单向一对多的关联映射

1、学生表student 和年级表 grade

2、类Student 和Grade类

Student:

1 public class Student {
2     private int id;
3     private String name;
4     private int age;
5 //get…set
6 }

Grade:

1 public class Grade {
2     private int id;
3     private String name;
4     private Set<Student> students = new HashSet<Student>(0);    //get…set
5 }

3、映射文件

Grade.hbm.xml

 1 <hibernate-mapping package="cn.siggy.pojo">
 2     <class name="Grade">
 3         <id name="id">
 4             <generator class="native"></generator>
 5         </id>
 6         <property name="name"/>
 7         <!-- set是 Grade中的集合属性  name属性名称 -->
 8         <set name="students">
 9             <!-- key表示外键  column外键列名-->
10             <key column="grade_id" not-null="true"></key>
11             <!-- one-to-many 一对多  类Grade 中  students 所表示类型 -->
12             <one-to-many class="Student"/>
13         </set>
14     </class>
15 </hibernate-mapping>

Student.hbm.xml

 1 <hibernate-mapping package="cn.siggy.pojo">
 2     <class name="Student">
 3         <id name="id">
 4             <generator class="native"></generator>
 5         </id>
 6         <property name="name"/>
 7         <property name="age"/>
 8     
 9 　　</class>
10 </hibernate-mapping>

4、测试代码

 1 @Test
 2     public void testSave() throws HibernateException, SerialException, SQLException{
 3         Session session = null;
 4         Transaction tx = null;
 5         try{
 6             session = HibernateUtil.getSession();
 7             tx = session.beginTransaction();
 8             Grade grade = new Grade();
 9             grade.setName("基础");
10             
11             Student stu = new Student();
12             stu.setName("张三疯");
13             stu.setAge(22);
14             Student stu1 = new Student();
15             stu1.setName("老王");
16             stu1.setAge(23);
17             //关联
18             grade.getStudents().add(stu);
19             grade.getStudents().add(stu1);
20             //保存数据的顺序 是根据外键的配置来决定的
21             //如果外键不能为null,那么先保存一的一端
22             //如果外键可以为null,则可以随意保存
23             session.save(grade);
24             session.save(stu);
25             session.save(stu1);
26             
27             tx.commit();
28             
29         }catch (HibernateException e) {
30             if(tx!=null)
31                 tx.rollback();
32             e.printStackTrace();
33             throw e;
34         }finally{
35             HibernateUtil.closeSession();
36         }
37     }
38     @Test
39     public void testGet(){
40         Session session = null;
41         Transaction tx = null;
42         try{
43             session = HibernateUtil.getSession();
44             tx = session.beginTransaction();
45             //取数据
46             Grade grade = (Grade)session.get(Grade.class, 1);
47             System.out.println("gradeName="+grade.getName());
48             System.out.println("grade所对应的多的一端的数据");
49             Iterator<Student> iter = grade.getStudents().iterator();
50             for(;iter.hasNext();){
51                 Student temp = iter.next();
52                 System.out.println("name="+temp.getName()+"	age="+temp.getAge());
53             }
54             tx.commit();
55         }catch (HibernateException e) {
56             if(tx!=null)
57                 tx.rollback();
58             e.printStackTrace();
59             throw e;
60         }finally{
61             HibernateUtil.closeSession();
62         }
63     }