Remove An Entity : Delete « JPA « Java

1. Java
2. JPA
3. Delete

Remove An Entity

File: Professor.java


import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Professor {
  @Id
  private int id;

  private String name;

  private long salary;

  public Professor() {
  }

  public Professor(int id) {
    this.id = id;
  }

  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 long getSalary() {
    return salary;
  }

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

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


File: ProfessorService.java

import java.util.Collection;

import javax.persistence.EntityManager;
import javax.persistence.Query;

public class ProfessorService {
  protected EntityManager em;

  public ProfessorService(EntityManager em) {
    this.em = em;
  }

  public Professor createProfessor(int id, String name, long salary) {
    Professor emp = new Professor(id);
    emp.setName(name);
    emp.setSalary(salary);
    em.persist(emp);
    return emp;
  }

  public void removeProfessor(int id) {
    Professor emp = findProfessor(id);
    if (emp != null) {
      em.remove(emp);
    }
  }

  public Professor raiseProfessorSalary(int id, long raise) {
    Professor emp = em.find(Professor.class, id);
    if (emp != null) {
      emp.setSalary(emp.getSalary() + raise);
    }
    return emp;
  }

  public Professor findProfessor(int id) {
    return em.find(Professor.class, id);
  }

  public Collection<Professor> findAllProfessors() {
    Query query = em.createQuery("SELECT e FROM Professor e");
    return (Collection<Professor>) query.getResultList();
  }
}


File: JPAUtil.java

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

public class JPAUtil {
  Statement st;
  
  public JPAUtil() throws Exception{
    Class.forName("org.hsqldb.jdbcDriver");
    System.out.println("Driver Loaded.");
    String url = "jdbc:hsqldb:data/tutorial";

    Connection conn = DriverManager.getConnection(url, "sa", "");
    System.out.println("Got Connection.");
    st = conn.createStatement();
  }
  public void executeSQLCommand(String sql) throws Exception {
    st.executeUpdate(sql);
  }
  public void checkData(String sql) throws Exception {
    ResultSet rs = st.executeQuery(sql);
    ResultSetMetaData metadata = rs.getMetaData();

    for (int i = 0; i < metadata.getColumnCount(); i++) {
      System.out.print("\t"+ metadata.getColumnLabel(i + 1)); 
    }
    System.out.println("\n----------------------------------");

    while (rs.next()) {
      for (int i = 0; i < metadata.getColumnCount(); i++) {
        Object value = rs.getObject(i + 1);
        if (value == null) {
          System.out.print("\t       ");
        } else {
          System.out.print("\t"+value.toString().trim());
        }
      }
      System.out.println("");
    }
  }
}


File: Main.java

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

public class Main {
  public static void main(String[] a) throws Exception {
    JPAUtil util = new JPAUtil();

    EntityManagerFactory emf = Persistence.createEntityManagerFactory("ProfessorService");
    EntityManager em = emf.createEntityManager();
    ProfessorService service = new ProfessorService(em);

    em.getTransaction().begin();
    Professor emp = service.createProfessor(158, "AAA", 45000);
    em.getTransaction().commit();
    System.out.println("Persisted " + emp);

    util.checkData("select * from Professor");

    // remove an employee
    em.getTransaction().begin();
    service.removeProfessor(158);
    em.getTransaction().commit();
    System.out.println("Removed Professor 158");

    util.checkData("select * from Professor");
    
    em.close();
    emf.close();
  }
}




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>

           
       

JPA-RemoveAnEmployee.zip( 5,333 k)

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