Hibernate – One-to-One example (XML Mapping)

A one-to-one relationships occurs when one entity is related to exactly one occurrence in another entity.

In this tutorial, we show you how to work with one-to-one table relationship in Hibernate, via XML mapping file (hbm).

Tools and technologies used in this tutorials :

Hibernate 3.6.3.Final

MySQL 5.1.15

Maven 3.0.3

Eclipse 3.6

Project Structure

See the final project structure of this tutorial.

Project Dependency

Get

hibernate.jar

from JBoss repository, Maven will take care all the related dependencies for you.

File :

pom.xml

<project ...>

<repositories>
<repository>
<id>JBoss repository</id>
<url>http://repository.jboss.org/nexus/content/groups/public/</url>
</repository>
</repositories>

<dependencies>

<!-- MySQL database driver -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.15</version>
</dependency>

<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>3.6.3.Final</version>
</dependency>

<dependency>
<groupId>javassist</groupId>
<artifactId>javassist</artifactId>
<version>3.12.1.GA</version>
</dependency>

</dependencies>
</project>

1. “One-to-one” table relationship

A one-to-one relationship table design, a

STOCK

table contains exactly one record in

STOCK_DETAIL

table. Both tables have the same

Stock_Id

as primary key. In

STOCK_DETAIL

table,

Stock_Id

is the primary key and also a foreign key to

STOCK

table. This is the common way of define “one-to-one” table relationship.

2. Hibernate Model Class

Create two model classes –

Stock.java

and

StockDetail.java

, to represent the above tables.

File :

Stock.java

package com.mkyong.stock;

public class Stock implements java.io.Serializable {

private Integer stockId;
private String stockCode;
private String stockName;
private StockDetail stockDetail;

//constructor & getter and setter methods

}

File :

StockDetail.java

package com.mkyong.stock;

public class StockDetail implements java.io.Serializable {

private Integer stockId;
private Stock stock;
private String compName;
private String compDesc;
private String remark;
private Date listedDate;

//constructor & getter and setter methods

}

3. Hibernate XML Mapping

Now, create two Hibernate mapping files (hbm) –

Stock.hbm.xml

and

StockDetail.hbm.xml

.

File :

Stock.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 25 April 2011 7:52:33 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
<class name="com.mkyong.stock.Stock" table="stock" catalog="mkyongdb">
<id name="stockId" type="java.lang.Integer">
<column name="STOCK_ID" />
<generator class="identity" />
</id>
<property name="stockCode" type="string">
<column name="STOCK_CODE" length="10" not-null="true" unique="true" />
</property>
<property name="stockName" type="string">
<column name="STOCK_NAME" length="20" not-null="true" unique="true" />
</property>
<one-to-one name="stockDetail" class="com.mkyong.stock.StockDetail"
cascade="save-update"></one-to-one>
</class>
</hibernate-mapping>

File :

StockDetail.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 25 April 2011 7:52:33 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
<class name="com.mkyong.stock.StockDetail" table="stock_detail"
catalog="mkyongdb">
<id name="stockId" type="java.lang.Integer">
<column name="STOCK_ID" />
<generator class="foreign">
<param name="property">stock</param>
</generator>
</id>
<one-to-one name="stock" class="com.mkyong.stock.Stock"
constrained="true"></one-to-one>
<property name="compName" type="string">
<column name="COMP_NAME" length="100" not-null="true" />
</property>
<property name="compDesc" type="string">
<column name="COMP_DESC" not-null="true" />
</property>
<property name="remark" type="string">
<column name="REMARK" not-null="true" />
</property>
<property name="listedDate" type="date">
<column name="LISTED_DATE" length="10" not-null="true" />
</property>
</class>
</hibernate-mapping>

Note

The main difficulty in this one-to-one relationship is ensuring both are assigned the same primary key. In

StockDetail.hbm.xml

, a special foreign identifier generator is declared, it will know get the primary key value from

STOCK

table. With

constrained=”true”

, it ensure the

Stock

must exists.

4. Hibernate Configuration File

Puts

Stock.hbm.xml

and

StockDetail.hbm.xml

in your Hibernate configuration file, and also MySQL connection details.

File :

hibernate.cfg.xml

<?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>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/mkyongdb</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">password</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<mapping resource="com/mkyong/stock/Stock.hbm.xml" />
<mapping resource="com/mkyong/stock/StockDetail.hbm.xml" />
</session-factory>
</hibernate-configuration>

5. Run It

Run it, Hibernate will insert a row into the

STOCK

table and a row into the

STOCK_DETAIL

table.

File :

App.java

package com.mkyong;

import java.util.Date;
import org.hibernate.Session;
import com.mkyong.stock.Stock;
import com.mkyong.stock.StockDetail;
import com.mkyong.util.HibernateUtil;

public class App {
public static void main(String[] args) {
System.out.println("Hibernate one to one (XML mapping)");
Session session = HibernateUtil.getSessionFactory().openSession();

session.beginTransaction();

Stock stock = new Stock();

stock.setStockCode("4715");
stock.setStockName("GENM");

StockDetail stockDetail = new StockDetail();
stockDetail.setCompName("GENTING Malaysia");
stockDetail.setCompDesc("Best resort in the world");
stockDetail.setRemark("Nothing Special");
stockDetail.setListedDate(new Date());

stock.setStockDetail(stockDetail);
stockDetail.setStock(stock);

session.save(stock);
session.getTransaction().commit();

System.out.println("Done");
}
}

Output

Hibernate one to one (XML mapping)
Hibernate: insert into mkyongdb.stock (STOCK_CODE, STOCK_NAME) values (?, ?)
Hibernate: insert into mkyongdb.stock_detail
(COMP_NAME, COMP_DESC, REMARK, LISTED_DATE, STOCK_ID) values (?, ?, ?, ?, ?)

Done