主题：Hibernate多对多删除有关问题的解决(一种方法)

主题：Hibernate多对多删除问题的解决(一种方法)

主题：Hibernate多对多删除问题的解决博客分类：?

HibernateHibernateXMLSQL.netSpringHibernate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<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;?

/**?
* @author superleo?
*?
*/?
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<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;?

/**?
* @author superleo?
*?
*/?
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;?
}?

}?


配置文件也非常简单：?

Xml代码?
<?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 />??
??????? </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 />??
??????? </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 />?
</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 />?
</set>?

</class>?
</hibernate-mapping>Xml代码?
<?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 />??
??????? </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 />??
??????? </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 />?
</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 />?
</set>?

</class>?
</hibernate-mapping>?

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();???
}??

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<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)?
??? );?