Java by API/javax.persistence/ManyToOne

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javax.persistence.ManyToOne

   <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>