这里讲继承类的映射,上一篇博客中的例子里面学生有照片,但是照片又可以分为生活照和工作照,在这里照片类就是父类,工作照和生活照就是两个子类。这里具有继承关系的类怎么通过hibernate映射保存到数据库中呢?
主要有三种方式:每个具体类对应一个表、根类对应一个表、每个类对应一个表。
先看第一种:每个具体类对应一个表:这种方式是抽象的父类不保存在数据库中,而是把子类保存到数据库中
1.新建工程Hibernate07;
2.新建相片类Image:
package com.test.model;
public abstract class Image {
private int id;
private String imageName;
private Student student;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getImageName() {
return imageName;
}
public void setImageName(String imageName) {
this.imageName = imageName;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
}
这里的相片类是一个抽血类,不能实例化。
3.新建生活照类:
package com.test.model;
public class LifeImage extends Image{
}
这里就是一个空的类继承自照片类Image,这样的话这个类也就有了Image的属性和方法。
4.新建工作照类:
package com.test.model;
public class WorkImage extends Image{
}
5.新建学生类Student:
package com.test.model;
import java.util.Set;
public class Student {
private int id;
private String name;
private Set<Image> images;
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<Image> getImages() {
return images;
}
public void setImages(Set<Image> images) {
this.images = images;
}
}
学生与照片是一对多关系,这里使用集合Set表示学生的照片属性。
6.写学生类映射函数:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.test.model">
<class name="Student" table="t_student">
<id name="id" column="stuId">
<generator class="native"></generator>
</id>
<property name="name" column="stuName"></property>
</class>
</hibernate-mapping>
这里并没有写属性images的映射配置,这是因为Image类是抽象类,不能添加到数据库表中。
7.生活照类映射文件:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.test.model">
<class name="LifeImage" table="t_lifeImage">
<id name="id" column="lifeImageId">
<generator class="native"></generator>
</id>
<property name="imageName" column="imageName"></property>
<many-to-one name="student" column="stuId" class="com.test.model.Student"></many-to-one>
</class>
</hibernate-mapping>
这里配置了数据库表t_lifeImage具有外键stuId,外键对应的是表t_student的主键。
8.写工作照类的映射文件:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.test.model">
<class name="WorkImage" table="t_workImage">
<id name="id" column="workImageId">
<generator class="native"></generator>
</id>
<property name="imageName" column="imageName"></property>
<many-to-one name="student" column="stuId" class="com.test.model.Student"></many-to-one>
</class>
</hibernate-mapping>
9.写配置文件:
<?xml version='1.0' encoding='utf-8'?>
<!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>
<!--数据库连接设置 -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<!-- 方言 -->
<property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
<!-- 控制台显示SQL -->
<property name="show_sql">true</property>
<!-- 自动更新表结构 -->
<property name="hbm2ddl.auto">update</property>
<mapping resource="com/test/model/Student.hbm.xml"/>
<mapping resource="com/test/model/LifeImage.hbm.xml"/>
<mapping resource="com/test/model/WorkImage.hbm.xml"/>
</session-factory>
</hibernate-configuration>
10.写测试函数StudentTest:
package com.test.service;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.test.model.Image;
import com.test.model.Image2;
import com.test.model.Image3;
import com.test.model.Student2;
import com.test.model.Student3;
import com.test.util.HibernateUtil;
public class StudentTest {
private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
private Session session;
@Before
public void setUp() throws Exception {
session=sessionFactory.openSession(); // 生成一个session
session.beginTransaction(); // 开启事务
}
@After
public void tearDown() throws Exception {
session.getTransaction().commit(); // 提交事务
session.close(); // 关闭session
}
@Test
public void testGetAllImages(){
}
}
运行一下函数testGetAllimages,看一下生成的数据表:
这里给这三个表添加一部分数据:
10.修改一下测试函数:
@Test
public void testGetAllImages(){
List<Image> imageList = new ArrayList<Image>();
int stuId = 1;
List<Image> lifeImageList = (List<Image>)session.createQuery("from LifeImage l where l.student.id="+stuId).list();
imageList.addAll(lifeImageList);
List<Image> workImageList = (List<Image>)session.createQuery("from WorkImage w where w.student.id="+stuId).list();
imageList.addAll(workImageList);
Iterator it = imageList.iterator();
while(it.hasNext()){
Image image =(Image)it.next();
System.out.println(image.getImageName());
}
}
由于t_student表中没有Image的信息,这里只能通过从生活照表和工作照表中取出存入的数据信息。运行方法:
这里取出了照片的信息。