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("\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 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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JPA-MergingDetachedEntities.zip( 5,333 k)