Modifying pom.xml File 📁
Pom.xml: Apache Maven is a popular software project management and comprehension tool built on a standard piece of information known as the Project Object Model (POM). Maven-based projects acquire their compilation, build, reporting, and documentation instructions from an XML file called pom.xml.
Click source in the pom.xml file. Insert the dependencies listed below between the dependencies>....</dependencies> tags. These dependencies are used in Maven projects to add .jar files.
<dependencies>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.13</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.3.7.Final</version>
</dependency>
</dependencies>
<build>
<sourceDirectory>src/main/java</sourceDirectory>
</build>
Configuration File 📁
This file provides database and mapping file information.
hibernate.cfg.xml
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- JDBC Database connection settings -->
<property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate_db</property>
<property name="connection.username">root</property>
<property name="connection.password">root</property>
<!-- JDBC connection pool settings ... using built-in test pool -->
<property name="connection.pool_size">2</property>
<property name="hbm2ddl.auto">update</property>
<!-- dbcp connection pool configuration -->
<property name="hibernate.dbcp.initialSize">5</property>
<property name="hibernate.dbcp.maxTotal">20</property>
<property name="hibernate.dbcp.maxIdle">10</property>
<property name="hibernate.dbcp.minIdle">5</property>
<property name="hibernate.dbcp.maxWaitMillis">-1</property>
<!-- Select our SQL dialect -->
<property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
<!-- Set the current session context -->
<property name="current_session_context_class">thread</property>
<!-- Mapping classes -->
<mapping class="com.codingninjas.Types" />
<mapping class="com.codingninjas.Languages" />
</session-factory>
</hibernate-configuration>
Classes to Store And Fetch Data 🗃️
We define two user classes named DataStore.java and DataFetch.java to store and fetch data to show One to Many mapping.
DataStore.java
package com.codingninjas;
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 DataStore {
public static void main(String[] args) {
StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure().build();
Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();
SessionFactory factory=meta.getSessionFactoryBuilder().build();
Session session=factory.openSession();
Transaction t=session.beginTransaction();
Languages l1 = new Languages("C++", "Bjarne Stroustrup");
Languages l2 = new Languages("Java", "James Gosling");
Languages l3 = new Languages("perl", "Larry Wall");
Languages l4 = new Languages("JavaScript", "Brendan Eich");
ArrayList<Languages> list1 = new ArrayList<Languages>();
list1.add(l1);
list1.add(l2);
ArrayList<Languages> list2 = new ArrayList<Languages>();
list2.add(l3);
list2.add(l4);
Types type1 = new Types();
type1.setLangType("Programming");
type1.setLanguages(list1);
Types type2 = new Types();
type2.setLangType("Scripting");
type2.setLanguages(list2);
session.persist(type1);
session.persist(type2);
t.commit();
session.close();
System.out.println("success");
}
}
You can also try this code with Online Java Compiler
The above program creates two different tables into the database and adds the data to them.
Table1 (types)
Table2 (Languages)
DataFetch.java
To retrieve every record in the Type class, including the languages, we used HQL. In this instance, it fetches the data from two functionally related tables and prints it on screen.
package com.codingninjas;
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 DataFetch {
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 Types");
List<Types> list=query.getResultList();
Iterator<Types> itr=list.iterator();
while(itr.hasNext()){
Types t=itr.next();
System.out.println("Language Type: "+t.getLangType());
//printing answers
List<Languages> list2 = t.getLanguages();
Iterator<Languages> itr2 = list2.iterator();
while(itr2.hasNext())
{
Languages l = itr2.next();
System.out.println(l.getLanguangeName() + ", Developed by: " + l.getDeveloper());
}
}
session.close();
System.out.println("success");
}
}
You can also try this code with Online Java Compiler
Output
Frequently Asked Questions
What is a Persistent Entity?
A persistent entity represents one database row and is always related to some unique hibernate session. Changes to persistent objects are tracked by Hibernate and are saved into the database when commit calls occur.
What is JPQL?
The JPA specification is known as the Java Persistence Query Language (JPQL). When constructing the query, it is used.
What is a Session?
It keeps the database and the Hibernate application connected. It offers factory methods that return these instances because it is a factory for Query, Criteria, and Transaction.
Conclusion
In this article, we have extensively discussed the One to Many mapping in hibernate using annotation, its example, and file modifications in hibernate project structure.
If you think this blog has helped you enhance your knowledge about One to Many mapping and if you would like to learn more, check out our articles Hibernate annotations, One To One Annotation, Many To One Annotation and Many to Many Annotations.
Refer to our Guided Path on Coding Ninjas Studio to upskill yourself in Data Structures and Algorithms, Competitive Programming, JavaScript, System Design, and many more! If you want to test your competency in coding, you may check out the mock test series and participate in the contests hosted on Coding Ninjas Studio! But suppose you have just started your learning process and are looking for questions asked by tech giants like Amazon, Microsoft, Uber, etc. In that case, you must look at the problems, interview experiences, and interview bundle for placement preparations.
Do upvote our blogs if you find them helpful and engaging!
Happy Learning!
26+ registered 
