Hibernate Component Tag, Object Composition using Hibernate, using Hibernate component mapping, Usage, Tutorial, Property component

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In this Page we shall be covering a simple example on how to use component
tag for persisting object with composition of other objects with it. 
By composition I mean, if the parent object dies , then the contained child
object(s) will die too. 
Hibernate has a provision for achieving this by using a tag 'component' 
that can be used under class tag for configuring a class hierarchy as follows:

Visitor
 |------>VisitorDetails
             |------------>Address
             












Visitor.java
package com.techienjoy.hibernate.example;

public class Visitor {

    long id;
    VisitorDetails details;

    public VisitorDetails getDetails() {
        return details;
    }


    public long getId() {
        return id;
    }


    public void setId(long id) {
        this.id = id;
    }


    public void setDetails(VisitorDetails details) {
        this.details = details;
    }
}


VisitorDetails.java
package com.techienjoy.hibernate.example;

public class VisitorDetails {
    String name;
    Address address;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Address getAddress() {
        return address;
    }
    public void setAddress(Address address) {
        this.address = address;
    }
}


VisitorDetails.java
package com.techienjoy.hibernate.example;

public class Address {

    String houseNumber;
    String addrLine1;
    String addrLine2;
    String phone;
    public String getHouseNumber() {
        return houseNumber;
    }
    public void setHouseNumber(String houseNumber) {
        this.houseNumber = houseNumber;
    }
    public String getAddrLine1() {
        return addrLine1;
    }
    public void setAddrLine1(String addrLine1) {
        this.addrLine1 = addrLine1;
    }
    public String getAddrLine2() {
        return addrLine2;
    }
    public void setAddrLine2(String addrLine2) {
        this.addrLine2 = addrLine2;
    }
    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }
}



Visitor.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">
<hibernate-mapping package="com.techienjoy.hibernate.example">
   <class name="Visitor" table="VISITOR">
    <id name="id" type="long" column="ID"/>
    <component name="details" class="VisitorDetails">
      <property name="name" column="NAME"/>
      <component name="address" class="Address">
        <property name="houseNumber" column="HOUSE_NUMBER" not-null="true"/>
        <property name="addrLine1" column="ADDRLINE1"/>
        <property name="addrLine2" column="ADDRLINE2"/>
        <property name="phone" column="PHONE"/>
      </component>
    </component>
   </class>
</hibernate-mapping>


Testing this example can be done using following Test Harness Code:
Test.java
package com.techienjoy.hibernate.example;

/**
 * This code is provided on "AS IS" basis, without warranty
 * or guaranty of any kind.
 * Author : TechIEnjoy
 * Date: 28-November-2010
 */
import java.math.BigDecimal;

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

public class Test {

    private static SessionFactory sessionFactory;

    /**
     * @param args
     */
    public static void main(String[] args) {

        try {
            sessionFactory = new Configuration().configure()
                    .buildSessionFactory();

            Address address = new Address();
            address.setHouseNumber("HS/001");
            address.setAddrLine1("Address Line 1");
            address.setAddrLine2("Adress Line 2");
            address.setPhone("3234-98878");
            VisitorDetails visitorDetails = new VisitorDetails();
            visitorDetails.setName("Visitor Johney");
            visitorDetails.setAddress(address);
            Visitor visitor = new Visitor();
            visitor.setDetails(visitorDetails);
            
            Session session = sessionFactory.openSession();
            Transaction tx = session.beginTransaction();
            tx.begin();
            session.saveOrUpdate(visitor);
            session.delete(visitor);
            tx.commit();
            session.close();
            
        } catch (Exception ex) {
            ex.printStackTrace();
        }

    }

}


On execution of this test code, we can have a table automatically created and 
populated with values as defined in the Test code.
And on deleting visitor object from database, we would see that the complete
row/record corresponding to this object is getting deleted, thus leaving no
chance for retrieving Address object alone. Is this not a composition of 
objects as we know it!!




Hope this helps.


If anything missed out , please let me know at
techienjoy at yahoo . com