Hibernate的多对多实例

在完成了一对多的实例的基础上，继续做多对多实例。例子是老师和学生，一个老师教多个学生，一个学生也有多个老师。

文档结构如图：

Student.java和Teacher.java的代码为：

package cn.hibernate.manytomany;

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

public class Student {
    private int stuId;
    private String stuName;
    private Set<Teacher> teachers = new HashSet<Teacher>();

    public Student(){
        
    }
    
    public Student(int stuId, String stuName, Set<Teacher> teachers) {
        this.stuId = stuId;
        this.stuName = stuName;
        this.teachers = teachers;
    }
    public int getStuId() {
        return stuId;
    }
    public void setStuId(int stuId) {
        this.stuId = stuId;
    }
    public String getStuName() {
        return stuName;
    }
    public void setStuName(String stuName) {
        this.stuName = stuName;
    }
    public Set<Teacher> getTeachers() {
        return teachers;
    }
    public void setTeachers(Set<Teacher> teachers) {
        this.teachers = teachers;
    }
}

package cn.hibernate.manytomany;

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

public class Teacher {
    private int teaId;
    private String teaName;
    private Set<Student> stus = new HashSet<Student>();
    public int getTeaId() {
        return teaId;
    }
    public void setTeaId(int teaId) {
        this.teaId = teaId;
    }
    public String getTeaName() {
        return teaName;
    }
    public void setTeaName(String teaName) {
        this.teaName = teaName;
    }
    public Set<Student> getStus() {
        return stus;
    }
    public void setStus(Set<Student> stus) {
        this.stus = stus;
    }
    public Teacher(int teaId, String teaName, Set<Student> stus) {
        this.teaId = teaId;
        this.teaName = teaName;
        this.stus = stus;
    }
    
    public Teacher(){
        
    }
}

在hibernate.cfg.xml最后添加映射关系：

<mapping resource="cn/hibernate/manytomany/teacher.hbm.xml"/>
<mapping resource="cn/hibernate/manytomany/student.hbm.xml"/>

teacher.hbm.xml和student.hbm.xml的代码为：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
    
    <hibernate-mapping>
        <class name="cn.hibernate.manytomany.Teacher" table="t_teacher">
            <id name="teaId" column="teaId">
                <generator class="native"></generator>
            </id>
            
            <property name="teaName" column="teaName" />
            
            <!-- student不放弃外键的维护 -->
            <set name="stus" table="t_tea_stu" cascade="all" inverse="false">
                <key column="teaId"></key>
                <many-to-many class="cn.hibernate.manytomany.Student" column="stuId"></many-to-many>
            </set>
        </class>
    </hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
    
    <hibernate-mapping>
        <class name="cn.hibernate.manytomany.Student" table="t_student">
            <id    name="stuId" column="stuId">
                <generator class="native"></generator>
            </id>
            
            <property name="stuName" column="stuName"></property>
            
            <!-- teacher放弃外键的维护 -->
            <set name="teachers" table="t_tea_stu" cascade="all" inverse="true">
                <key column="stuId"></key>
                <many-to-many class="cn.hibernate.manytomany.Teacher" column="teaId"></many-to-many>
            </set>
        </class>
    </hibernate-mapping>

MainFunc.java的代码为：

package cn.hibernate.manytomany;

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

public class MainFunc {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Configuration cfg = new Configuration().configure();
        SessionFactory sessionFactory = cfg.buildSessionFactory();
        Session session = sessionFactory.openSession();
        Transaction tx = null;
        try{
            tx = session.beginTransaction();
            
            Teacher tea1 = new Teacher();
            tea1.setTeaName("Zhangsan");
            Teacher tea2 = new Teacher();
            tea2.setTeaName("Lisi");
            
            Student stu1 = new Student();
            stu1.setStuName("Sheldon");
            Student stu2 = new Student();
            stu2.setStuName("Leonard");
            Student stu3 = new Student();
            stu3.setStuName("Howard");
            Student stu4 = new Student();
            stu4.setStuName("Raj");
            
            //把student和teacher关联
            stu1.getTeachers().add(tea1);
            stu1.getTeachers().add(tea2);
            stu2.getTeachers().add(tea1);
            stu2.getTeachers().add(tea2);
            stu3.getTeachers().add(tea1);
            stu4.getTeachers().add(tea2);
            
            //把teacher和student关联
            tea1.getStus().add(stu1);
            tea1.getStus().add(stu2);
            tea1.getStus().add(stu3);
            tea2.getStus().add(stu1);
            tea2.getStus().add(stu2);
            tea2.getStus().add(stu4);
            
            //由于teacher放弃了外键的维护，所以没有session.save(tea1/tea2)
            session.save(stu1);
            session.save(stu2);
            session.save(stu3);
            session.save(stu4);
            
            System.out.println("Add success");
            tx.commit();
        }catch(Exception e){
            e.printStackTrace();
            tx.rollback();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

}

最后，数据库中增加了t_teacher，t_student和中间表t_tea_stu

数据库内的数据为：

完成了Hibernate的多对多的级联映射。