Hibernate中，One2Many的基于注解Annotation的实现

柔光的暖阳◎ 2022-09-24 01:21 92阅读 0赞

1、在Hibernate中，One2Many的基于注解Annotation的实现

2、Student.java的代码（带注解，**注意注解是在哪个包下的**）

import javax.persistence.Table;
    
    @Entity
    @Table(name = "student")
    public class Student {
    	@Id
    	@GeneratedValue
    	private int id;
    	@Column(name = "age")
    	private int age;
    	private String name;
    
    	// get set
    }

3、ClassRoom.java的代码（带注解，**注意注解是在哪个包下的**）

import javax.persistence.Table;
    
    @Entity
    @Table(name = "classroom")
    public class ClassRoom {
    	@Id
    	@GeneratedValue
    	private int id;
    	@Column(name = "classRoomName")
    	private String classRoomName;
    
    	/**
    	 * 无论是一对多，还是多对一 。都需要，并且可以，在多的一方建立外键
    	 */
    	// 持有一方的set集合
    	// 使用注解的时候，默认不使用懒加载
    	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    	@JoinColumn(name = "classid")
    	// 对应儿子类的哪个字段
    	private Set<Student> stus = new HashSet<Student>();
    
    	// get set
    }

4、hibernate.cfg.xml的配置

4.1 将Student.java和ClassRoom.java，加入到hibernate.cfg.xml的配置文件里面

<mapping class="com.hibernate.entity.ClassRoom" />
    		<mapping class="com.hibernate.entity.Student" />

4.2  hibernate.cfg.xml的配置的完整内容

<!DOCTYPE hibernate-configuration PUBLIC
    	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    
    <hibernate-configuration>
    	
    	<session-factory>
    
    		
    		<property name="hibernate.connection.driver_class">
    			com.mysql.jdbc.Driver
    		</property>
    		<property name="hibernate.connection.url">
    			jdbc:mysql:///hibernate
    		</property>
    		<property name="hibernate.connection.username">root</property>
    		<property name="hibernate.connection.password">1234</property>
    		
    		<property name="hibernate.dialect">
    			org.hibernate.dialect.MySQL5Dialect
    		</property>
    
    
    		
    		
    		<property name="hibernate.show_sql">true</property>
    		
    		<property name="hibernate.format_sql">true</property>
    		
    		<property name="hibernate.hbm2ddl.auto">update</property>
    
    		
    		<mapping class="com.hibernate.entity.ClassRoom" />
    		<mapping class="com.hibernate.entity.Student" />
    	</session-factory>
    </hibernate-configuration>

5、测试代码

public class HibernateTest {
    
    	@Test
    	public void testone2many() {
    
    		Student stu1 = new Student();
    		stu1.setAge(18);
    		stu1.setName("18");
    
    		Student stu2 = new Student();
    		stu2.setAge(19);
    		stu2.setName("19");
    
    		ClassRoom classRoom = new ClassRoom();
    		classRoom.setClassRoomName("计算机技术");
    		// 增加ClassRoom和Student的注册关系
    		classRoom.getStus().add(stu1);
    		classRoom.getStus().add(stu2);
    
    		// 保存到数据库
    		IClassRoomDao roomDao = new ClassRoomDaoImpl();
    		IStudentDao studentDao = new StudentDaoImpl();
    
    		// 先保存多的一方
    
    		studentDao.add(stu1);
    		studentDao.add(stu2);
    
    		// 在保存一的一方
    		roomDao.add(classRoom);
    
    	}
    
    	@Test
    	public void test2() {
    		// Session
    		Session session = null;
    		try {
    			session = HibernateUtils.openSession();
    			ClassRoom classRoom = (ClassRoom) session.get(ClassRoom.class, 1);
    			System.out.println(classRoom.getStus().size());
    		} catch (Exception e) {
    		}
    
    	}
    }

6、程序的运行结果

![20160722123025166][]

7、代码下载

[代码下载][Link 1]

[20160722123025166]: /images/20220720/e67587199c1c45c1812981f4208294a1.png
[Link 1]: http://pan.baidu.com/s/1o8J9WXs