主题：Hibernate多对多删除问题的解决

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<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 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 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)
    );