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:
- Creating sample database and tables
- Required Jars for project
- Coding Hibernate Model Classes
- Creating Hibernate Mapping Files
- Writing Hibernate Configuration File
- Coding a Test Program
- 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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