Java/JPA/Many to One Mapping

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One To Many And Many To One Mapping

   <source lang="java">

File: Department.java

import java.util.HashMap; import java.util.Map; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.MapKey; import javax.persistence.OneToMany; @Entity public class Department {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   @OneToMany(mappedBy="department")
   @MapKey(name="name")
   private Map<String, Professor> employees;
   public Department() {
       employees = new HashMap<String, Professor>();
   }
   
   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 void addProfessor(Professor employee) {
       if (!getProfessors().containsKey(employee.getName())) {
           getProfessors().put(employee.getName(), employee);
           if (employee.getDepartment() != null) {
               employee.getDepartment().getProfessors().remove(employee.getName());
           }
           employee.setDepartment(this);
       }
   }
   
   public Map<String,Professor> getProfessors() {
       return employees;
   }
   public String toString() {
       return "Department id: " + getId() + 
              ", name: " + getName();
   }

}

File: Professor.java

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Professor {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   private long salary;
   
   @ManyToOne
   private Department department;
   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 Department getDepartment() {
       return department;
   }
   
   public void setDepartment(Department department) {
       this.department = department;
   }
   public String toString() {
       return "Professor id: " + getId() + " name: " + getName() + 
              " with " + getDepartment();
   }

}

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) {
   Department dept = new Department();
   dept.setName(name);
   em.persist(dept);
   return dept;
 }
 public Collection<Department> findAllDepartments() {
   Query query = em.createQuery("SELECT d FROM Department d");
   return (Collection<Department>) query.getResultList();
 }
 public Professor createProfessor(String name, long salary) {
   Professor emp = new Professor();
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public Professor setProfessorDepartment(int empId, int deptId) {
   Professor emp = em.find(Professor.class, empId);
   Department dept = em.find(Department.class, deptId);
   dept.addProfessor(emp);
   emp.setDepartment(dept);
   return emp;
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.getResultList();
 }

}

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 = service.createProfessor("empName",100L);
   Department dept = service.createDepartment("deptName");
   emp = service.setProfessorDepartment(emp.getId(),dept.getId());
   System.out.println(emp.getDepartment() + " with Professors:");
   System.out.println(emp.getDepartment().getProfessors());
   Collection<Professor> emps = service.findAllProfessors();
   if (emps.isEmpty()) {
       System.out.println("No Professors found ");
   } else {
       System.out.println("Found Professors:");
       for (Professor emp1 : emps) {
           System.out.println(emp1);
       }
   }
   Collection<Department> depts = service.findAllDepartments();
   if (depts.isEmpty()) {
       System.out.println("No Departments found ");
   } else {
       System.out.println("Found Departments:");
       for (Department dept1 : depts) {
           System.out.println(dept1 + " with " + dept1.getProfessors().size() +
                   " employees " + dept1.getProfessors());
       }
   }
   util.checkData("select * from Professor");
   util.checkData("select * from Department");
   em.getTransaction().rumit();
   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 <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>

      </source>
   
  
 
  



Persisting With Relationships Using GetReference

   <source lang="java">

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<Professor> employees;
   public Department() {
       employees = new ArrayList<Professor>();
   }
   
   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 Collection<Professor> getProfessors() {
       return employees;
   }
   public String toString() {
       return "Department no: " + getId() + 
              ", name: " + getName();
   }

}

File: Professor.java

import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Professor {

   @Id
   private int id;
   private String name;
   
   @ManyToOne
   private Department department;
   
   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 Department getDepartment() {
       return department;
   }
   
   public void setDepartment(Department dept) {
       this.department = dept;
   }
   
   public String toString() {
       return "Professor " + getId() + 
              ": name: " + getName() +
              ", dept: " + ((getDepartment() == null) ? null : getDepartment().getName());
   }

}

File: ProfessorService.java import java.util.Collection; import javax.persistence.EntityManager; public class ProfessorService {

 protected EntityManager em;
 public ProfessorService(EntityManager em) {
   this.em = em;
 }
 public Professor createProfessor(int empId, String empName, int deptId) {
   Department dept = em.getReference(Department.class, deptId);
   Professor emp = new Professor();
   emp.setId(empId);
   emp.setName(empName);
   emp.setDepartment(dept);
   dept.getProfessors().add(emp);
   em.persist(emp);
   return emp;
 }
 public Collection<Professor> findAllProfessors() {
   return (Collection<Professor>) em.createQuery("SELECT e FROM Professor e").getResultList();
 }
 public Collection<Department> findAllDepartments() {
   return (Collection<Department>) em.createQuery("SELECT d FROM Department d").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 java.util.Iterator; 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();
   service.createProfessor(1, "empName", 1);
   util.checkData("select * from Professor");
   em.getTransaction().rumit();
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>

      </source>
   
  
 
  



Use One Joined Column

   <source lang="java">


File: Department.java

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; @Entity public class Department {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   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 String toString() {
       return "Department id: " + getId() + 
              ", name: " + getName();
   }

}

File: Professor.java

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; @Entity public class Professor {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   private long salary;
   
   @ManyToOne
   @JoinColumn(name="DEPT_ID")
   private Department department;
   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 Department getDepartment() {
       return department;
   }
   
   public void setDepartment(Department department) {
       this.department = department;
   }
   public String toString() {
       return "Professor id: " + getId() + " name: " + getName() + 
              " with " + getDepartment();
   }

}

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(String name, long salary) {
   Professor emp = new Professor();
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public Professor setProfessorDepartment(int empId, int deptId) {
   Professor emp = em.find(Professor.class, empId);
   Department dept = em.find(Department.class, deptId);
   emp.setDepartment(dept);
   return emp;
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.getResultList();
 }
 public Department createDepartment(String name) {
   Department dept = new Department();
   dept.setName(name);
   em.persist(dept);
   return dept;
 }
 public Collection<Department> findAllDepartments() {
   Query query = em.createQuery("SELECT d FROM Department d");
   return (Collection<Department>) 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 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 = service.createProfessor("empName", 100);
   
   
   
   Department dept = service.createDepartment("deptName");
   
   
   
   service.setProfessorDepartment(emp.getId(), dept.getId());
   
   Collection<Professor> emps = service.findAllProfessors();
   for (Professor emp1 : emps) {
     System.out.println(emp1);
   }
   Collection<Department> depts = service.findAllDepartments();
   for (Department dept1 : depts) {
     System.out.println(dept1);
   }
   util.checkData("select * from Professor");
   util.checkData("select * from Department");
   em.getTransaction().rumit();
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>

      </source>
   
  
 
  



Use Two Joined Columns for Many to one Mapping

   <source lang="java">

File: Professor.java

import java.util.ArrayList; import java.util.Collection; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.IdClass; import javax.persistence.JoinColumn; import javax.persistence.JoinColumns; import javax.persistence.JoinTable; import javax.persistence.ManyToMany; import javax.persistence.ManyToOne; import javax.persistence.OneToMany; @Entity @IdClass(ProfessorId.class) public class Professor {

   @Id private String country;
   @Id
   @Column(name="EMP_ID")
   private int id;
   private String name;
   private long salary;
   @ManyToOne 
   @JoinColumns({
       @JoinColumn(name="MGR_COUNTRY", referencedColumnName="COUNTRY"),
       @JoinColumn(name="MGR_ID", referencedColumnName="EMP_ID")
   })
   private Professor manager;
   @OneToMany(mappedBy="manager")
   private Collection<Professor> directs;
   @ManyToMany 
   @JoinTable(
       name="EMP_PROJECT", 
       joinColumns={
           @JoinColumn(name="EMP_COUNTRY", referencedColumnName="COUNTRY"),
           @JoinColumn(name="EMP_ID", referencedColumnName="EMP_ID")},
       inverseJoinColumns=@JoinColumn(name="PROJECT_ID"))
   private Collection<Project> projects;
   public Professor() {
       directs = new ArrayList<Professor>();
       projects = new ArrayList<Project>();
   }
   
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   public String getCountry() {
       return country;
   }
   public void setCountry(String country) {
       this.country = country;
   }
   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 Collection<Professor> getDirects() {
       return directs;
   }
   
   public Professor getManager() {
       return manager;
   }
   
   public void setManager(Professor manager) {
       this.manager = manager;
   }
   
   public Collection<Project> getProjects() {
       return projects;
   }
   public String toString() {
       return "Professor id: " + getId() + " name: " + getName() +
              " country: " + getCountry();
   }

}

File: ProfessorId.java import java.io.Serializable; import javax.persistence.Column; import javax.persistence.Embeddable; @Embeddable public class ProfessorId implements Serializable{

 private String country;
 @Column(name = "EMP_ID")
 private int id;
 public ProfessorId() {
 }
 public ProfessorId(String country, int id) {
   this.country = country;
   this.id = id;
 }
 public String getCountry() {
   return country;
 }
 public int getId() {
   return id;
 }
 public boolean equals(Object o) {
   return ((o instanceof ProfessorId) && country.equals(((ProfessorId) o).getCountry()) && id == ((ProfessorId) o)
       .getId());
 }
 public int hashCode() {
   return country.hashCode() + id;
 }

}

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(String country, int id, String name, long salary) {
   Professor emp = new Professor();
   emp.setCountry(country);
   emp.setId(id);
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public void createProject(String projName) {
   Project proj = new Project();
   proj.setName(projName);
   em.persist(proj);
 }
 public void setProfessorManager(String country, int id, String mgrCountry, int mgrId) {
   Professor emp = findProfessor(country, id);
   Professor mgr = findProfessor(mgrCountry, mgrId);
   emp.setManager(mgr);
   mgr.getDirects().add(emp);
 }
 public void addProfessorProject(String country, int id, int projId) {
   Professor emp = findProfessor(country, id);
   Project proj = em.find(Project.class, projId);
   emp.getProjects().add(proj);
   proj.getProfessors().add(emp);
 }
 public Professor findProfessor(String country, int id) {
   return em.find(Professor.class, new ProfessorId(country, id));
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.getResultList();
 }
 public Collection<Project> findAllProjects() {
   Query query = em.createQuery("SELECT p FROM Project p");
   return (Collection<Project>) query.getResultList();
 }

}

File: Project.java import java.util.ArrayList; import java.util.Collection; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.ManyToMany; @Entity public class Project {

 @Id
 protected int id;
 protected String name;
 @ManyToMany(mappedBy = "projects")
 protected Collection<Professor> employees = new ArrayList<Professor>();
 public int getId() {
   return id;
 }
 public void setId(int projectNo) {
   this.id = projectNo;
 }
 public String getName() {
   return name;
 }
 public void setName(String projectName) {
   this.name = projectName;
 }
 public Collection<Professor> getProfessors() {
   return employees;
 }
 public void addProfessor(Professor employee) {
   if (!getProfessors().contains(employee)) {
     getProfessors().add(employee);
   }
   if (!employee.getProjects().contains(this)) {
     employee.getProjects().add(this);
   }
 }
 public String toString() {
   return getClass().getName().substring(getClass().getName().lastIndexOf(".") + 1) + " no: "
       + getId() + ", name: " + getName();
 }

}

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();
   service.createProfessor("country", 1, "name", 100);
   service.createProfessor("mgrcountry", 2, "mgrName", 100);
   service.createProject("proj");
   service.addProfessorProject("empCountry2", 1, 1);
   service.setProfessorManager("Country", 1, "mgrCountry", 1);
   System.out.println("Professors:");
   for (Professor emp : service.findAllProfessors()) {
     System.out.println(emp + " " + emp.getProjects().size());
     System.out.println(emp + " " + emp.getManager());
   }
   System.out.println("Projects:");
   for (Project p : service.findAllProjects()) {
     System.out.print(p + " " + p.getProfessors().size());
   }
   util.checkData("select * from Professor");
   em.getTransaction().rumit();
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>

      </source>