Hibernate One-to-Many XML Mapping Example

Oct 17, 2014 by Mukesh Kumar at 3:47 pm

In this tutorial we are going to understand how 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:

In this relationship,one row in a table can be mapped to multiple rows in another table. For example, think of a Bank where we have another table for Customer. A Bank can have multiple Customers, so here we can implement one-to-many Mapping.

Create Tables :

For this example, we used MYSQL Database. Create following two tables in MySQL.Each Bank can be associated with multiple Customer.

One-to-Many Mapping

Create Tables :

For this example, we used MYSQL Database. Create following two tables in MySQL.Each Bank can be associated with multiple Customer.

One-to-Many Mapping

CREATE TABLE `BANK` (
    `bank_id` BIGINT(20) NOT NULL AUTO_INCREMENT,
    `bank_name` VARCHAR(50) NOT NULL DEFAULT '0',
    PRIMARY KEY (`bank_id`)
);

CREATE TABLE `CUSTOMER` (
    `customer_id` BIGINT(10) NOT NULL AUTO_INCREMENT,
    `firstname` VARCHAR(50) NULL DEFAULT NULL,
    `lastname` VARCHAR(50) NULL DEFAULT NULL,
    `birth_date` DATE NULL DEFAULT NULL,
    `cell_phone` VARCHAR(15) NULL DEFAULT NULL,
    `bank_id` BIGINT(20) NULL DEFAULT NULL,
    PRIMARY KEY (`customer_id`),
    INDEX `FK_DEPT` (`bank_id`),
    CONSTRAINT `FK_BANK` FOREIGN KEY (`bank_id`) REFERENCES `bank` (`bank_id`)
);

Project Structure :

Create a simple java project in Eclipse, and add hibernate related jar files to the classpath of the project. The final project structure is given below.

One-to-Many Mapping

Create Model Classes :

Create two Pojo classes Bank.java and Customer.java to model the two tables BANK and CUSTOMER, respectively.

Bank.java

package com.javawebtutor.hibernate.model;

import java.util.Set;

public class Bank {

	private Long bankId;

	private String bankName;

	private Set<Customer> customers;

	public Long getBankId() {
		return bankId;
	}

	public void setBankId(Long bankId) {
		this.bankId = bankId;
	}

	public String getBankName() {
		return bankName;
	}

	public void setBankName(String bankName) {
		this.bankName = bankName;
	}

	public Set<Customer> getCustomers() {
		return customers;
	}

	public void setCustomers(Set<Customer> customers) {
		this.customers = customers;
	}

}

I am using Set of Customers, so that every record is unique. We can also use List or Array for one-to-one mapping.

Customer.java

package com.javawebtutor.hibernate.model;

import java.util.Date;

public class Customer {

	private Long customerId;
	private String firstname;
	private String lastname;
	private Date birthDate;
	private String cellphone;
	private Bank bank;

	public Customer(String firstname, String lastname, Date birthDate,
			String cellphone) {
		this.firstname = firstname;
		this.lastname = lastname;
		this.birthDate = birthDate;
		this.cellphone = cellphone;
	}

	public Long getCustomerId() {
		return customerId;
	}

	public void setCustomerId(Long customerId) {
		this.customerId = customerId;
	}

	public String getFirstname() {
		return firstname;
	}

	public void setFirstname(String firstname) {
		this.firstname = firstname;
	}

	public String getLastname() {
		return lastname;
	}

	public void setLastname(String lastname) {
		this.lastname = lastname;
	}

	public Date getBirthDate() {
		return birthDate;
	}

	public void setBirthDate(Date birthDate) {
		this.birthDate = birthDate;
	}

	public String getCellphone() {
		return cellphone;
	}

	public void setCellphone(String cellphone) {
		this.cellphone = cellphone;
	}

	public Bank getBank() {
		return bank;
	}

	public void setBank(Bank bank) {
		this.bank = bank;
	}

}

Hibernate Utility Class :

Create a utility class for creating Hibernate SessionFactory.

HibernateUtil.java

package com.javawebtutor.hibernate.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

	private static final SessionFactory sessionFactory = buildSessionFactory();

	private static SessionFactory buildSessionFactory() {
		try {
			// Create the SessionFactory from hibernate.cfg.xml
			return new Configuration().configure().buildSessionFactory();
		} catch (Throwable ex) {
			System.err.println("SessionFactory creation failed." + ex);
			throw new ExceptionInInitializerError(ex);
		}
	}

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

Create Hibernate Mapping Files :

Create two XML files bank.hbm.xml and customer.hbm.xml to map the JavaBean classes with the database tables.

bank.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.javawebtutor.hibernate.model">

	<class name="Bank" table="BANK">

		<id name="bankId" type="java.lang.Long" column="department_id">
			<generator class="native" />
		</id>

		<property name="bankName" column="bank_name" />

		<set name="customers" table="CUSTOMER" inverse="true" lazy="true"
			fetch="select">
			<key>
				<column name="bank_id" not-null="true" />
			</key>
			<one-to-many class="com.javawebtutor.hibernate.model.Customer" />
		</set>

	</class>
</hibernate-mapping>

customer.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.javawebtutor.hibernate.model">

	<class name="Customer" table="CUSTOMER">
		<id name="customerId" column="customer_id">
			<generator class="native" />
		</id>

		<property name="firstname" />
		<property name="lastname" column="lastname" />
		<property name="birthDate" type="date" column="birth_date" />
		<property name="cellphone" column="cell_phone" />


		<many-to-one name="bank" class="com.javawebtutor.hibernate.model.Bank"
			fetch="select">
			<column name="bank_id" not-null="true" />
		</many-to-one>

	</class>
</hibernate-mapping>

Create Hibernate Configuration File:

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

hibernate.cfg.xml


<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
	<session-factory>
		<!-- specify database driver -->
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.url"> jdbc:mysql://localhost/hibernate</property>
		<!-- database username -->
		<property name="hibernate.connection.username">root</property>
		<!-- database password -->
		<property name="connection.password">mukesh</property>
		<!-- database dialect, different for different databases -->
		<property name="hibernate.dialect"> org.hibernate.dialect.MySQLDialect</property>
		<!-- true value shows SQL query that is generated by hibrnate -->
		<property name="show_sql">true</property>
		<!-- to bind hibernate session to current running java thread -->
		<property name="current_session_context_class">thread</property>
		<!-- path of hibernate mapping file -->
		<mapping resource="com/javawebtutor/hibernate/model/bank.hbm.xml"></mapping>
		<mapping resource="com/javawebtutor/hibernate/model/customer.hbm.xml"></mapping>
	</session-factory>
</hibernate-configuration>

Note:- Update the database username and password corresponding to your database settings.

Create a Test Program :

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

Test.java

package com.javawebtutor.hibernate.client;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;

import com.javawebtutor.hibernate.model.Bank;
import com.javawebtutor.hibernate.model.Customer;
import com.javawebtutor.hibernate.util.HibernateUtil;

public class Test {
	public static void main(String[] args) {
	
		SessionFactory sf = HibernateUtil.getSessionFactory();
		Session session = sf.openSession();
		session.beginTransaction();

		Bank bank = new Bank();
		bank.setBankName("HDFC");
		session.save(bank);
		Date birthDate = new java.util.Date();
		birthDate = new java.util.Date(83, 02, 22);
		Customer customer = new Customer("Mukesh", "Kumar", birthDate,
				"8939651567");
		Customer customer1 = new Customer("Ravi", "Raj", birthDate, "12345678");
		customer.setBank(bank);
		customer1.setBank(bank);

		session.save(customer);
		session.save(customer1);

		session.getTransaction().commit();
		session.close();
	}
}