Hibernate -- 映射多对多双向关联关系
1.
示例代码：
Student.java
package cn.itcast.many2many;
import java.util.HashSet;
import java.util.Set;
@SuppressWarnings("serial")
public class Student implements java.io.Serializable {
private Integer id;
private String name;
private Set<Course> courses=new HashSet(0);
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
}
Course.java
package cn.itcast.many2many;
import java.util.HashSet;
import java.util.Set;
@SuppressWarnings("serial")
public class Course implements java.io.Serializable{
private Integer id;
private String name;
private Set<Student> studentes=new HashSet(0);
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Student> getStudentes() {
return studentes;
}
public void setStudentes(Set<Student> studentes) {
this.studentes = studentes;
}
}
App.java
package cn.itcast.many2many;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App {
private static SessionFactory sf=null;
static{
Configuration config=new Configuration();
config.configure("cn/itcast/many2many/hibernate.cfg.xml");
config.addClass(Student.class);
config.addClass(Course.class);
sf=config.buildSessionFactory();
}
/*
* 知识点4:测试保存
*/
@Test
public void saveStudentAndCoure(){
Session session=sf.openSession();
Transaction tx=session.beginTransaction();
Student s1=new Student();
s1.setName("风侠");
Student s2=new Student();
s2.setName("雨侠");
Course c1=new Course();
c1.setName("语文");
Course c2=new Course();
c2.setName("数学");
//建立关联关系
s1.getCourses().add(c1);
s1.getCourses().add(c2);
s2.getCourses().add(c1);
s2.getCourses().add(c2);
c1.getStudentes().add(s1);
c1.getStudentes().add(s2);
c2.getStudentes().add(s1);
c2.getStudentes().add(s2);
session.save(s1);
session.save(s2);
session.save(c1);
session.save(c2);
tx.commit();
session.close();
}
//知识点5:解除1号学生和1号课程的关联关系
@Test
public void removeMany2Many(){
Session session=sf.openSession();
Transaction tx=session.beginTransaction();
//查询1号学生
Student s1=(Student)session.get(Student.class, 1);
//查询1号课程
Course c1=(Course)session.get(Course.class, 1);
//解除关联关系
s1.getCourses().remove(c1);
c1.getStudentes().remove(s1);
tx.commit();
session.close();
}
//知识点6:改变1号学生和2号课程的关联关系,改为1号学生和1号课程
@Test
public void changeMany2Many(){
Session session=sf.openSession();
Transaction tx=session.beginTransaction();
//查询1号学生
Student s1=(Student)session.get(Student.class, 1);
//查询1号课程
Course c1=(Course)session.get(Course.class, 1);
//查询2号课程
Course c2=(Course)session.get(Course.class, 2);
//解除1号学生和2号课程关联关系
s1.getCourses().remove(c2);
c2.getStudentes().remove(s1);
//建立1号学生和1号课程的关联关系
s1.getCourses().add(c1);
c1.getStudentes().add(s1);
tx.commit();
session.close();
}
//知识点7:删除2号学生,产生异常
@Test
public void removeStudent(){
Session session=sf.openSession();
Transaction tx=session.beginTransaction();
//查询2号学生
Student s2=(Student)session.get(Student.class, 2);
session.delete(s2);
tx.commit();
session.close();
}
/*
* 知识点8:删除1号课程.这里能删除,因为课程是主控方法 student.hbm.xml配置inverse="true"
* * 能删除1号课程
* * 能删除1号课程对应的中间表信息,但不能是删除学生表的信息
*/
@Test
public void removeCourse(){
Session session=sf.openSession();
Transaction tx=session.beginTransaction();
//查询1号课程
Course c1=(Course)session.get(Course.class, 1);
session.delete(c1);
tx.commit();
session.close();
}
//知识点9:删除1号课程的同时,要把1号和2号学生删掉？ cascade="delete", 中间表用到的学生应先删除
@Test
public void removeCourseCase(){
Session session=sf.openSession();
Transaction tx=session.beginTransaction();
//查询1号课程
Course c1=(Course)session.get(Course.class, 1);
session.delete(c1);
tx.commit();
session.close();
}
}
Student.hbm.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="cn.itcast.many2many.Student" table="student">
<id name="id" type="integer">
<column name="id"/>
<generator class="increment"/>
</id>
<property name="name" type="string">
<column name="name"/>
</property>
<!--table为中间表-->
<set name="courses" table="student_course" inverse="true">
<!--coursees这个集合中放置的是课程对象
通过中间表的学生id,查询该学生要学习的课程
select cid from student_course where sid=1
-->
<key column="sid"/>
<!-- class表示coursees集合存放的是什么类型的对象
column="cid":通过课程id获取课程对象
select id,name from course where id=cid;
-->
<many-to-many class="cn.itcast.many2many.Course" column="cid"/>
</set>
</class>
</hibernate-mapping>
Course.hbm.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="cn.itcast.many2many.Course" table="course">
<id name="id" type="integer">
<column name="id"/>
<generator class="increment"/>
</id>
<property name="name" type="string">
<column name="name"/>
</property>
<!--table为中间表-->
<set name="studentes" table="student_course" cascade="delete">
<!--coursees这个集合中放置的是课程对象
通过中间表的学生id,查询该学生要学习的课程
select cid from student_course where sid=1
-->
<key column="cid"/>
<!-- class表示coursees集合存放的是什么类型的对象
column="cid":通过课程id获取课程对象
select id,name from course where id=cid;
-->
<many-to-many class="cn.itcast.many2many.Student" column="sid"/>
</set>
</class>
</hibernate-mapping>
hibernate.cfg.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>
<!-- 配置数据库的方言,让hibernate知道连接的是哪个数据库-->
<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
<!-- 配置利用javaBean和映射文件生成数据库中的表
hibernate.hbm2ddl.auto值
* create:执行时，先查找该表是否存在,如存在先删除表，在创建表
* none:不能创建表,只能往表中插入数据,如表不存在抛出异常,默认值
* update:执行时，
情况一:
先查找该表是否存在,如果表存在,直接插入,如果表不存在,先创建表，再插入数据.
情况二:
先查找该表是否存在,如果表存在,但表的结构不一样,要修改表的结构
-->
<property name="hibernate.hbm2ddl.auto">update</property>
<!-- 显示hibernate生成的sql语句 -->
<property name="hibernate.show_sql">true</property>
<!-- 显示格式化得sql语句 -->
<property name="hibernate.format_sql">false</property>
</session-factory>
</hibernate-configuration>
