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();
em.getTransaction().commit();
em.close();
emf.close();
Helper.checkData();
}
}
File: Project.java
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
@Entity
@IdClass(ProjectId.class)
public class Project {
@Id
@Column(name="Student_ID", insertable=false, updatable=false)
private int studentId;
@Id private String name;
@ManyToOne
@JoinColumn(name="Student_ID")
private Student student;
@Temporal(TemporalType.DATE)
@Column(name="START_DATE")
private Date startDate;
@Temporal(TemporalType.DATE)
@Column(name="END_DATE")
private Date endDate;
public Project() {}
public Project(Student student) {
this.student = student;
this.studentId = student.getId();
}
public String getName() {
return name;
}
public void setName(String projectName) {
this.name = projectName;
}
public int getDeptId() {
return studentId;
}
public Student getStudent() {
return student;
}
public Date getEndDate() {
return endDate;
}
public void setEndDate(Date endDate) {
this.endDate = endDate;
}
public Date getStartDate() {
return startDate;
}
public void setStartDate(Date startDate) {
this.startDate = startDate;
}
public String toString() {
return "Project name: " + getName();
}
}
File: ProjectId.java
import java.io.Serializable;
public class ProjectId implements Serializable {
private int studentId;
private String name;
public ProjectId() {}
public ProjectId(int deptId, String name) {
this.studentId = deptId;
this.name = name;
}
public String getName() {
return name;
}
public int getId() {
return studentId;
}
public boolean equals(Object o) {
return ((o instanceof ProjectId) &&
name.equals(((ProjectId) o).getName()) &&
studentId == ((ProjectId) o).getId());
}
public int hashCode() {
return name.hashCode() + studentId;
}
}
File: Student.java
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Student {
@Id
private int id;
private String name;
@OneToMany(mappedBy="student")
private Collection<Project> projects;
public Student() {
projects = new ArrayList<Project>();
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String deptName) {
this.name = deptName;
}
public Collection<Project> getProjects() {
return projects;
}
public String toString() {
return "Student 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: 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-IDEntityWithHashCodeAndEquals.zip( 5,290 k)