Hibernate one to many mapping example using set

Hibernate one to many mapping example using set

In this tutorial we are going to understand how to use XML to map a one-to-many association between Java objects and database tables using Hibernate framework. We will create a sample Hibernate-based application to manage the following entity relationship:

1. Creating sample database and tables
2. Required Jars for project
3. Coding Hibernate Model Classes
4. Creating Hibernate Mapping Files
5. Writing Hibernate Configuration File
6. Coding a Test Program

1.  Creating sample database and tables

   Execute the following script in MySQL Workbench’s SQL Editor to create a database                     

   called cartdb with two tables named cart and items:

create database cartdb;
use cartdb;
 
CREATE TABLE `cart` (
  `cart_id` int(11) NOT NULL AUTO_INCREMENT,
  `total` int(11) NOT NULL,
  `name` varchar(45) NOT NULL,
  PRIMARY KEY (`cart_id`)
);
 
CREATE TABLE `items` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
   `cart_id` int(11) NOT NULL,
  `item_id` int(11) NOT NULL,
  `item_total` int(11) NOT NULL,
  `quantity` int(11) NOT NULL,
  
  PRIMARY KEY (`id`),
  KEY `fk_cart` (`cart_id`),
  CONSTRAINT `fk_cart` FOREIGN KEY (`cart_id`) REFERENCES `cart` (`cart_id`)
);

2. Required Jars for project

   

hibernate-core-4.2.2.Final.jar
hibernate-commons-annotations-4.0.2.Final.jar
jboss-transaction-api_1.1_spec-1.0.1.Final.jar
hibernate-jpa-2.0-api-1.0.1.Final.jar
jboss-logging-3.1.0.GA.jar
antlr-2.7.7.jar
dom4j-1.6.1.jar
javassist-3.15.0-GA.jar

3. Coding hibernate model classes

Create two JavaBean-style classes Cart.java and Items.java to model the two tables cart and items, respectively.

File net\engineeernitesh\hibernate\Cart.java:

package net.engineeernitesh.hibernate;
 
import java.util.Set;
 
public class Cart {
 
    private long id;
    private long total;
    private String name;
 
    private Set<Items> items;
 
    public Category() {
    }
 
    public Category(Long total,String name) {
     this.total = total;
        this.name = name;
    }
 
    // getters and setters...
 
}

File net\engineeernitesh\hibernate\Items.java:

package net.engineeernitesh.hibernate;
 
public class Items {
    private long id;
    private Cart cart;
    private long item_id;
    private long item_total;
    private long quantity;
     
    public Items() {
    }
 
    public Items(Cart cart,Long item_id,Long item_total,Long quantity) {
        this.cart = cart;
        this.item_id = item_id;
        this.item_total = item_total;
        this.quantity = quantity;
    }
 
 
    // getters and setters...
 
}

4. Creating hibernate mapping files

Create two XML files Cart.hbm.xml and Items.hbm.xml to tell Hibernate how to map the JavaBean classes above with the database tables.

File net\engineeernitesh\hibernate\Cart.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="net.engineeernitesh.hibernate">
    <class name="Cart" table="CART">
        <id name="id" column="CART_ID">
            <generator class="native"/>
        </id>
  <property name="total" column="TOTAL" />
        <property name="name" column="NAME" />
 
        <set name="items" inverse="true" cascade="all">
            <key column="CART_ID" not-null="true" />
            <one-to-many class="Items"/>
        </set>
    </class> 
</hibernate-mapping>

File net\engineeernitesh\hibernate\Items.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="net.engineeernitesh.hibernate">
    <class name="Items" table="ITEMS">
        <id name="id" column="ID">
            <generator class="native"/>
        </id>
  <many-to-one name="cart" class="Cart"
            column="CART_ID" not-null="true"/>
        <property name="item_id" column="ITEM_ID" />
        <property name="item_total" column="ITEM_TOTAL" />
        <property name="quantity" column="QUANTITY" />
                
    </class> 
</hibernate-mapping>

5. Writing Hibernate Configuration File

Create the Hibernate configuration file (hibernate.cfg.xml) to specify database type, connection details and the mapping files:

<?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>
    <!-- Database connection settings -->
    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="connection.url">jdbc:mysql://localhost:3306/cartdb</property>
    <property name="connection.username">root</property>
    <property name="connection.password">secret</property>
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="show_sql">true</property>
     
    <mapping resource="net/codejava/hibernate/Cart.hbm.xml"/>
    <mapping resource="net/codejava/hibernate/Items.hbm.xml"/>
       
  </session-factory>
</hibernate-configuration>

6. Coding a Test Program

Following is code of the test program that persists some sample data:

package net.engineeernitesh.hibernate;
 
import java.util.HashSet;
import java.util.Set;
 
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
 
/**
 *
 * This program demonstrates using Hibernate framework to manage a
 * bidirectional one-to-many association.
 * @author www.engineeernitesh.blogspot
 *
 */
public class CartManager {
 
    public static void main(String[] args) {
        // loads configuration and mappings
        Configuration configuration = new Configuration().configure();
        ServiceRegistryBuilder registry = new ServiceRegistryBuilder();
        registry.applySettings(configuration.getProperties());
        ServiceRegistry serviceRegistry = registry.buildServiceRegistry();
         
        // builds a session factory from the service registry
        SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
         
        // obtains the session
        Session session = sessionFactory.openSession();
        session.beginTransaction();
         
        Cart cart = new Cart(2,"Shopping");
         
        Items bag = new Items(cart,1,2,5);
  
        Items book = new Items(cart,2,4,5);
         
             
        Set<Items> items = new HashSet<Items>();
        items.add(bag);
        items.add(book);
                 
        cart.setItems(items);
         
        session.save(cart);
         
        session.getTransaction().commit();
        session.close();       
    }
}

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