File: Department.java
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Department {
@Id
private int id;
private String name;
@OneToMany(mappedBy="department")
private Collection projects;
public Department() {
projects = new ArrayList();
}
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 getProjects() {
return projects;
}
public String toString() {
return "Department id: " + getId() +
", name: " + getName();
}
}
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 Department createDepartment(String name, int id) {
Department dept = new Department();
dept.setId(id);
dept.setName(name);
em.persist(dept);
return dept;
}
public Project createProject(String name, int deptId) {
Project proj = new Project(findDepartment(deptId));
proj.setName(name);
em.persist(proj);
return proj;
}
public Department findDepartment(int id) {
return em.find(Department.class, id);
}
public Collection findAllProjects() {
Query query = em.createQuery("SELECT p FROM Project p");
return (Collection) query.getResultList();
}
public Collection findAllDepartments() {
Query query = em.createQuery("SELECT d FROM Department d");
return (Collection) query.getResultList();
}
}
File: Project.java
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
@Entity
@IdClass(ProjectId.class)
public class Project {
@Id
@Column(name = "DEPT_ID", insertable = false, updatable = false)
private int deptId;
@Id
private String name;
@ManyToOne
@JoinColumn(name = "DEPT_ID")
private Department department;
public Project() {
}
public Project(Department dept) {
this.department = dept;
this.deptId = dept.getId();
}
public String getName() {
return name;
}
public void setName(String projectName) {
this.name = projectName;
}
public int getDeptId() {
return deptId;
}
public Department getDepartment() {
return department;
}
public String toString() {
return "Project name: " + getName();
}
}
File: ProjectId.java
import java.io.Serializable;
public class ProjectId implements Serializable {
private int deptId;
private String name;
public ProjectId() {}
public ProjectId(int deptId, String name) {
this.deptId = deptId;
this.name = name;
}
public String getName() {
return name;
}
public int getId() {
return deptId;
}
public boolean equals(Object o) {
return ((o instanceof ProjectId) &&
name.equals(((ProjectId) o).getName()) &&
deptId == ((ProjectId) o).getId());
}
public int hashCode() {
return name.hashCode() + deptId;
}
}
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();
Department dept = service.createDepartment("name",1);
System.out.print("Created" + dept);
Project proj = service.createProject("name", 1);
System.out.print("Created" + proj);
System.out.println("Project:");
for (Project p : service.findAllProjects()) {
System.out.println(p + " " + p.getDepartment());
}
System.out.println("Departments:");
for (Department d : service.findAllDepartments()) {
System.out.println(d + " " + d.getProjects().size());
}
util.checkData("select * from Project");
em.getTransaction().commit();
em.close();
emf.close();
}
}
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: persistence.xml
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
JPA-RelationshipOnId.zip( 5,336 k)