@OneToMany(cascade=CascadeType.ALL)

    @JoinColumn(name="fatherID") //对应儿子类的哪个字段  子类中配置ManyToOne的字段名称

    private Set<Child> children;  

@OneToMany(mappedBy = "qeTopic", cascade = CascadeType.ALL, fetch = FetchType.LAZY) //qeTopic 对应儿子类的哪个字段  子类中配置ManyToOne的字段名称

private Set<QeTopicDiscussion> listQeTopicDiscussion ;

package oneToMany;

import java.util.Set;

import javax.persistence.*;

/*

注意导入时，是导入：import javax.persistence.*;

非导入org.hibernate的相关类：import org.hibernate.annotations.Entity;

*/

@Entity

@Table(name="classes")

public class Classes implements Serializable {

  @Id

  @GeneratedValue(strategy=GenerationType.AUTO)

  private int id;

  private String name; 

  @OneToMany(cascade=CascadeType.ALL,mappedBy="classes")

  private Set<Student> students;

//getter,setter省略

} 

package oneToMany;

import javax.persistence.*;

@Entity

@Table(name="student")

public class Student implements Serializable  {

  @Id

  @GeneratedValue(strategy=GenerationType.AUTO)

  private int sid; 

  private String sname; 

  //若有多个cascade，可以是：{CascadeType.PERSIST,CascadeType.MERGE}

  @ManyToOne(cascade={CascadeType.ALL})

  @JoinColumn(name="classid")     //student类中对应外键的属性：classid

  private Classes classes;

//getter,setter省略

} 

public class TestOneToMany {

/*

CREATE TABLE    student (    --要定义外键!!!!!!!

    `sid` double NOT NULL auto_increment,

    `classid` double NULL,

    `sname` varchar(255) NOT NULL,

    PRIMARY KEY    (sid),

    INDEX par_ind (classid),

    FOREIGN KEY (classid) REFERENCES classes(id) ON DELETE CASCADE ON UPDATE CASCADE

) ENGINE=InnoDB

*/

  public static void main(String[] args) throws SQLException

  {

    try

    {

      SessionFactory sf = new AnnotationConfiguration().configure().buildSessionFactory();

      Session session=sf.openSession();

      Transaction tx=session.beginTransaction();

/*

因为mappedBy是定义在classes中,即classes类不负责维护级联关系.即维护者是student.所以,

1.要将clsses的数据,赋给student,即用student的setClasses()方法去捆定class数据;

2.在进行数据插入/更新session.save()/session.update()时,最后操作的是student.

*/

      Classes classes=new Classes();

      classes.setName("access"); 

      Student st1=new Student();

      st1.setSname("jason");

      st1.setClasses(classes);

      session.save(st1); 

      Student st2=new Student();

      st2.setSname("hwj");

      st2.setClasses(classes);

      session.save(st2);

      tx.commit();

/*

输出如下:

Hibernate: insert into classes (name) values (?)

Hibernate: insert into student (classid, sname) values (?, ?)

Hibernate: insert into student (classid, sname) values (?, ?)

*/

/*

因为一端维护关系另一端不维护关系的原因，我们必须注意避免在应用中用不维护关系的类(class)建立关系，因为这样建立的关系是不会在数据库中存储的。

如上的代码倒过来,则插入时,student的外键值为空.如下:

*/

//      Student st1=new Student();

//      st1.setSname("jason");

//      session.save(st1);

//

//      Student st2=new Student();

//      st2.setSname("hwj");

//      session.save(st2);

//

//      Set<Student> students=new HashSet<Student>();

//      students.add(st1);

//      students.add(st2);

//

//      Classes classes=new Classes();

//      classes.setName("access");

//      classes.setStudents(students);

//      session.save(classes);

/*

输出如下:

Hibernate: insert into student (classid, sname) values (?, ?)

Hibernate: insert into student (classid, sname) values (?, ?)

Hibernate: insert into classes (name) values (?)

*/

    }

    catch(HibernateException e)

    {

      e.printStackTrace();

    }

  }

}