Java/JPA/One to Many Mapping

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One To Many based on List Collection

   <source lang="java">

File: Department.java

import java.util.ArrayList; import java.util.Collection; import java.util.List; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; import javax.persistence.OrderBy; @Entity public class Department { 

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 private int id;
 private String name;
 @OneToMany(mappedBy = "department")
 @OrderBy("name ASC")
 private List<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 deptName) {
   this.name = deptName;
 }
 public void addProfessor(Professor employee) {
   if (!getProfessors().contains(employee)) {
     getProfessors().add(employee);
     if (employee.getDepartment() != null) {
       employee.getDepartment().getProfessors().remove(employee);
     }
     employee.setDepartment(this);
   }
 }
 public Collection<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);
   return emp;

} public Collection<Professor> findAllProfessors() { 

   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) 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", 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: 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>



One To Many Bidirectional Mapping

   <source lang="java">

File: Department.java

import java.util.ArrayList; import java.util.Collection; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; @Entity public class Department { 

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   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 deptName) {
       this.name = deptName;
   }
   
   public void addProfessor(Professor employee) {
       if (!getProfessors().contains(employee)) {
           getProfessors().add(employee);
           if (employee.getDepartment() != null) {
               employee.getDepartment().getProfessors().remove(employee);
           }
           employee.setDepartment(this);
       }
   }
   
   public Collection<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);
   return emp;
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) 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");
   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");
       }
   }

   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>



One To Many MappedBy

   <source lang="java">

File: Department.java

import java.util.ArrayList; import java.util.Collection; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; @Entity public class Department { 

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   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 deptName) {
       this.name = deptName;
   }
   
   public void addProfessor(Professor employee) {
       if (!getProfessors().contains(employee)) {
           getProfessors().add(employee);
           if (employee.getDepartment() != null) {
               employee.getDepartment().getProfessors().remove(employee);
           }
           employee.setDepartment(this);
       }
   }
   
   public Collection<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);
   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",100);
   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");
       }
   }

   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>



One To Many Mapping with generated primary key

   <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.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 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");
   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>



One To Many Mapping With MappedBy: To remove Mapping Table

   <source lang="java">

File: Student.java import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Student { 

 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id;
 private String name;
 @ManyToOne (cascade=CascadeType.ALL)
 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 department) {
   this.department = department;
 }
 public String toString() {
   return "\n\nID:" + id + "\nName:" + name + "\n\n" + department;
 }

}

File: Department.java

import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; @Entity public class Department { 

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   @OneToMany(mappedBy="department",cascade=CascadeType.ALL)
   private Set<Student> students;
   
   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 Set<Student> getStudents() {
     return students;
   }
   public void setStudent(Set<Student> students) {
     this.students = students;
   }
   public String toString() {
       return "Department id: " + getId() + 
              ", name: " + getName()+"Student:"+ students;
   }

}

File: Main.java import java.util.List; 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();
   
   
   Student student = new Student();
   student.setName("Joe");
   em.persist(student);
   
   Student student1 = new Student();
   student1.setName("Joe");
   em.persist(student1);
   
   Department dept = new Department();
   dept.setName("dept name");
   student.setDepartment(dept);
   student1.setDepartment(dept);
   
   em.flush();
   




   Query query = em.createQuery("SELECT e FROM Student e");
   List<Student> list = (List<Student>) query.getResultList();
   System.out.println(list.get(0).getDepartment());
   
   query = em.createQuery("SELECT d FROM Department d");
   List<Department> dList = (List<Department>) query.getResultList();
   System.out.println(dList.get(0).getStudents());
   
   em.getTransaction().rumit();
   em.close();
   emf.close();
   
   Helper.checkData();
 }

}

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.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>



One To Many Target Entity

   <source lang="java">

File: Department.java

import java.util.ArrayList; import java.util.Collection; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; @Entity public class Department { 

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   @OneToMany(targetEntity=Professor.class, mappedBy="department")
   private Collection 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 deptName) {
       this.name = deptName;
   }
   
   public void addProfessor(Professor employee) {
       if (!getProfessors().contains(employee)) {
           getProfessors().add(employee);
           if (employee.getDepartment() != null) {
               employee.getDepartment().getProfessors().remove(employee);
           }
           employee.setDepartment(this);
       }
   }
   
   public Collection 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);
   return emp;
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) 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");
   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");
       }
   }

   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>



One To Many Unidirectional Mapping

   <source lang="java">

File: Phone.java

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

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 private int id;
 @Column(name = "NUM")
 private String number;
 private String type;
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 public String getNumber() {
   return number;
 }
 public void setNumber(String phoneNo) {
   this.number = phoneNo;
 }
 public String getType() {
   return type;
 }
 public void setType(String phoneType) {
   this.type = phoneType;
 }
 public String toString() {
   return "Phone id: " + getId() + ", no: " + getNumber() + ", type: " + getType();
 }

}

File: Professor.java

import java.util.ArrayList; import java.util.Collection; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.JoinTable; import javax.persistence.OneToMany; @Entity public class Professor { 

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 private int id;
 private String name;
 private long salary;
 @OneToMany
 @JoinTable(name = "EMP_PHONE", joinColumns = @JoinColumn(name = "EMP_ID"), inverseJoinColumns = @JoinColumn(name = "PHONE_ID"))
 private Collection<Phone> phones;
 public Professor() {
   phones = new ArrayList<Phone>();
 }
 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 void addPhone(Phone phone) {
   if (!getPhones().contains(phone)) {
     getPhones().add(phone);
   }
 }
 public Collection<Phone> getPhones() {
   return phones;
 }
 public String toString() {
   return "Professor id: " + getId() + " name: " + getName() + " with " + getPhones().size()
       + " phones";
 }

}

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 addProfessorPhone(int empId, int phoneId) {
   Professor emp = em.find(Professor.class, empId);
   Phone phone = em.find(Phone.class, phoneId);
   emp.addPhone(phone);
   return emp;
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.getResultList();
 }
 public Phone createPhone(String num, String type) {
   Phone phone = new Phone();
   phone.setNumber(num);
   phone.setType(type);
   em.persist(phone);
   return phone;
 }
 public Collection<Phone> findAllPhones() {
   Query query = em.createQuery("SELECT p FROM Phone p");
   return (Collection<Phone>) 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);
   
   Phone phone = service.createPhone("1111111111","phoneType");
   emp = service.addProfessorPhone(emp.getId(),phone.getId());
   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<Phone> phones = service.findAllPhones();
   if (phones.isEmpty()) {
       System.out.println("No Phones found ");
   } else {
     System.out.println("Found Phones:");
       for (Phone phone1 : phones) {
         System.out.println(phone1);
       }
   }

   util.checkData("select * from Professor");
   
   util.checkData("select * from Phone");
   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>



Query for One To Many Mapping

   <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;
   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 long getSalary() {
       return salary;
   }
   public Department getDepartment() {
       return department;
   }
   public void setDepartment(Department dept) {
       this.department = dept;
   }
   
   public String toString() {
       return "Professor " + getId() + 
              ": name: " + getName() +
              ", salary: " + getSalary();
   }

}

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

 protected EntityManager em;
 public ProfessorService(EntityManager em) {
   this.em = em;
 }
 public List findAll() {
   return 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();
   service.findAll();
   
   
   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 Collection In One To Many Mapping

   <source lang="java">

File: Department.java

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

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   @OneToMany(mappedBy="department")
   private Collection<Student> students;
   
   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<Student> getStudents() {
     return students;
   }
   public void setStudent(Collection<Student> students) {
     this.students = students;
   }
   public String toString() {
       return "Department id: " + getId() + 
              ", name: " + getName();
   }

}

File: Student.java import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Student { 

 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id;
 private String name;
 @ManyToOne (cascade=CascadeType.ALL)
 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 department) {
   this.department = department;
 }
 public String toString() {
   return "\n\nID:" + id + "\nName:" + name + "\n\n" + department;
 }

}

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: Main.java import java.util.List; 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();
   
   
   Student student = new Student();
   student.setName("Joe");
   em.persist(student);
   
   Student student1 = new Student();
   student1.setName("Joe");
   em.persist(student1);
   
   Department dept = new Department();
   dept.setName("dept name");
   student.setDepartment(dept);
   student1.setDepartment(dept);
   
   em.flush();
   




   Query query = em.createQuery("SELECT e FROM Student e");
   List<Student> list = (List<Student>) query.getResultList();
   System.out.println(list);
   
   query = em.createQuery("SELECT d FROM Department d");
   List<Department> dList = (List<Department>) query.getResultList();
   System.out.println(dList);
   
   em.getTransaction().rumit();
   em.close();
   emf.close();
   
   Helper.checkData();
 }

}


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>
Источник — «http://jexp.ru/index.php?title=Java/JPA/One_to_Many_Mapping&oldid=8957»