Source Code : Merging Detached Entities

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Merging Detached Entities

File: Professor.java


import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
public class Professor {
    @Id
    private int id;
    private String name;
    
    @Temporal(TemporalType.TIMESTAMP)
    private Date lastAccessTime;
    

    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 getLastAccessTime() {
        return lastAccessTime;
    }
    
    public void setLastAccessTime(Date lastAccessTime) {
        this.lastAccessTime = lastAccessTime;
    }
    
    public String toString() {
        return "Professor " + getId() + 
               ": name: " + getName() +
               " lastAccessTime: " + getLastAccessTime();
    }
}


File: ProfessorService.java

import java.util.Collection;
import java.util.Date;

import javax.persistence.EntityManager;

public class ProfessorService {
  protected EntityManager em;

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

  public void updateProfessor(Professor emp) {
    if (em.find(Professor.class, emp.getId()) == null) {
      throw new IllegalArgumentException("Unknown employee id: " + emp.getId());
    }
    Professor managedEmp = em.merge(emp);
    managedEmp.setLastAccessTime(new Date());
  }

  public void updateProfessorIncorrect(Professor emp) {
    if (em.find(Professor.class, emp.getId()) == null) {
      throw new IllegalArgumentException("Unknown employee id: " + emp.getId());
    }
    em.merge(emp);
    emp.setLastAccessTime(new Date());
  }

  public Collection<Professor> findAllProfessors() {
    return (Collection<Professor>) em.createQuery("SELECT e FROM Professor e").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("	"+ metadata.getColumnLabel(i + 1)); 
    }
    System.out.println("
----------------------------------");

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


File: Main.java

import java.util.Collection;

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 = new Professor();
    emp.setId(1);
    emp.setName("name");
    service.updateProfessor(emp);

    emp = new Professor();
    emp.setId(1);
    emp.setName("name");
    service.updateProfessorIncorrect(emp);
    
    util.checkData("select * from Professor");
    util.checkData("select * from Address");

    
    em.getTransaction().commit();
    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>



           
       

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