Three Leve Entity Hierarchy : Inheritance « JPA « Java Tutorial

1. Java Tutorial
2. JPA
3. Inheritance

File: Employee.java

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.MappedSuperclass;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
@Table(name = "EMP")
@Inheritance
@DiscriminatorColumn(name = "EMP_TYPE")
public abstract class Employee {
  @Id
  private int id;

  private String name;

  @Temporal(TemporalType.DATE)
  @Column(name = "S_DATE")
  private Date startDate;

  public int getId() {
    return id;
  }

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

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public Date getStartDate() {
    return startDate;
  }

  public void setStartDate(Date startDate) {
    this.startDate = startDate;
  }

  public String toString() {
    return "Employee id: " + getId() + " name: " + getName();
  }
}

@MappedSuperclass
abstract class AbstractEmployee extends Employee {
  private int vacation;

  public int getVacation() {
    return vacation;
  }

  public void setVacation(int vacation) {
    this.vacation = vacation;
  }
}

@Entity
@DiscriminatorValue("FTEmp")
class FullTimeEmployee extends AbstractEmployee {
  private long salary;

  private long pension;

  public long getPension() {
    return pension;
  }

  public void setPension(long pension) {
    this.pension = pension;
  }

  public long getSalary() {
    return salary;
  }

  public void setSalary(long salary) {
    this.salary = salary;
  }

  public String toString() {
    return "FullTimeEmployee id: " + getId() + " name: " + getName();
  }
}

@Entity(name = "PTEmp")
@DiscriminatorValue("PTEmp")
class PartTimeEmployee extends AbstractEmployee {
  @Column(name = "H_RATE")
  private float hourlyRate;

  public float getHourlyRate() {
    return hourlyRate;
  }

  public void setHourlyRate(float hourlyRate) {
    this.hourlyRate = hourlyRate;
  }

  public String toString() {
    return "PartTimeEmployee id: " + getId() + " name: " + getName();
  }
}

File: Helper.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class Helper {
  public static void checkData() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    Connection conn = DriverManager.getConnection("jdbc:hsqldb:data/tutorial", "sa", "");
    Statement st = conn.createStatement();

    ResultSet mrs = conn.getMetaData().getTables(null, null, null, new String[] { "TABLE" });
    while (mrs.next()) {
      String tableName = mrs.getString(3);
      System.out.println("\n\n\n\nTable Name: "+ tableName);

      ResultSet rs = st.executeQuery("select * from " + tableName);
      ResultSetMetaData metadata = rs.getMetaData();
      while (rs.next()) {
        System.out.println(" Row:");
        for (int i = 0; i < metadata.getColumnCount(); i++) {
          System.out.println("    Column Name: "+ metadata.getColumnLabel(i + 1)+ ",  ");
          System.out.println("    Column Type: "+ metadata.getColumnTypeName(i + 1)+ ":  ");
          Object value = rs.getObject(i + 1);
          System.out.println("    Column Value: "+value+"\n");
        }
      }
    }
  }
}

File: Main.java

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

public class Main {
  static EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAService");

  static EntityManager em = emf.createEntityManager();

  public static void main(String[] a) throws Exception {
    em.getTransaction().begin();

    PartTimeEmployee emp = new PartTimeEmployee();
    emp.setId(1);
    emp.setName("Tom");
    emp.setStartDate(new java.util.Date());
    emp.setHourlyRate(12);
    em.persist(emp);
    
    FullTimeEmployee emp1 = new FullTimeEmployee();
    emp1.setId(2);
    emp1.setName("Tom");
    emp1.setStartDate(new java.util.Date());
    emp1.setSalary(123);
    
    em.persist(emp1);


    em.getTransaction().commit();
    em.close();
    emf.close();

    Helper.checkData();
  }
}

File: persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
  <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
      <property name="hibernate.connection.username" value="sa"/>
      <property name="hibernate.connection.password" value=""/>
      <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
  </persistence-unit>
</persistence>

22.16.Inheritance
	22.16.1.	Persist subclass
	22.16.2.	Three Leve Entity Hierarchy
	22.16.3.	Set Discriminator Value In Subclass
	22.16.4.	Mark Discriminator Column For Entities In Hierarchy
	22.16.5.	Mark Abstract Entity With Inheritance
	22.16.6.	Inheritance Type TABLE_PER_CLASS
	22.16.7.	Inheritance Type JOINED
	22.16.8.	Discriminator Type: INTEGER
	22.16.9.	Discriminator Column And Discriminator Value
	22.16.10.	Change Inheritance Type
	22.16.11.	Add Properties In Abstract Entity
	22.16.12.	Adding Properties To SubClasses
	22.16.13.	Abstract Class As Mapped Superclass