HIBERNATE 4U: Hibernate Component Mapping

In this example you will learn how to map components using Hibernate. Consider the following relationship between Student and Address entity.

According to the relationship each student should have a unique address.
Since the Student and Address entities are strongly related (composition relation), it is better to store them in a single table. The relational model is shown below.

Student.hbm.xml is used to create the STUDENT table.

xml  version="1.0"?>

"-//Hibernate/Hibernate  Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class  name="com.vaannila.student.Student" table="STUDENT">
        <meta  attribute="class-description">This  class contains student details.meta>
        <id name="studentId" type="long" column="STUDENT_ID">
            <generator class="native" />
        id>
        <property name="studentName" type="string" not-null="true"
            column="STUDENT_NAME" />
        <component  name="studentAddress" class="com.vaannila.student.Address">
            <property name="street" column="ADDRESS_STREET" type="string"
                length="250" />
            <property name="city" column="ADDRESS_CITY" type="string"
                length="50" />
            <property name="state" column="ADDRESS_STATE" type="string"
                length="50" />
            <property name="zipcode" column="ADDRESS_ZIPCODE" type="string"
                length="10" />
        component>
    class>
hibernate-mapping>

The component element is used to map all the Address entity fields to the STUDENT table. In Hibernate terms the Address entity is called the component and it cannot have its own primary key, it uses the primary key of the enclosing Student entity.

Now create the hibernate configuration file.

"1.0" encoding="UTF-8"?>

        "-//Hibernate/Hibernate  Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

    
        "hibernate.connection.driver_class"> org.hsqldb.jdbcDriver
        "hibernate.connection.url">  jdbc:hsqldb:hsql://localhost
        "hibernate.connection.username">sa
        "connection.password">
        "connection.pool_size">1
        "hibernate.dialect">  org.hibernate.dialect.HSQLDialect
        "show_sql">true
        "hbm2ddl.auto">create-drop
        "com/vaannila/student/Student.hbm.xml"/>
    


After creating the configuration file, generate java class files using Hibernate Tools.(To generate code using Hibernate Tools refer this example )
The following classes will be generated. You will still have a Student and Address class seperately but they will be mapped to only one table.

package com.vaannila.student;
 
// Generated Sep 3, 2009 6:57:20 PM by Hibernate Tools  3.2.4.GA
 
/**
 * This class contains student details.
 */
public class Student implements java.io.Serializable {
 
    private long  studentId;
    private String  studentName;
    private Address  studentAddress;
 
    public Student()  {
    }
 
    public Student(String  studentName) {
        this.studentName =  studentName;
    }
 
    public Student(String  studentName, Address studentAddress) {
        this.studentName  = studentName;
        this.studentAddress =  studentAddress;
    }
 
    public long  getStudentId() {
        return this.studentId;
    }
 
    public void  setStudentId(long  studentId) {
        this.studentId  = studentId;
    }
 
    public String  getStudentName() {
        return this.studentName;
    }
 
    public void  setStudentName(String studentName) {
        this.studentName  = studentName;
    }
 
    public Address  getStudentAddress() {
        return this.studentAddress;
    }
 
    public void  setStudentAddress(Address studentAddress) {
        this.studentAddress  = studentAddress;
    }
 
}

package com.vaannila.student;
 
// Generated Sep 3, 2009 6:57:20 PM by Hibernate Tools  3.2.4.GA
 
/**
 * This class contains student details.
 */
public class Address implements java.io.Serializable {
 
    private String  street;
    private String city;
    private String  state;
    private String zipcode;
 
    public Address()  {
    }
 
    public Address(String  street, String city, String state, String zipcode) {
        this.street  = street;
        this.city = city;
        this.state  = state;
        this.zipcode = zipcode;
    }
 
    public String  getStreet() {
        return this.street;
    }
 
    public void  setStreet(String street) {
        this.street  = street;
    }
 
    public String  getCity() {
        return this.city;
    }
 
    public void  setCity(String city) {
        this.city  = city;
    }
 
    public String  getState() {
        return this.state;
    }
 
    public void  setState(String state) {
        this.state  = state;
    }
 
    public String  getZipcode() {
        return this.zipcode;
    }
 
    public void  setZipcode(String zipcode) {
        this.zipcode  = zipcode;
    }
 
}

Create the Main class to run the example.

package com.vaannila.student;
 
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import com.vaannila.util.HibernateUtil;
 
public class Main {
 
    public static  void main(String[]  args) {
        Session session =  HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction =  session.beginTransaction();
            Address  address = new Address("OMR Road", "Chennai", "TN", "600097");
            Student  student = new Student("Eswar", address);
            session.save(student);
            transaction.commit();
        } catch  (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally  {
            session.close();
        }
 
    }
 
}

On executing the Main class you will see the following output.

Each student has one address and the values are stored in the same STUDENT table.
The folder structure of the example is shown below.

Hibernate Component Mapping

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