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hibernate多对多的解决(转)

xiaoxiao2021-11-25  15


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转[url]http://www.iteye.com/topic/154587[/url] 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 /** * 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; }} /** * 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 version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.leo.domain.Course" table="tbl_course" batch-size="100" dynamic-insert="true" dynamic-update="true"> <id name="id" column="id"> <generator class="uuid" /> </id> <property name="name" column="name" type="string" /> <set access="property" lazy="true" inverse="false" cascade="save-update" name="teachers" batch-size="10" fetch="select" table="tbl_teacher_course"> <key column="fk_course_id" /> <many-to-many class="com.leo.domain.Teacher" column="fk_teacher_id" /> </set> </class> </hibernate-mapping> <?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.leo.domain.Teacher" table="tbl_teacher" batch-size="100" dynamic-insert="true" dynamic-update="true"> <id name="id" column="id"> <generator class="uuid" /> </id> <property name="name" column="name" type="string" /> <set access="property" lazy="true" inverse="true" cascade="save-update" name="courses" batch-size="10" fetch="select" table="tbl_teacher_course"> <key column="fk_teacher_id" /> <many-to-many class="com.leo.domain.Course" column="fk_course_id" /> </set> </class> </hibernate-mapping> 先往数据库里插入一些记录: 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[color=#ff0000]cascade[/color]不管主控方设置还是被控方设置成 [color=#ff0000]all, delete[/color]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,[color=#ff0000]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。[/color] [color=#000000]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:[/color] [list]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: /** * 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: /** * 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: /** * 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(); } [/list]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。 只删除中间表,可以通过以下代码。 /*** 多对多 通过主控方删除中间表(其余记录都不变)*/public void testDeleteByInverse3() {String id = "402881ee1782dad9011782dadb310001";Session session = HibernateSessionFactory.getSession();session.beginTransaction();Course c1 = (Course) session.get(Course.class, id);c1.setTeachers(null);session.getTransaction().commit();session.close();}/*** 多对多 通过被控方删除中间表(其余记录都不变)*/public void testDeleteByInverse4() {String id = "402881ee1782dbd4011782dbd64a0002";Session session = HibernateSessionFactory.getSession();session.beginTransaction();Teacher t1 = (Teacher) session.get(Teacher.class, id);Set<Course> cs = t1.getCourses();for (Course c : cs) {c.getTeachers().remove(t1);}session.getTransaction().commit();session.close();} 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) ); 相关资源:hibernate的多对多案例