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：  Hibernate

Hibernate XML SQL .net Spring

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) 
    );