Hibernate Many To One(@ManyToOne) association example

Sometime, you have to create the relationships among the various tables or entities when we work in database design. Like, if we consider Book and Author entities, there A book may belongs to one author, but a author can belong to many books.

Here is the hibernate example for this scnario.

package example.configuration.demo6;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Author{

	@Id
	@GeneratedValue
	private int id;
	private String name;
	private String email;
	
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getEmail() {
		return email;
	}
	public void setEmail(String email) {
		this.email = email;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
}

package example.configuration.demo6;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="book")
public class Book {
	
	@Id
	@GeneratedValue
	private int id;
	private String title;
	private float price;
	@ManyToOne
	private Author author;
	
	public float getPrice() {
		return price;
	}
	public void setPrice(float price) {
		this.price = price;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public Author getAuthor() {
		return author;
	}
	public void setAuthor(Author author) {
		this.author = author;
	}
	
}

package example.configuration.demo6;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;


public class MainClass {
	public static void main(String[] args){
		
		StandardServiceRegistry registry=new StandardServiceRegistryBuilder().configure().build();
		SessionFactory factory=new MetadataSources(registry).buildMetadata().buildSessionFactory();
		Session session=factory.openSession();
		
		Transaction tx=session.beginTransaction();
		
		Author author=new Author();
		author.setName("John");
		author.setEmail("john@gmail.com");
		
		Book book=new Book();
		book.setTitle("Learning Hibernate");
		book.setAuthor(author);
		book.setPrice(2342);
		
		
		session.save(author);
		session.save(book);
		tx.commit();
		session.close();
	}
}

<?xml version="1.0" encoding="UTF-8"?>
<!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>
  <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
  <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/demo</property>
  <property name="hibernate.connection.username">root</property>
  <property name="hibernate.dialect">org.hibernate.dialect.MariaDB53Dialect</property>
  <property name="hibernate.hbm2ddl.auto">create</property>
  <property name="hibernate.show_sql">true</property>
  <property name="hibernate.format_sql">true</property>
  <property name="packagesToScan">example</property>
  <mapping class="example.configuration.demo6.Book"/>
  <mapping package="example"/>
  <mapping class="example.configuration.demo6.Author"/>
 </session-factory>
</hibernate-configuration>

Here is the database design created by the above code example;