Hibernate -- 映射多对多双向关联关系

1.

示例代码：

Student.java

package cn.itcast.many2many;

import java.util.HashSet;
import java.util.Set;

@SuppressWarnings("serial")
public class Student implements java.io.Serializable {

	private Integer id;
	private String name;
	private Set<Course> courses=new HashSet(0);

	public Integer getId() {
		return id;
	}
	public void setId(Integer 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;
	}
}

Course.java

package cn.itcast.many2many;

import java.util.HashSet;
import java.util.Set;

@SuppressWarnings("serial")
public class Course  implements java.io.Serializable{
	private Integer id;
	private String name;
	private Set<Student> studentes=new HashSet(0);

	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Set<Student> getStudentes() {
		return studentes;
	}
	public void setStudentes(Set<Student> studentes) {
		this.studentes = studentes;
	}
}

App.java

package cn.itcast.many2many;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

public class App {
	private static  SessionFactory sf=null;

	static{
		   Configuration config=new Configuration();
	       config.configure("cn/itcast/many2many/hibernate.cfg.xml");
	       config.addClass(Student.class);
	       config.addClass(Course.class);
	       sf=config.buildSessionFactory();
	}

    /*
     * 知识点4:测试保存
     */
	@Test
	public  void saveStudentAndCoure(){
		   Session session=sf.openSession();
		   Transaction tx=session.beginTransaction();

		   Student s1=new Student();
		   s1.setName("风侠");

		   Student s2=new Student();
		   s2.setName("雨侠");

		   Course c1=new Course();
		   c1.setName("语文");

		   Course c2=new Course();
		   c2.setName("数学");

		   //建立关联关系
		   s1.getCourses().add(c1);
		   s1.getCourses().add(c2);

		   s2.getCourses().add(c1);
		   s2.getCourses().add(c2);

		   c1.getStudentes().add(s1);
		   c1.getStudentes().add(s2);

		   c2.getStudentes().add(s1);
		   c2.getStudentes().add(s2);

		   session.save(s1);
		   session.save(s2);
		   session.save(c1);
		   session.save(c2);

		   tx.commit();
		   session.close();
	}

	//知识点5:解除1号学生和1号课程的关联关系
	@Test
	public  void removeMany2Many(){
		   Session session=sf.openSession();
		   Transaction tx=session.beginTransaction();

		   //查询1号学生
		   Student s1=(Student)session.get(Student.class, 1);

		   //查询1号课程
		   Course c1=(Course)session.get(Course.class, 1);

		   //解除关联关系
		   s1.getCourses().remove(c1);
		   c1.getStudentes().remove(s1);

		   tx.commit();
		   session.close();
	}

	//知识点6:改变1号学生和2号课程的关联关系,改为1号学生和1号课程
	@Test
	public  void changeMany2Many(){
		   Session session=sf.openSession();
		   Transaction tx=session.beginTransaction();

		   //查询1号学生
		   Student s1=(Student)session.get(Student.class, 1);

		   //查询1号课程
		   Course c1=(Course)session.get(Course.class, 1);

		   //查询2号课程
		   Course c2=(Course)session.get(Course.class, 2);

		   //解除1号学生和2号课程关联关系
		   s1.getCourses().remove(c2);
		   c2.getStudentes().remove(s1);

		   //建立1号学生和1号课程的关联关系
		   s1.getCourses().add(c1);
		   c1.getStudentes().add(s1);

		   tx.commit();
		   session.close();
	}

	//知识点7:删除2号学生,产生异常
	@Test
	public  void removeStudent(){
		   Session session=sf.openSession();
		   Transaction tx=session.beginTransaction();

		   //查询2号学生
		   Student s2=(Student)session.get(Student.class, 2);
		   session.delete(s2);

		   tx.commit();
		   session.close();
	}

	/*
	 * 知识点8:删除1号课程.这里能删除,因为课程是主控方法 student.hbm.xml配置inverse="true"
	 *   * 能删除1号课程
	 *   * 能删除1号课程对应的中间表信息,但不能是删除学生表的信息
	 */
	@Test
	public  void removeCourse(){
		   Session session=sf.openSession();
		   Transaction tx=session.beginTransaction();

		   //查询1号课程
		   Course c1=(Course)session.get(Course.class, 1);
		   session.delete(c1);

		   tx.commit();
		   session.close();
	}

	//知识点9:删除1号课程的同时,要把1号和2号学生删掉？  cascade="delete", 中间表用到的学生应先删除
	@Test
	public  void removeCourseCase(){
		   Session session=sf.openSession();
		   Transaction tx=session.beginTransaction();

		   //查询1号课程
		   Course c1=(Course)session.get(Course.class, 1);
		   session.delete(c1);

		   tx.commit();
		   session.close();
	}

}

Student.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <hibernate-mapping>
   <class name="cn.itcast.many2many.Student" table="student">

      <id name="id" type="integer">
        <column name="id"/>
        <generator class="increment"/>
      </id>
      <property name="name" type="string">
          <column name="name"/>
      </property>

      <!--table为中间表-->
      <set name="courses" table="student_course" inverse="true">
          <!--coursees这个集合中放置的是课程对象
              通过中间表的学生id,查询该学生要学习的课程
              select cid from student_course where sid=1
           -->
          <key  column="sid"/>
          <!-- class表示coursees集合存放的是什么类型的对象
              column="cid":通过课程id获取课程对象
              select id,name from course where id=cid;
          -->
          <many-to-many class="cn.itcast.many2many.Course" column="cid"/>
      </set>
  </class>

  </hibernate-mapping>

Course.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <hibernate-mapping>
   <class name="cn.itcast.many2many.Course" table="course">
      <id name="id" type="integer">
        <column name="id"/>
        <generator class="increment"/>
      </id>

      <property name="name" type="string">
          <column name="name"/>
      </property>

      <!--table为中间表-->
      <set name="studentes" table="student_course" cascade="delete">
          <!--coursees这个集合中放置的是课程对象
              通过中间表的学生id,查询该学生要学习的课程
              select cid from student_course where sid=1
           -->
          <key  column="cid"/>
          <!-- class表示coursees集合存放的是什么类型的对象
              column="cid":通过课程id获取课程对象
              select id,name from course where id=cid;
          -->
          <many-to-many class="cn.itcast.many2many.Student" column="sid"/>
      </set>
  </class>

  </hibernate-mapping>

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
   <session-factory>
      <property name="hibernate.connection.username">root</property>
      <property name="hibernate.connection.password">root</property>
      <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
      <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>

      <!-- 配置数据库的方言,让hibernate知道连接的是哪个数据库-->
      <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>

      <!-- 配置利用javaBean和映射文件生成数据库中的表
           hibernate.hbm2ddl.auto值
              * create:执行时，先查找该表是否存在,如存在先删除表，在创建表
              * none:不能创建表,只能往表中插入数据,如表不存在抛出异常,默认值
              * update:执行时，
                          情况一:
                                先查找该表是否存在,如果表存在,直接插入,如果表不存在,先创建表，再插入数据.
                          情况二:
                                先查找该表是否存在,如果表存在,但表的结构不一样,要修改表的结构
       -->
      <property name="hibernate.hbm2ddl.auto">update</property>

      <!-- 显示hibernate生成的sql语句 -->
      <property name="hibernate.show_sql">true</property>

      <!-- 显示格式化得sql语句 -->
      <property name="hibernate.format_sql">false</property>

   </session-factory>
</hibernate-configuration>