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

Course.hbm.xml


hibernate.cfg.xml