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Let us understand how One-to-one mapping works in Hibernate. Following is a simply yet concept building example where we will understand One-to-one mapping in Hibernate framework using XML Mappings. We will use two tables “employee” and “employeedetail” which exhibits one-to-one relationship. Using Hibernate we will implement this relationship. [sc name=”Hibernate_Tutorials”] Tools and technologies used in this article:

1. Java JDK 1.5 above
2. MySQL 5 above
3. Eclipse 3.2 above
4. Hibernate 3 above
5. Maven 3 above

1. Create Database

We will use MySQL in our example. Create two tables “employee” and “employeedetail” with One-to-one relationship. Following is the SQL script for same.

/* EMPLOYEE table */
CREATE TABLE `employee` (
 `employee_id` BIGINT(10) NOT NULL AUTO_INCREMENT,
 `firstname` VARCHAR(50) NULL DEFAULT NULL,
 `lastname` VARCHAR(50) NULL DEFAULT NULL,
 `birth_date` DATE NOT NULL,
 `cell_phone` VARCHAR(15) NOT NULL,
 PRIMARY KEY (`employee_id`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
ROW_FORMAT=DEFAULT
AUTO_INCREMENT=216



/* EMPLOYEEDETAIL table */
CREATE TABLE `employeedetail` (
 `employee_id` BIGINT(20) NOT NULL AUTO_INCREMENT,
 `street` VARCHAR(50) NULL DEFAULT NULL,
 `city` VARCHAR(50) NULL DEFAULT NULL,
 `state` VARCHAR(50) NULL DEFAULT NULL,
 `country` VARCHAR(50) NULL DEFAULT NULL,
 PRIMARY KEY (`employee_id`),
 CONSTRAINT `FKEMPL` FOREIGN KEY (`employee_id`) REFERENCES `employee` (`employee_id`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
ROW_FORMAT=DEFAULT
AUTO_INCREMENT=216

Code language: SQL (Structured Query Language) (sql)

Note that a one-to-one relationships occurs when one entity is related to exactly one occurrence in another entity. Thus, there will be one primary key which will be mapped with both the entities.

2. Hibernate Maven dependency

Following dependencies we will use in Maven which will add Hibernate support. File: /pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>net.viralpatel.hibernate</groupId>
 <artifactId>HibernateHelloWorldXML</artifactId>
 <packaging>jar</packaging>
 <version>1.0-SNAPSHOT</version>
 <name>HibernateHelloWorldXML</name>
 <url>http://maven.apache.org</url>
 <dependencies>
  <dependency>
   <groupId>mysql</groupId>
   <artifactId>mysql-connector-java</artifactId>
   <version>5.1.10</version>
  </dependency>
  <dependency>
   <groupId>org.hibernate</groupId>
   <artifactId>hibernate</artifactId>
   <version>3.2.6.ga</version>
  </dependency>
 </dependencies>
</project>
Code language: HTML, XML (xml)

3. Hibernate Model class

For this example we will create two Model class: Employee.java and EmployeeDetail.java. Add following in your project. File: /src/main/java/net/viralpatel/hibernate/Employee.java

package net.viralpatel.hibernate;

import java.sql.Date;

public class Employee {

 private Long employeeId;
 private String firstname;
 private String lastname;
 private Date birthDate;
 private String cellphone;
 private EmployeeDetail employeeDetail;

 public Employee() {

 }

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

 // Getter and Setter methods 
}
Code language: Java (java)

File: /src/main/java/net/viralpatel/hibernate/EmployeeDetail.java

package net.viralpatel.hibernate;

public class EmployeeDetail {

 private Long employeeId;
 private String street;
 private String city;
 private String state;
 private String country;

 private Employee employee;

 public EmployeeDetail() {

 }

 public EmployeeDetail(String street, String city, String state, String country) {
  this.street = street;
  this.city = city;
  this.state = state;
  this.country = country;
 }
 
 // Getter and Setter methods 

}
Code language: Java (java)

Note that in above model classes, employeeId is common. This is the primary key of Employee table that exhibits One-to-one relationship with EmployeeDetail table.

4. Hibernate XML Mapping (HBM)

Add following hibernate mapping (hbm) files Employee.hbm.xml and EmployeeDetail.hbm.xml for the model classes created in above steps. File: /src/main/java/net/viralpatel/hibernate/Employee.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="net.viralpatel.hibernate">

 <class name="Employee" table="EMPLOYEE">
  <id name="employeeId" column="EMPLOYEE_ID">
   <generator class="native" />
  </id>
  <one-to-one name="employeeDetail" class="net.viralpatel.hibernate.EmployeeDetail"
   cascade="save-update"></one-to-one>
  
  <property name="firstname" />
  <property name="lastname" column="lastname" />
  <property name="birthDate" type="date" column="birth_date" />
  <property name="cellphone" column="cell_phone" />

 </class>
</hibernate-mapping>
Code language: HTML, XML (xml)

File: /src/main/java/net/viralpatel/hibernate/EmployeeDetail.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="net.viralpatel.hibernate">

    <class name="EmployeeDetail" table="EMPLOYEEDETAIL">

   <id name="employeeId" type="java.lang.Long">
   <column name="EMPLOYEE_ID" />
   <generator class="foreign">
    <param name="property">employee</param>
   </generator>
  </id>
  <one-to-one name="employee" class="net.viralpatel.hibernate.Employee"
   constrained="true"></one-to-one>
  
        <property name="street" column="STREET"/>
        <property name="city" column="CITY"/>
        <property name="state" column="STATE"/>
        <property name="country" column="COUNTRY"/>
 </class>

</hibernate-mapping>
Code language: HTML, XML (xml)

Note that in above hibernate mapping we are implementing One-to-one relationship. For both the model classes we are using a single primary key EmployeeId. In EmployeeDetail hbm file we have defined a foreign identifier generator so that primary it uses primary key of Employee table.

5. Hibernate Configuration

Following is the hibernate configuration hibernate.cfg.xml file. Add this in your project. File: /src/main/resources/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>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/tutorial</property>
        <property name="connection.username">root</property>
        <property name="connection.password"></property>
        
        <property name="connection.pool_size">1</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="current_session_context_class">thread</property>
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
        <property name="show_sql">true</property>
        <property name="hbm2ddl.auto">validate</property>
 
        <mapping resource="net/viralpatel/hibernate/EmployeeDetail.hbm.xml"/>
        <mapping resource="net/viralpatel/hibernate/Employee.hbm.xml"/>
    
    </session-factory>
</hibernate-configuration>
Code language: HTML, XML (xml)

6. Hibernate Utility class

File:/src/main/java/net/viralpatel/hibernate/HibernateUtil.java

package net.viralpatel.hibernate;
 
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("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }
 
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

Code language: Java (java)

7. Main class to test One-to-one mapping

Add following Main.java class in your project to test One-to-one relationship mapping functionality. File:/src/main/java/net/viralpatel/hibernate/Main.java

package net.viralpatel.hibernate;

import java.sql.Date;
import java.util.List;

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

public class Main {

 public static void main(String[] args) {

  SessionFactory sf = HibernateUtil.getSessionFactory();
  Session session = sf.openSession();
  session.beginTransaction();

  EmployeeDetail employeeDetail = new EmployeeDetail("10th Street", "LA", "San Francisco", "U.S.");
  
  Employee employee = new Employee("Nina", "Mayers", new Date(121212),
    "114-857-965");
  employee.setEmployeeDetail(employeeDetail);
  employeeDetail.setEmployee(employee);
  
  
  session.save(employee);

  
  List<Employee> employees = session.createQuery("from Employee").list();
  for (Employee employee1 : employees) {
   System.out.println(employee1.getFirstname() + " , "
     + employee1.getLastname() + ", "
     + employee1.getEmployeeDetail().getState());
  }

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

 }
}
Code language: Java (java)

8. Review Project Structure

Below is the final project structure with all the source files.

8. Execute the example

Execute the Main class. Hibernate will insert a row in Employee and EmployeeDetail table. Output:

Hibernate: insert into EMPLOYEE (firstname, lastname, birth_date, cell_phone) values (?, ?, ?, ?)
Hibernate: insert into EMPLOYEEDETAIL (STREET, CITY, STATE, COUNTRY, EMPLOYEE_ID) values (?, ?, ?, ?, ?)
Hibernate: select employee0_.EMPLOYEE_ID as EMPLOYEE1_1_, employee0_.firstname as firstname1_, employee0_.lastname as lastname1_, employee0_.birth_date as birth4_1_, employee0_.cell_phone as cell5_1_ from EMPLOYEE employee0_
Hibernate: select employeede0_.EMPLOYEE_ID as EMPLOYEE1_0_0_, employeede0_.STREET as STREET0_0_, employeede0_.CITY as CITY0_0_, employeede0_.STATE as STATE0_0_, employeede0_.COUNTRY as COUNTRY0_0_ from EMPLOYEEDETAIL employeede0_ where employeede0_.EMPLOYEE_ID=?
Nina , Mayers, San Francisco
Code language: HTML, XML (xml)

That’s All Folks

Today we saw how to write Hibernate program and implements One-to-one relationship mapping using XML mappings. We used Maven to generate Java project and added Hibernate dependencies into it.

Download Source

Hibernate-One-to-one-tutorial-XML-Mapping.zip (9 kb)