Hibernate多对多删除

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

/**
 * 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;
	}

}

/**
 * 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
 
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
 
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：

 

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：

  /**
       * 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：

  /**
   * 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();
  }

  	/**
  	 * 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：

  /**
   * 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();
  }

  	/**
  	 * 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)
    );

 

 

如果只想删除中间表记录呢？

 

只删除中间表，可以通过以下代码。

/**
* 多对多 通过主控方删除中间表(其余记录都不变)
*/
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();
}


/**
* 多对多 通过被控方删除中间表(其余记录都不变)
*/
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();
}