Hibernate多对多的例子不少，但仔细一看，大多数都是保存的，删除谈的少，但问题还不少，因此有必须简单测试一下，以下我们来个简单的多对多关系建立
老师Teacher 与 课程Course 是一个多对多的关系，Pojo与XMl配置如下。
Pojo
Java代码
/**
* Course Entity
* see table: tbl_course
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
/**
* @author superleo
*
*/
public class Course {
private String id;
private String name;
private Set teachers = new HashSet();
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getTeachers() {
return teachers;
}
public void setTeachers(Set teachers) {
this.teachers = teachers;
}
}
/**
* Course Entity
* see table: tbl_course
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
/**
* @author superleo
*
*/
public class Course {
private String id;
private String name;
private Set teachers = new HashSet();
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getTeachers() {
return teachers;
}
public void setTeachers(Set teachers) {
this.teachers = teachers;
}
}
Java代码
/**
* Teacher Entity
* see table: tbl_teacher
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
/**
* @author superleo
*
*/
public class Teacher {
private String id;
private String name;
private Set courses = new HashSet();
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getCourses() {
return courses;
}
public void setCourses(Set courses) {
this.courses = courses;
}
}
/**
* Teacher Entity
* see table: tbl_teacher
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
/**
* @author superleo
*
*/
public class Teacher {
private String id;
private String name;
private Set courses = new HashSet();
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getCourses() {
return courses;
}
public void setCourses(Set courses) {
this.courses = courses;
}
}
配置文件也非常简单：
Xml代码
Xml代码
先往数据库里插入一些记录：
Java代码
public void testSave() {
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
// create course
Course c1 = new Course();
Course c2 = new Course();
c1.setName("C");
c2.setName("Java");
// create teacher
Teacher t1 = new Teacher();
Teacher t2 = new Teacher();
t1.setName("Leo");
t2.setName("Rose");
// create relationship
c1.getTeachers().add(t1);
c1.getTeachers().add(t2);
t1.getCourses().add(c1);
t2.getCourses().add(c1);
/* 因为主控方级联设置为save-update,如果设置为none,则下面被注释的代码需要开启，否则会报错 */
//session.save(t1);
//session.save(t2);
session.save(c1);
session.getTransaction().commit();
session.close();
}
public void testSave() {
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
// create course
Course c1 = new Course();
Course c2 = new Course();
c1.setName("C");
c2.setName("Java");
// create teacher
Teacher t1 = new Teacher();
Teacher t2 = new Teacher();
t1.setName("Leo");
t2.setName("Rose");
// create relationship
c1.getTeachers().add(t1);
c1.getTeachers().add(t2);
t1.getCourses().add(c1);
t2.getCourses().add(c1);
/* 因为主控方级联设置为save-update,如果设置为none,则下面被注释的代码需要开启，否则会报错 */
//session.save(t1);
//session.save(t2);
session.save(c1);
session.getTransaction().commit();
session.close();
}
下面是测试的一些结果：
1. 如果cascade不管主控方设置还是被控方设置成 all, delete等与delete级联删除有关即可，两端以及中间表的记录都会被删除，通常这样的需要是很少的，因此，如果你要这样的情况，只要简单设置成all, delete就可以轻松的将关系以及两端的记录删除的干干净净。
2. 只想删除某一端的记录以及中间的表的关联信息。 这种需求通常是很常见的。这个时候cascade的设置是除与delete有关的任何级联约束。以下是删除心得：
如果删除的是主控方，只需要简单的删除这条记录，级联关系以及主控方的记录同时删除，但被控方的记录仍然存在。因此只对主控方的多对多删除是最简单，直接的。代码如下：Java代码
/**
* 多对多 主控方删除(可以删除中间表记录)
*/
public void testDelete() {
String id = "402881ee175f04be01175f04c05d0001";
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Course c1 = (Course) session.get(Course.class, id);
session.delete(c1);
session.getTransaction().commit();
session.close();
}
/**
* 多对多 主控方删除(可以删除中间表记录)
*/
public void testDelete() {
String id = "402881ee175f04be01175f04c05d0001";
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Course c1 = (Course) session.get(Course.class, id);
session.delete(c1);
session.getTransaction().commit();
session.close();
}
如果你这个时候想直接删除被控方，那么很遗憾的告诉你，你只做到了一半，你只是简单的把被控方的记录删除了，关联关系仍然存在中间表里，系统随时会因为你的关联访问报错，代码如下：Java代码
/**
* 多对多 被控方删除(无法删除中间表记录)
*/
public void testDeleteByInverse() {
String id = "402881ee175a2e7c01175a2e7ead0003";
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Teacher t1 = (Teacher) session.get(Teacher.class, id);
session.delete(t1);
session.getTransaction().commit();
session.close();
}
/**
* 多对多 被控方删除(无法删除中间表记录)
*/
public void testDeleteByInverse() {
String id = "402881ee175a2e7c01175a2e7ead0003";
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Teacher t1 = (Teacher) session.get(Teacher.class, id);
session.delete(t1);
session.getTransaction().commit();
session.close();
}
如果想既想删除被控方，双想删除关联，请看下面代码：Java代码
/**
* 多对多 被控方删除(可以删除中间表记录)
*/
public void testDeleteByInverse2() {
String id = "402881ee175f04be01175f04c06c0002";
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Teacher t1 = (Teacher) session.get(Teacher.class, id);
Set cs = t1.getCourses();
for (Course c : cs) {
c.getTeachers().remove(t1);
}
session.delete(t1);
session.getTransaction().commit();
session.close();
}
/**
* 多对多 被控方删除(可以删除中间表记录)
*/
public void testDeleteByInverse2() {
String id = "402881ee175f04be01175f04c06c0002";
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Teacher t1 = (Teacher) session.get(Teacher.class, id);
Set cs = t1.getCourses();
for (Course c : cs) {
c.getTeachers().remove(t1);
}
session.delete(t1);
session.getTransaction().commit();
session.close();
}
完成了。 但如果是Spring+Hiberante下多对多删除，可能会报一个错误，目前的解决办法是把两端的cascade都设置成none. 初步断定可能与事务有关，如果有人遇到了，并知道为什么，希望能留言，先谢谢大家了。
注：三个表的表结构
1. tbl_course.sql
create table "SCOTT"."TBL_COURSE"(
"ID" VARCHAR2(80) not null,
"NAME" VARCHAR2(20) not null,
constraint "SYS_C005315" primary key ("ID")
);
create unique index "SCOTT"."SYS_C005315" on "SCOTT"."TBL_COURSE"("ID");
2. tbl_teacher.sql
create table "SCOTT"."TBL_TEACHER"(
"ID" VARCHAR2(80) not null,
"NAME" VARCHAR2(20) not null,
constraint "SYS_C005313" primary key ("ID")
);
create unique index "SCOTT"."SYS_C005313" on "SCOTT"."TBL_TEACHER"("ID");
3.tbl_teacher_course.sql
create table "SCOTT"."TBL_TEACHER_COURSE"(
"FK_TEACHER_ID" VARCHAR2(80),
"FK_COURSE_ID" VARCHAR2(90)
);
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