@Entity
public class House {
  @Id@Column(name="id")
  public long getId()

  @Basic
  public String getName()

  @OneToMany(targetEntity=Student.class,
        mappedBy="house")
  public Collection getStudentList()
}

@Entity
public class Student {
  @Id@Column(name="id")
  public long getId()

  @Basic
  public String getName()

  @ManyToOne@JoinColumn(name="house")
  public House getHouse()
}

  private void doService(PrintWriter out)
    throws java.io.IOException
  {
    Query allHouse = _entityManager.createQuery("SELECT o FROM House o");
    
    String sql = ("SELECT s" +
		  " FROM House h, IN(h.studentList) s" +
		  " WHERE h.id=?1 AND s.gender='M'");
    Query boysInHouse = _entityManager.createQuery(sql);
    
    List houses = allHouse.getResultList();

    for (int i = 0; i < houses.size(); i++) {
      House house = (House) houses.get(i);
      
      out.println("<H3>Boys living in " + house.getName() + ":</H3>");

      boysInHouse.setParameter(1, new Long(house.getId()));
      List boys = boysInHouse.getResultList();

      if (boys.size() == 0)
	out.println("No boys are living in " + house.getName());

      for (int j = 0; j < boys.size(); j++) {
	Student boy = (Student) boys.get(j);

	out.println(boy.getName() + "<br>");
      }
    }
  }
}