hibernate多对多映射关系

以下通过一个案例来讲解hirbernate多对多的应用

通过一个持久化类Student,和一个持久化类Course类

以下是二者的Student.hbm.xml和Course.hbm.xml

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">
<!--
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="hibernatetest2.Student" table="student" catalog="wuliu">
        <id name="sid" type="java.lang.Integer">
            <column name="sid" />
            <generator class="native" />
        </id>
        <property name="sname" type="java.lang.String">
            <column name="sname" length="20" not-null="true" />
        </property>
        <property name="sinfo" type="java.lang.String">
            <column name="sinfo" length="20" not-null="true" />
        </property>
        <property name="cid" type="java.lang.Integer">
            <column name="cid" not-null="true" />
        </property>
        <!-- 写多对一的外键以及类属性 -->
<!--         <many-to-one name="classes" column="cid" class="hibernatetest2.Classes">  -->
<!--         </many-to-one> -->
        <set name="course" table="stu_cur" inverse="false" cascade="all"><!-- 此处需要加入一个中间连接表的表名 -->
           <key column="sid"></key><!-- student表与中间表相关联的字段 -->
           <many-to-many class="hibernatetest3.Course" column="csid"></many-to-many><!-- 对方表(Course表)与中间表相关联的字段 -->
        </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">
<!--
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="hibernatetest3.Course" table="course" catalog="wuliu">
        <id name="csid" type="java.lang.Integer">
            <column name="csid" />
            <generator class="native" />
        </id>
        <property name="cname" type="java.lang.String">
            <column name="cname" length="20" not-null="true" />
        </property>
        <property name="cinfo" type="java.lang.String">
            <column name="cinfo" length="20" not-null="true" />
        </property>
        <property name="cscore" type="java.lang.Integer">
            <column name="cscore" not-null="true" />
        </property>
        <set name="student" table="stu_cur" inverse="true" cascade="none">
          <key column="csid"></key>
          <many-to-many class="hibernatetest2.Student" column="sid"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

持久化类Student

package hibernatetest2;

import hibernatetest3.Course;

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

/**
 * Student entity. @author MyEclipse Persistence Tools
 */

public class Student implements java.io.Serializable {
    // Fields
    private Integer sid;
    private String sname;
    private String sinfo;
    private Integer cid;
    private Classes classes;
    //设置一方的Set
    private Set<Course> course=new HashSet<Course>();
 
    // Constructors
    public Set<Course> getCourse() {
        return course;
    }
    public void setCourse(Set<Course> course) {
        this.course = course;
    }
    /** default constructor */
    public Student() {
    }
    /** full constructor */
    public Student(String sname, String sinfo, Integer cid) {
        this.sname = sname;
        this.sinfo = sinfo;
        this.cid = cid;
    }
    // Property accessors
    public Integer getSid() {
        return this.sid;
    }
    public void setSid(Integer sid) {
        this.sid = sid;
    }
    public String getSname() {
        return this.sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public String getSinfo() {
        return this.sinfo;
    }
    public void setSinfo(String sinfo) {
        this.sinfo = sinfo;
    }
    public Integer getCid() {
        return this.cid;
    }
    public void setCid(Integer cid) {
        this.cid = cid;
    }
    public Classes getClasses() {
        return classes;
    }
    public void setClasses(Classes classes) {
        this.classes = classes;
    }
    @Override
    public String toString() {
        return "Student [sid=" + sid + ", sname=" + sname + ", sinfo=" + sinfo
                + ", cid=" + cid +  "]";
    }   
}

Course持久化类

package hibernatetest3;

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



/**
 * Course entity. @author MyEclipse Persistence Tools
 */

public class Course  implements java.io.Serializable {
    // Fields    
     private Integer csid;
     private String cname;
     private String cinfo;
     private Integer cscore;
     //设置多方的Set
     private Set<Course> student=new HashSet<Course>();
    // Constructors
    public Set<Course> getStudent() {
        return student;
    }
    public void setStudent(Set<Course> student) {
        this.student = student;
    }
    /** default constructor */
    public Course() {
    }
    /** full constructor */
    public Course(String cname, String cinfo, Integer cscore) {
        this.cname = cname;
        this.cinfo = cinfo;
        this.cscore = cscore;
    }
    // Property accessors
    public Integer getCsid() {
        return this.csid;
    }
    public void setCsid(Integer csid) {
        this.csid = csid;
    }
    public String getCname() {
        return this.cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public String getCinfo() {
        return this.cinfo;
    }
    public void setCinfo(String cinfo) {
        this.cinfo = cinfo;
    }
    public Integer getCscore() {
        return this.cscore;
    }
    public void setCscore(Integer cscore) {
        this.cscore = cscore;
    }
    @Override
    public String toString() {
        return "Course [csid=" + csid + ", cname=" + cname + ", cinfo=" + cinfo
                + ", cscore=" + cscore + ", student=" + student + "]";
    }
}

测试类TestCourse

package hibernatetest3;

import hibernatetest2.Student;

import java.util.Iterator;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class TestCourse {
    private Configuration config;
    private SessionFactory sessionFactory;
    private Session session;
    private Transaction tx;
    @Before
    public void init(){
        config=new Configuration().configure();
        sessionFactory=config.buildSessionFactory();
        session=sessionFactory.openSession();
        tx=session.beginTransaction();
    }
    @After
    public void destory(){
        tx.commit();
        session.close();
    }
    //查询指定学生选择的课程
    @Test
    public void  searchTest(){
        //查找出学生id为2选择的所有的课程
//        Student stu=(Student)session.get(Student.class,2);
//        Set set=stu.getCourse();
//        Iterator<Course> it=set.iterator();
//        while(it.hasNext()){
//            System.out.println(it.next());
//        }
        //指定课程id 根据课程查找出有哪些学生选择该课程
        Course cur=(Course)session.get(Course.class,2);
        Set set=cur.getStudent();
        Iterator<Student> it=set.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }   
    }
    @Test
    public void addTest(){
//        //构造学生，进行选课
//        Student stu=new Student("张超","信管一班",2);
//        //选择出两个课程，然后进行选择
//        Course course2=(Course)session.get(Course.class,2);
//        Course course3=(Course)session.get(Course.class,3);
//        stu.getCourse().add(course3);
//        stu.getCourse().add(course2);
//        session.save(stu);
        //新增课程，由学生进行选课
        Course cur=new Course("Struts2","很难",6);
        //查找两个学生，然后将课程放入学生
        Student stu1=(Student)session.get(Student.class,1);
        Student stu2=(Student)session.get(Student.class,2);
        stu1.getCourse().add(cur);
        stu2.getCourse().add(cur);
        session.save(cur);
    }
    @Test//学生编号为2的学生选课选错了，需要修改
    public void updateTest(){
        //先找到学生ID为2的学生
        Student stu2=(Student)session.get(Student.class,2);
        //再找到已经选择错了的课，和即将要选择的课程
        Course cur5=(Course)session.get(Course.class,6);
        Course cur6=(Course)session.get(Course.class,5);
        stu2.getCourse().remove(cur5);
        stu2.getCourse().add(cur6);
        session.update(stu2);//需要在学生所对应的类里面将inverse改写成false，即表示Student类自身进行更改
        
    }
    @Test
    public void deleteTest(){
        //删除编号为2的学生所选的课,先找到编号为2的学生
        Student stu2=(Student)session.get(Student.class,4);
        session.delete(stu2);//如果选择delete,则会级联删除与之关联的所有对象
    }
}
注意在打印输出Student类的对象时，不能再Student类里面的toString()方法和Course类的toString()方法里同时写入Course对象属性和Student对象属性，否则会进入一个死循环。