【7.2】双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

public class Student {
	private int id;
	private String name;
	private int age;
	private Grade grade;
//get…set
}

---

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

　　

3.映射文件

Grade.hbm.xml

<hibernate-mapping package="cn.siggy.pojo">
	<class name="Grade">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="name"/>
		<!-- set是 Grade中的集合属性  name属性名称 -->
		<set name="students">
			<!-- key表示外键  column外键列名-->
			<key column="grade_id"></key>
			<!-- one-to-many 一对多  类Grade 中  students 所表示类型 -->
			<one-to-many class="Student"/>
		</set>
	</class>
</hibernate-mapping>

　

Student.hbm.xml

<hibernate-mapping package="cn.siggy.pojo">
	<class name="Student">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="name"/>
		<property name="age"/>
		<many-to-one name="grade" class="Grade" column="grade_id" not-null="true"></many-to-one>
	</class>
</hibernate-mapping>

　　

4.测试代码

public class HibernateTest {
	@Test
	public void testCreateDB(){
		Configuration cfg = new Configuration().configure();
		SchemaExport se = new SchemaExport(cfg);
		//第一个参数 是否生成ddl脚本  第二个参数  是否执行到数据库中
		se.create(true, true);
	}
	@Test
	public void testSave() throws HibernateException, SerialException, SQLException{
		Session session = null;
		Transaction tx = null;
		try{
			session = HibernateUtil.getSession();
			tx = session.beginTransaction();
			Grade grade = new Grade();
			grade.setName("基础");
			
			Student stu = new Student();
			stu.setName("张三疯");
			stu.setAge(22);
			stu.setGrade(grade);
			Student stu1 = new Student();
			stu1.setName("老王");
			stu1.setAge(23);
			stu1.setGrade(grade);
			//关联
			//保存数据的顺序 是根据外键的配置来决定的
			//如果外键不能为null,那么先保存一的一端
			//如果外键可以为null,则可以随意保存
			session.save(grade);
			session.save(stu);
			session.save(stu1);
			
			tx.commit();
			
		}catch (HibernateException e) {
			if(tx!=null)
				tx.rollback();
			e.printStackTrace();
			throw e;
		}finally{
			HibernateUtil.closeSession();
		}
	}
	@Test
	public void testGet(){
		Session session = null;
		Transaction tx = null;
		try{
			session = HibernateUtil.getSession();
			tx = session.beginTransaction();
			//取数据
			Grade grade = (Grade)session.get(Grade.class, 1);
			System.out.println("gradeName="+grade.getName());
			System.out.println("grade所对应的多的一端的数据");
			Iterator<Student> iter = grade.getStudents().iterator();
			for(;iter.hasNext();){
				Student temp = iter.next();
				System.out.println("name="+temp.getName()+"\tage="+temp.getAge());
			}
			System.out.println("========================");
			Student stu = (Student)session.get(Student.class, 1);
			System.out.println("studentname="+stu.getName()+"   gradeName="+stu.getGrade().getName());
			tx.commit();
		}catch (HibernateException e) {
			if(tx!=null)
				tx.rollback();
			e.printStackTrace();
			throw e;
		}finally{
			HibernateUtil.closeSession();
		}
	}
}

　　

5.测试结果