Many to One Map With Entity Hierarchy : Many to One Mapping « JPA « Java Tutorial

1. Java Tutorial
2. JPA
3. Many to One Mapping

File: Employee.java

import java.util.Date;

import javax.persistence.AssociationOverride;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.MappedSuperclass;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Employee {
  @Id
  private int id;

  private String name;

  @Temporal(TemporalType.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 CompanyEmployee extends Employee {
  private int vacation;

  @ManyToOne
  private Employee manager;

  public int getVacation() {
    return vacation;
  }

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

  public Employee getManager() {
    return manager;
  }

  public void setManager(Employee manager) {
    this.manager = manager;
  }
}

@Entity
@AssociationOverride(name = "manager", joinColumns = @JoinColumn(name = "MGR"))
class PartTimeEmployee extends CompanyEmployee {

  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();
  }
}

@Entity
class FullTimeEmployee extends CompanyEmployee {
  private long salary;


  private long pensionContribution;

  public long getPensionContribution() {
    return pensionContribution;
  }

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

  public long getSalary() {
    return salary;
  }

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

  public String toString() {
    return "FullTimeEmployee 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);
    emp1.setVacation(1);
    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>

22.11.Many to One Mapping
	22.11.1.	Mapping Relationship State
	22.11.2.	Many To One Set Join Column Name
	22.11.3.	Many to One Map With Entity Hierarchy
	22.11.4.	Many To One Mapping Unique Join Column
	22.11.5.	Many To One Mapping Manually Linking
	22.11.6.	Many To One Insertable Nullable Updatable
	22.11.7.	Many To One Cascasde Persist
	22.11.8.	Many To One Cascade Remove
	22.11.9.	Many To One Cascade Merge