario of Forum where one question has multiple answers.

In such case, there can be many answers for a question and each answer may have its own information that is why we have used list in the persistent class (containing the reference of Answer class) to represent a collection of answers.

Example of One to Many mapping using annotation

1) Create the Persistent class

This persistent class defines properties of the class including List.

Question.java

package com.javatpoint;  
import javax.persistence.*;
import java.util.List;  

@Entity
@Table(name="q5991")
public class Question {  

@Id	
@GeneratedValue(strategy=GenerationType.TABLE)
private int id;  
private String qname;  

@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name="qid")
@OrderColumn(name="type")
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="ans5991")
	public class Answer { 
    @Id
    @GeneratedValue(strategy=GenerationType.TABLE)
    
	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">update</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"/> 
    </session-factory>  
  
</hibernate-configuration>  

4) Create the class to store the data

In this class we are storing the data of the question class.

package com.javatpoint;  

import java.util.ArrayList;  

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
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");  
      
    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");  
      
    ArrayList<Answer> list1=new ArrayList<Answer>();  
    list1.add(ans1);  
    list1.add(ans2);  
      
    ArrayList<Answer> list2=new ArrayList<Answer>();  
    list2.add(ans3);  
    list2.add(ans4);  
      
    Question question1=new Question();  
    question1.setQname("What is Java?");  
    question1.setAnswers(list1);  
      
    Question question2=new Question();  
    question2.setQname("What is Servlet?");  
    question2.setAnswers(list2);  
      
    session.persist(question1);  
    session.persist(question2);  
      
    t.commit();  
    session.close();  
    System.out.println("success");  
}  
} 

Note - Using these annotations in a similar way, we can also perform one-to-many association for set, map and bag objects.

Output

Hibernate One to Many Example using Annotation 1

Hibernate One to Many Example using Annotation 2

How to fetch the data of List

Here, we have used HQL to fetch all the records of Question class including answers. In such case, it fetches the data from two tables that are functional dependent.

package com.javatpoint;  
import java.util.*;
import javax.persistence.TypedQuery;
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 FetchData {  
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();
      
    TypedQuery query=session.createQuery("from Question");  
    List<Question> list=query.getResultList();  
      
    Iterator<Question> itr=list.iterator();  
    while(itr.hasNext()){  
        Question q=itr.next();  
        System.out.println("Question Name: "+q.getQname());  
          
        //printing answers  
        List<Answer> list2=q.getAnswers();  
        Iterator<Answer> itr2=list2.iterator();  
       while(itr2.hasNext())
       {
        Answer a=itr2.next();
            System.out.println(a.getAnswername()+":"+a.getPostedBy());
        }  
    }
    session.close();  
    System.out.println("success");  
}  
}  