hibernate--关联映射（一对多）

public class Classes {
    private int id;    
    private String name;
}

public class Student {
    private int id;    
    private String name;
    
    //一对多通常使用Set来映射，Set是不可重复内容。
    //注意使用Set这个接口，不要使用HashSet,因为hibernate有延迟加载，
    private Set students;
}

<?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 package="h.one.bean">
    <class name="Student" table="t_student">
        <id name="id" column="id">
            <generator class="native" />
        </id>
        <property name="name" column="name" />
    </class>
</hibernate-mapping>

<hibernate-mapping package="h.one.bean">
    <class name="Classes" table="t_classess">
        <id name="id" column="id">
            <generator class="native" />
        </id>
        <property name="name" column="name" />
        <!--<set>标签 映射一对多(映射set集合),name="属性集合名称"，然后在用<key>标签，在多的一端加入一个外键(column属性指定列名称)指向一的一端，再采用<one-to-many>标签说明一对多，还指定<set>标签中name="students"这个集合中的类型要使用完整的类路径(例如：class="com.wjt276.hibernate.Student") -->
        <set name="students">
            <key column="classesid" />
            <one-to-many class="com.wjt276.hibernate.Student" />
        </set>
    </class>
</hibernate-mapping>

session = HibernateUtil.getSession();
        tx = session.beginTransaction();

        Student student1 = new Student();
        student1.setName("10");
        session.save(student1);// 必需先存储，否则在保存classess时出错.

        Student student2 = new Student();
        student2.setName("祖儿");
        session.save(student2);// 必需先存储，否则在保存classess时出错.

        Set<Student> students = new HashSet<Student>();
        students.add(student1);
        students.add(student2);

        Classes classes = new Classes();
        classes.setName("wjt276");
        classes.setStudents(students);

        session.save(classes);

        // 提交事务
        tx.commit();

session = HibernateUtil.getSession();
        tx = session.beginTransaction();

        Classes classes = (Classes) session.load(Classes.class, 2);
        System.out.println("classes.name=" + classes.getName());
        Set<Student> students = classes.getStudents();
        for (Iterator<Student> iter = students.iterator(); iter.hasNext();) {
            Student student = iter.next();
            System.out.println(student.getName());
        }
        // 提交事务
        tx.commit();

session = HibernateUtils.getSession();
            tx = session.beginTransaction();
    
            Classes classes = new Classes();
            classes.setName("wjt168");
            session.save(classes);
            
            Student student1 = new Student();
            student1.setName("10");
            student1.setClasses(classes);
            session.save(student1);
            
            Student student2 = new Student();
            student2.setName("祖儿");
            student2.setClasses(classes);
            session.save(student2);
            
            //提交事务
            tx.commit();

<hibernate-mapping>
    <class name="h.one.bean.Classes" table="t_classes">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="name" column="name"/>
        
        <!--
            <set>标签 映射一对多(映射set集合),name="属性集合名称"
            然后在用<key>标签，在多的一端加入一个外键(column属性指定列名称)指向一的一端
            再采用<one-to-many>标签说明一对多，还指定<set>标签中name="students"这个集合中的类型
            要使用完整的类路径(例如：class="com.wjt276.hibernate.Student")
            inverse="false":一的一端维护关系失效(反转) ：false：可以从一的一端维护关系(默认)；true：从一的一端维护关系失效，这样如果在一的一端维护关系则不会发出Update语句。
         -->
        <set name="students" inverse="true">
            <key column="classesid"/>
            <one-to-many class="h.one.bean.Student"/>
        </set>
    </class>
</hibernate-mapping>

@Test
    public void testManyToMany(){
        session = HibernateUtil.getSession();
        tx = session.beginTransaction();

        Role r1 = new Role();
        r1.setName("数据录入人员");
        session.save(r1);
        
        Role r2 = new Role();
        r2.setName("商务主管");
        session.save(r2);
        
        Role r3 = new Role();
        r3.setName("大区经理");
        session.save(r3);
        
        Users u1 = new Users();
        u1.setName("10");
        Set<Role> u1Roles = new HashSet<Role>();
        u1Roles.add(r1);
        u1Roles.add(r2);
        u1.setRoles(u1Roles);
        
        Users u2 = new Users();
        u2.setName("祖儿");
        Set<Role> u2Roles = new HashSet<Role>();
        u2Roles.add(r2);
        u2Roles.add(r3);
        u2.setRoles(u2Roles);
        
        Users u3 = new Users();
        u3.setName("成龙");
        Set<Role> u3Roles = new HashSet<Role>();
        u3Roles.add(r1);
        u3Roles.add(r2);
        u3Roles.add(r3);
        u3.setRoles(u3Roles);
        

        session.save(u1);
        session.save(u2);
        session.save(u3);
        
        tx.commit();
    }

<hibernate-mapping>
    <class name="h.one.bean.Role" table="t_role">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="name"/>
        <!— order-by 属性是第三方表哪个字段进行排序-->
        <set name="users" table="t_user_role" order-by="userid">
            <key column="roleid"/>
            <many-to-many class="h.one.bean.Users" column="userid"/>
        </set>
    </class>
</hibernate-mapping>

session = HibernateUtil.getSession();
            tx = session.beginTransaction();
            
            Role role = (Role)session.load(Role.class, 1);
            System.out.println("role.name=" + role.getName());
            for (Iterator<UserS> iter = role.getUsers().iterator();iter.hasNext();){
                User user = iter.next();
                System.out.println("user.name=" + user.getName());
            }
            //提交事务
            tx.commit();