老師Teacher 與 課程Course 是一個多對多的關係，Pojo與XMl配置如下。
Pojo
Java代碼
/**
* Course Entity
* see table: tbl_course
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
public class Course {
private String id;
private String name;
private Set<Teacher> teachers = new HashSet<Teacher>();
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<Teacher> getTeachers() {
return teachers;
}
public void setTeachers(Set<Teacher> teachers) {
this.teachers = teachers;
}
}
/**
* Course Entity
* see table: tbl_course
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
public class Course {
private String id;
private String name;
private Set<Teacher> teachers = new HashSet<Teacher>();
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<Teacher> getTeachers() {
return teachers;
}
public void setTeachers(Set<Teacher> teachers) {
this.teachers = teachers;
}
}
Java代碼
/**
* Teacher Entity
* see table: tbl_teacher
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
public class Teacher {
private String id;
private String name;
private Set<Course> courses = new HashSet<Course>();
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<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
} }
/**
* Teacher Entity
* see table: tbl_teacher
*/
package com.leo.domain;
import java.util.HashSet;
import java.util.Set;
public class Teacher {
private String id;
private String name;
private Set<Course> courses = new HashSet<Course>();
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<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}}
配置文件也非常簡單：
Xml代碼
<?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.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代碼
<?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>
<?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>
先往數據庫裏插入一些記錄：
Java代碼
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);
/* 因爲主控方級聯設置爲save-update,如果設置爲none,則下面被註釋的代碼需要開啓，否則會報錯 */
//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);
/* 因爲主控方級聯設置爲save-update,如果設置爲none,則下面被註釋的代碼需要開啓，否則會報錯 */
//session.save(t1);
//session.save(t2);
session.save(c1);
session.getTransaction().commit();
session.close();
}
下面是測試的一些結果：
1. 如果cascade不管主控方設置還是被控方設置成 all, delete等與delete級聯刪除有關即可，兩端以及中間表的記錄都會被刪除，通常這樣的需要是很少的，因此，如果你要這樣的情況，只要簡單設置成all, delete就可以輕鬆的將關係以及兩端的記錄刪除的乾乾淨淨。
2. 只想刪除某一端的記錄以及中間的表的關聯信息。 這種需求通常是很常見的。這個時候cascade的設置是除與delete有關的任何級聯約束。以下是刪除心得：
如果刪除的是主控方，只需要簡單的刪除這條記錄，級聯關係以及主控方的記錄同時刪除，但被控方的記錄仍然存在。因此只對主控方的多對多刪除是最簡單，直接的。代碼如下：Java代碼
/**
* 多對多 主控方刪除(可以刪除中間表記錄)
*/
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();
}
/**
* 多對多 主控方刪除(可以刪除中間表記錄)
*/
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();
}
如果你這個時候想直接刪除被控方，那麼很遺憾的告訴你，你只做到了一半，你只是簡單的把被控方的記錄刪除了，關聯關係仍然存在中間表裏，系統隨時會因爲你的關聯訪問報錯，代碼如下：Java代碼
/**
* 多對多 被控方刪除(無法刪除中間表記錄)
*/
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();
}
/**
* 多對多 被控方刪除(無法刪除中間表記錄)
*/
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();
}
如果想既想刪除被控方，雙想刪除關聯，請看下面代碼：Java代碼
/**
* 多對多 被控方刪除(可以刪除中間表記錄)
*/
public void testDeleteByInverse2() {
String id = "402881ee175f04be01175f04c06c0002";
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();
}
/**
* 多對多 被控方刪除(可以刪除中間表記錄)
*/
public void testDeleteByInverse2() {
String id = "402881ee175f04be01175f04c06c0002";
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();
}
完成了。 但如果是Spring+Hiberante下多對多刪除，可能會報一個錯誤，目前的解決辦法是把兩端的cascade都設置成none. 初步斷定可能與事務有關，如果有人遇到了，並知道爲什麼，希望能留言，先謝謝大家了。
注：三個表的表結構
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)
);
===========================================================
只刪除中間表，可以通過以下代碼。
/**
* 多對多 通過主控方刪除中間表(其餘記錄都不變)
*/
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();
}
/**
* 多對多 通過被控方刪除中間表(其餘記錄都不變)
*/
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();
}
