One to Many XML

Creating the Mapping file

In the below implementation, we will be creating a file named question.hbm.xml 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.codingninjas.Question" table="q501">  
          <id name="id">  
          <generator class="increment"></generator>  
          </id>  
          <property name="qname"></property>  
            
          <list name="answers" cascade="all">  
          <key column="qid"></key>  
          <index column="type"></index>  
          <one-to-many class="com.codingninjas.Answer"/>  
          </list>  
            
          </class>  
            
          <class name="com.codingninjas.Answer" table="ans501">  
          <id name="id">  
          <generator class="increment"></generator>  
          </id>  
          <property name="answername"></property>  
          <property name="postedBy"></property>  
          </class>  
            
          </hibernate-mapping>

Configuration File

This file provides database and mapping file information.

<?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">  
  
<!-- Generated by MyEclipse Hibernate Tools.                   -->  
<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 resource="question.hbm.xml"/>  
    </session-factory>  
  
</hibernate-configuration>  

Classes to Store And Fetch Data

We define two user classes named store.java and fetch.java to store and fetch data in one-to-many mapping respectively.

Store.java

The data from the question class is stored in this class.

package com.codingninjas;    
  
import java.util.ArrayList;    
    
import org.hibernate.SessionFactory;  
import org.hibernate.Session;
import org.hibernate.Transaction;  
import org.hibernate.boot.MetadataSources;  
import org.hibernate.boot.Metadata;  
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;  
import org.hibernate.boot.registry.StandardServiceRegistry;  


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("Orange is a color.");    
    	ans1.setPostedBy("Coder1");    
        	
    	Answer ans2=new Answer();    
    	ans2.setAnswername("Orange is a fruit");    
    	ans2.setPostedBy("Coder2");    
        	
    	Answer ans3=new Answer();    
    	ans3.setAnswername("Averse is a noun");    
    	ans3.setPostedBy("Coder3");    
        	
    	Answer ans4=new Answer();    
    	ans4.setAnswername("Averse is an adjective");    
    	ans4.setPostedBy("Coder4");    
        	
    	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 orange?");    
    	question1.setAnswers(list1);    
        	
    	Question question2=new Question();    
    	question2.setQname("What is averse?");    
    	question2.setAnswers(list2);    
        	
    	session.persist(question1);    
    	session.persist(question2);    
        	
    	t.commit();    
    	session.close();    
    	System.out.println("Done");    
    }    
}   

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Output

Fetch.java

To retrieve every record in the Question class, including the responses, we used HQL. In this instance, it fetches the data from two functionally related tables.

Here, we are directly printing the object of the answer class in this case, but we have overridden the function toString() method in the Answer class, which returns the answername and poster name. As a result, instead of the reference id, it prints the answername and postername.

package com.codingninjas;    
import java.util.*;    
import org.hibernate.*;  
import javax.persistence.TypedQuery;
import org.hibernate.boot.Metadata; 
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;     
import org.hibernate.boot.registry.StandardServiceRegistry;  
import org.hibernate.boot.MetadataSources; 
    
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("Done");    
    }    
}

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Output 

Frequently Asked Questions

How is mapping accomplished in Hibernate?

One of the main components of Hibernate is association mappings. Similar linkages to those in the relational database model are supported. As follows:

• One-to-one relationships
• many-to-one relationships
• many-to-many relationships

What is HQL?

The abbreviation for Hibernate Query Language is HQL. It is a database-independent, object-oriented query language.

What is the One-to-Many association in Hibernate?

In this kind of linkage, a single thing may be connected to numerous other objects. In terms of the mapping, a Set Java collection without any unnecessary elements is used to implement the One-to-Many mapping. The set's One-to-Many element describes the relationship between a single object and many other things.

Conclusion

In this article, we have extensively discussed the One-to-many mapping in hibernate using XML, its example, and file mapping in hibernate project structure.

If you think this blog has helped you enhance your knowledge about One-to-many mapping using XML and if you would like to learn more, check out our articles Hibernate Interview Questions, OOPS in Java, Java Framework, and JDBC Connection.

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