hibernate学习

hibernate多对多的解决
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。

/**
 * 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 teachers = new HashSet();

     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 getTeachers() {
         return teachers;
    }

     public void setTeachers(Set 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 teachers = new HashSet();

	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 getTeachers() {
		return teachers;
	}

	public void setTeachers(Set 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 courses = new HashSet();

     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 getCourses() {
         return courses;
    }

     public void setCourses(Set 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 courses = new HashSet();

	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 getCourses() {
		return courses;
	}

	public void setCourses(Set 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：
[list]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 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 cs = t1.getCourses();
		for (Course c : cs) {
			c.getTeachers().remove(t1);
		}

		session.delete(t1);
		session.getTransaction().commit();
		session.close();
	}

[/list]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。

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();
}

  /**
* 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();
} 

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)
    );