hibernate 之 关联映射的单向一对多关联

1. 老是和学生之间一对多关系，一个老是对应多个学生。一对多的表结构和多对一的表结构一样。

表结构如下：

2. 类结构：Teacher.java:

public class Teacher {
    private int id;
    private String name;
    private Set<Student> students;
    public Teacher() {
    }
    public Teacher(String name) {
        super();
        this.name = name;
    }

    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 Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}

Student.java:

public class Student {
    private int id;
    private String name;
    private String sex;
    public Student() {
    }
    public Student(String name, String sex) {
        super();
        this.name = name;
        this.sex = sex;
    }

    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 String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
}

3. 映射文件  Teacher.hbm.xml ：

<hibernate-mapping package="cn.wh.vo">
    <class name="Teacher" table="t_teacher">
        <id name="id">
            <generator class="native"></generator>
        </id>
        <property name="name"/>
        <!-- 一对多的关联映射 -->
        <set name="students">
            <!-- key配置一的一端在多的一端的外键 -->
            <key column="tid"></key>
            <one-to-many class="Student"/>
        </set>
    </class>
</hibernate-mapping>

Student.hbm.xml:

<hibernate-mapping>
    <class name="cn.sxt.vo.Student" table="t_student">
        <id name="id">
            <generator class="native"></generator>
        </id>
        <property name="name"/>
        <property name="sex"/>
    </class>
</hibernate-mapping>

4. 测试：

public class HibernateTest {
    private Session session=null;
    @Before
    public void setUp(){
        session = HibernateUtil.getSession();
    }
    @After
    public void tearDown(){
        HibernateUtil.close();
    }
    @Test
    public void testCreateDB(){
        Configuration cfg = new Configuration().configure();
        SchemaExport export = new SchemaExport(cfg);
        //第一个参数  是否打印  数据库脚本
        //第二个参数 是否将脚本导入数据库执行
        export.create(true, true);
    }
    /**
     * 当关联映射是一对多时，保存数据时会多执行n条更新语句
     */
    @Test
    public void testInit(){
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            Teacher t1 = new Teacher("nico");
            Teacher t2 = new Teacher("michile");
            Student s1 = new Student("liming","男");
            Student s2 = new Student("hanmei","女");
            Student s3 = new Student("jim","男");
            t1.getStudents().add(s1);
            t1.getStudents().add(s2);
            t1.getStudents().add(s3);
            
            session.save(t1);
            session.save(t2);
            session.save(s1);
            session.save(s2);
            session.save(s3);
            tx.commit();
            
        } catch (Exception e) {
            if(tx!=null)
                tx.rollback();
        }
    }
    @Test
    public void testGet(){
        Teacher t = (Teacher) session.get(Teacher.class, 1);
        System.out.println("teacherName="+t.getName());
        System.out.println("=======================");
        for(Student s:t.getStudents()){
            System.out.println(s.getName()+"---"+s.getSex());
        }
    }
    
}