hibernate 多对多操作
关键字: hibernate 多对多操作
多对多的两种映射形式：
一。映射多对多关系
老师Teacher 与 课程Course 是一个多对多的关系，XMl配置如下。
三个表的表结构
1. tbl_course.sql
create table "SCOTT"."TBL_COURSE"(
"ID" CHAR(32) not null,
"NAME" VARCHAR2(20) not null,
constraint "SYS_C005315" primary key ("ID")
);
2. tbl_teacher.sql
create table "SCOTT"."TBL_TEACHER"(
"ID" CHAR(32) not null,
"NAME" VARCHAR2(20) not null,
constraint "SYS_C005313" primary key ("ID")
);
3.tbl_teacher_course.sql
create table "SCOTT"."TBL_TEACHER_COURSE"(
"TID" CHAR(32),
"CID" CHAR(32)
);
Teacher.hbm.xml
<hibernate-mapping>
<class name="mapping.Teacher" table="teacher" schema="dbo" catalog="Student">
<id name="id" type="string">
<column name="ID" length="32" />
<generator class="uuid" />
</id>
<property name="name" type="string">
<column name="Name" length="50" not-null="true" />
</property>
<set access="property" name="courses" lazy="true" inverse="true"
cascade="save-update" batch-size="10" fetch="select"
table="teacher_course">
<key column="TID" />
<many-to-many class="mapping.Course1" column="CID" />
</set>
</class>
</hibernate-mapping>
COURSE.hbm.xml
<hibernate-mapping>
<class name="mapping.Course" table="course" schema="dbo" catalog="Student">
<id name="id" type="string">
<column name="ID" length="32" />
<generator class="uuid" />
</id>
<property name="cname" type="string">
<column name="cname" length="50" />
</property>
<set access="property" name="teachers" lazy="true"
inverse="false"
cascade="save-update" batch-size="10" fetch="select" table="teacher_course">
<key column="CID" />
<many-to-many class="mapping.Teacher" column="TID" />
</set>
</class>
</hibernate-mapping>
1. 如果cascade 不管主控方设置还是被控方设置成all或delete，级联删除时，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。
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：
2.1 通过主控方来删除
/**
* 多对多 主控方删除(可以删除中间表记录)
*/
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
String cid = "2c2880d12041c65f012041c665180001";
Course course1 = (Course) session.get(Course.class , cid);
session.delete(course1);
session.getTransaction().commit();
session.close();
2.2 通过被控方来删除
/**
* 多对多 被控方删除(无法删除中间表记录)
*/
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(可以删除中间表记录)
*/
String id = "402881ee175a2e7c01175a2e7ead0003" ;
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.delete(t1);
session.getTransaction().commit();
session.close();
二。映射为两个一对多关系
三个表结构如下：
CREATE TABLE [dbo].[student] (
[id] [bigint] IDENTITY (1, 1) NOT NULL ,
[sno] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[sname] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[gender] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
CREATE TABLE [dbo].[score] (
[id] [bigint] IDENTITY (1, 1) NOT NULL ,
[cid] [bigint] NULL ,
[sid] [bigint] NULL ,
[scgrade] [float] NOT NULL
) ON [PRIMARY]
CREATE TABLE [dbo].[course] (
[id] [bigint] IDENTITY (1, 1) NOT NULL ,
[cno] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[cname] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL
) ON [PRIMARY]
Student.hbm.xml
<hibernate-mapping>
<class name="mapping.Student" table="student" schema="dbo" catalog="Student">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="identity" />
</id>
<set name="scores" cascade="all" inverse="true" table="score" >
<key>
<column name="sid" not-null="true" />
</key>
<one-to-many class="mapping.Score" />
</set>
</class>
</hibernate-mapping>
Score.hbm.xml
<hibernate-mapping>
<class name="mapping.Score" table="score" schema="dbo" catalog="Student">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="identity" />
</id>
<many-to-one name="course" class="mapping.Course" >
<column name="cid" />
</many-to-one>
<many-to-one name="student" class="mapping.Student" >
<column name="sid" />
</many-to-one>
</class>
</hibernate-mapping>
Course.hbm.xml
<hibernate-mapping>
<class name="mapping.Course" table="course" schema="dbo" catalog="Student">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="identity" />
</id>
<set name="scores" cascade="all" inverse="true" table="score">
<key>
<column name="cid" not-null="true" />
</key>
<one-to-many class="mapping.Score" />
</set>
</class>
</hibernate-mapping>
/**
* 一对多 被控方删除(可以删除中间表记录) 学生
*/
Long lid = Long.valueOf("19");
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Student student = (Student)session.get(Student.class, lid);
session.delete(student);
session.getTransaction().commit();
session.close();
/**
* 一对多 被控方删除(可以删除中间表记录) 课程
*/
Long lid = Long.valueOf("19");
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
Course course = (Course)session.get(Course.class, lid);
session.delete(course);
session.getTransaction().commit();
session.close();
另外从网上收集了一些资料，进行了整理，
附件内容包括一对一，一对多，多对多类型映射及详细说明。希望对学习hibernate的朋友有所帮助。
