Hibernate one-to-many relationships.

Hibernate Mapping One-to-Many

Hibernate provides facility of mapping. You can do mapping through hbm.xml or through annotation. Here is an example showing one to many relationship using annotation?

We have two table ?

1. Author.java
2. Book.java

One author can write more than one book..So here is mapping one author to many books.

Author.java

package net.roseindia.table;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name = "author")
public class Author {

    private int id;
    private String name;

    private Set<Book> bookSet = new HashSet<Book>();

    public Author() {

    }

    public Author(String name, Set<Book> book) {
        this.name = name;
        this.bookSet = book;
    }

    @Id
    @GeneratedValue
    @Column(name = "id")
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Column(name = "name")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @OneToMany(cascade = CascadeType.ALL)
    public Set<Book> getBookSet() {
        return bookSet;
    }

    public void setBookSet(Set<Book> bookSet) {
        this.bookSet = bookSet;
    }

}

Book.java

package net.roseindia.table;

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

@Entity
@Table(name = "book")
public class Book {
    private int id;
    private String tile;

    public Book() {

    }

    public Book(String title) {
        this.tile = title;
    }

    @Id
    @GeneratedValue
    @Column(name = "id")
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Column(name = "title")
    public String getTile() {
        return tile;
    }

    public void setTile(String tile) {
        this.tile = tile;
    }

}

Continue....

2. hibernate-cfg.xml is configuration file saved in the same folder where the source code of class file is saved. It creates the connection pool and set-up required environment.

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/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/hibernateRelationShip</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">root</property>
        <property name="hibernate.connection.pool_size">10</property>
        <property name="show_sql">true</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.hbm2ddl.auto">create-drop</property>

        <!-- Mapping files -->
        <mapping class="net.roseindia.table.Book" />
        <mapping class="net.roseindia.table.Author" />

    </session-factory>
</hibernate-configuration>

3.

Now create an util class as HibernateUtil.java.

package net.roseindia.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

public class HibernateUtil {
    private static SessionFactory sessionFactory = null;
    static {
        sessionFactory = new AnnotationConfiguration().configure()
                .buildSessionFactory();
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

4.

Here is your main class-

package net.roseindia.application;

import java.util.HashSet;
import java.util.Set;

import net.roseindia.table.Author;
import net.roseindia.table.Book;
import net.roseindia.util.HibernateUtil;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;

public class OneToManyRelation {

    public static void main(String[] args) {


        Session session = null;
        try {
            session = HibernateUtil.getSessionFactory().openSession();

            Set<Book> books = new HashSet<Book>();
            books.add(new Book("Java"));
            books.add(new Book("C++"));

            Author author = new Author("Ratna", books);

            Transaction tr = session.beginTransaction();
            session.save(author);
            tr.commit();

            System.out.println("Done");

        } catch (HibernateException he) {
            System.out.println(he.getMessage());
        } finally {
                session.close();
        }

    }

}