Mark Discriminator Column For Entities In Hierarchy : Inheritance « JPA « Java Tutorial






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>
  Download:  JPA-MarkDiscriminatorColumnForEntitiesInHierarchy.zip( 5,291 k)








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