hibernate table per class hierarchy XML- mapping

Problem of Inheritance:

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in the relational environment does not directly support inheritance, however, we can consider the following three  choices.

1.    Table per class hierarchy

2.     Table for subclass.

3.     Table for concrete class.

Table per class hierarchy:

                  In this process we can map the entire class hierarchy to a single table. This table includes columns ofr the properties of al classes in the hierarchy.

Benefits :

              This is basic and easier to use, and efficient to  compare other two approaches.

Problems:

               The columns for properties declared by subclasses must be declared to accept null

Values, these columns cannot be declared with NOT NULL constraint.

Database:

create table employeedetails(empno int(4),category char(16),ename char(16),annualSal int(4))

Ex3:

//this program will describes – Table per class hierarchy

Employee.java

package madhav;

public class Employee {

       private int empno;

       private String ename;

       public int getEmpno() {

             return empno;

       }

       public void setEmpno(int empno) {

             this.empno = empno;

       }

       public String getEname() {

             return ename;

       }

       public void setEname(String ename) {

             this.ename = ename;

       }

}

SalariedEmployee.java

package madhav;

public class SalariedEmployee extends Employee{

      public double annualSal;

    public double getAnnualSal() {

          return annualSal;

    }

    public void setAnnualSal(double annualSal) {

          this.annualSal = annualSal;

    }

    public String toString()

    {

      return "salariedEmployee";

    }

}

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>

  <class name="madhav.Employee" table="employeedetails">

   <id name="empno" type="int" column="empno" >

   <generator class="increment"/>

  </id>

<discriminator column="category"></discriminator>

  <property name="ename">

   <column name="ename" />

  </property>

  <subclass name="madhav.SalariedEmployee" discriminator-value="salaried">

  <property name="annualSal"></property>

  </subclass>

 </class>

</hibernate-mapping>

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">

<!-- Generated by MyEclipse Hibernate Tools.                   -->

<hibernate-configuration>

    <session-factory>

        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <property name="connection.url">jdbc:mysql://localhost:3306/mysql</property>

        <property name="connection.username">madhav</property>

        <property name="connection.password">madhav</property>

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>

        <property name="hbm2ddl.auto">create</property>

    <mapping resource="employee.hbm.xml"/>

    </session-factory>

</hibernate-configuration>

                                                                                

                                                                       

TestCase.java

package madhav;

import org.hibernate.SessionFactory;

import org.hibernate.classic.Session;

import org.hibernate.cfg.*;

import org.hibernate.*;

import org.apache.log4j.*;

public class TestCase {

     /**

      * @param args

      */

     SessionFactory factory;

   

     public void createEmp(SalariedEmployee sm)

     {

      Session session=null;

      Transaction tx=null;

      try

      {

                 

                  session =factory.openSession();

                 

                 

tx=session.beginTransaction();

                 

                  System.out.println("break1 in cd");

                  session.save(sm);

                 

                  tx.commit();

                  System.out.println("record inserted");

      }

      catch(HibernateException e)

      {

               

     e.printStackTrace();

                 

      }

     }

     public static void main(String[] args) {

                 // TODO Auto-generated method stub

      System.out.println("first");

                 TestCase t=new TestCase();

                 Configuration cfg=new Configuration();

                 cfg.configure();

                 //cfg.addResource("employee.hbm.xml");

                 //cfg.addResource("personaldetails.hbm.xml");

                 System.out.println("break 2");

               

t.factory=cfg.buildSessionFactory();

                 SalariedEmployee se=new SalariedEmployee();

                 se.setEname("madhav");

                 se.setAnnualSal(9600);

                 t.createEmp(se);

System.out.println("execution over");

     }

}

Output –console:

Output-sql-prompt:

Related Topics:

1. hibernate-basic-example(xml-based)
2. hibernate-inheritance-tableforclass-hierarchy(xml-based)
3. hibernate-inheritance-joinsubclass-(xml-based)
4. hibernate-inheritance-tableforconcreteclass(xml-based)
5. hibernate-onetoone-relation(xml-based)
6. hibernate-onetomany-relation(xml-based)
7. hibernate-manytomany-relation(xml-based)
8. hibernate-basic-example(Annotation-based)
9. hibernate-inheritance-tableforclass-hierarchy(Annotation-based)
10. hibernate-inberitance-joinsubclass-(Annotation-based)
11. hibernate-inheritance-tableforconcreteclass(Annotation-based)
12. hibernate-onetoone-relation(Annotation-based)
13. hibernate-onetomany-relation(Annotation-based)
14. hibernate-manytomany-relation(Annotation-based)