Hibernate_OneToMany_Demo

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="org.zttc.itat.model">    <class name="Message" table="t_msg">        <id name="id">        <!-- 表示不会自动生成，而是需要由用户来指定 -->          <!--   <generator class="assigned"/> -->        <!-- 会自动生成一个字符串，此时组件必须为String类型 -->          <generator class="native"/>        </id>        <property name="title"/>        <property name="content"/>        <!-- 使用了lazy=extra之后会稍微智能一些，会根据去的值的不同来判断是调用count和获取投影 -->        <set name="comments" lazy="extra">        <!-- key用来指定在对方的外键的名称 -->        <key column="mid"/>        <!-- class用来设置列表中的对象类型 -->        <one-to-many class="Comment"/>        </set>    </class></hibernate-mapping>

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="org.zttc.itat.model">    <class name="Classroom" table="t_cla">        <id name="id">        <!-- 表示不会自动生成，而是需要由用户来指定 -->          <!--   <generator class="assigned"/> -->        <!-- 会自动生成一个字符串，此时组件必须为String类型 -->          <generator class="native"/>        </id>        <property name="name"/>        <property name="grade"/>        <!-- inverse=true表示不再自己这一端维护关系 -->        <set name="stus" lazy="extra" inverse="true">        <key column="cid"/>        <one-to-many class="Student"/>        </set>    </class></hibernate-mapping>

package org.zttc.itat.test;import java.util.HashSet;import java.util.Set;import org.hibernate.Session;import org.junit.Test;import org.zttc.itat.model.Classroom;import org.zttc.itat.model.Comment;import org.zttc.itat.model.Message;import org.zttc.itat.model.Student;import org.zttc.itat.util.HibernateUtil;public class TestOne2Many {@Testpublic void testAdd() {Session session = null;try {session = HibernateUtil.openSession();session.beginTransaction();Comment c1 = new Comment();c1.setContent("123123123");Comment c2 = new Comment();c2.setContent("1sdsfdfsdf");session.save(c1); session.save(c2);Message msg = new Message();msg.setTitle("sdfsdfsdfsdf");msg.setContent("sdfsdfsdfsdf");msg.addComment(c1);msg.addComment(c2);session.save(msg);//此时会发出5条sql，三条查询，两条更新session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();if(session!=null) session.getTransaction().rollback();} finally {HibernateUtil.close(session);}}@Testpublic void testLoad() {Session session = null;try {session = HibernateUtil.openSession();session.beginTransaction();Message msg = (Message)session.load(Message.class, 1);System.out.println(msg.getContent());for(Comment comment:msg.getComments()) {System.out.println(comment.getContent());}session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();if(session!=null) session.getTransaction().rollback();} finally {HibernateUtil.close(session);}}@Testpublic void testLoad2() {Session session = null;try {session = HibernateUtil.openSession();session.beginTransaction();Message msg = (Message)session.load(Message.class, 1);System.out.println(msg.getComments().size());session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();if(session!=null) session.getTransaction().rollback();} finally {HibernateUtil.close(session);}}//特别注意，oneToMany在添加和维护关系时比较麻烦，所以在开发中不建议使用OneToMany的单向@Testpublic void testAdd01() {Session session = null;try {session = HibernateUtil.openSession();session.beginTransaction();Student stu1 = new Student();stu1.setName("猪八戒");stu1.setNo("1111");session.save(stu1);Student stu2 = new Student();stu2.setName("朱纠结");stu2.setNo("2222");session.save(stu2);Classroom cla = new Classroom();cla.setGrade(2012);cla.setName("计算机应用技术");Set<Student> stus = new HashSet<Student>();stus.add(stu1); stus.add(stu2);cla.setStus(stus);session.save(cla);/* * 此时也会发出5条sql，所以最佳实践就是不要使用1的一方来维护关系 * 在配置文件的set标签中可以通过inverse=true来明确不使用一的这一端维护关系 */session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();if(session!=null) session.getTransaction().rollback();} finally {HibernateUtil.close(session);}}@Testpublic void testAdd02() {Session session = null;try {session = HibernateUtil.openSession();session.beginTransaction();Classroom cla = new Classroom();cla.setGrade(2012);cla.setName("计算机网络技术");session.save(cla);Student stu1 = new Student();stu1.setName("猪八戒");stu1.setNo("1111");stu1.setClassroom(cla);session.save(stu1);Student stu2 = new Student();stu2.setName("朱纠结");stu2.setNo("2222");stu2.setClassroom(cla);session.save(stu2);session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();if(session!=null) session.getTransaction().rollback();} finally {HibernateUtil.close(session);}}      /**       * 下文如果注释部分没有注释，则会发出一条sql取班级，然后再发一条sql统计大小（由于延迟加载，必须取一个id以外数据，此处统计大小只是演示），       *最后只需要再发一条sql取学生；虽然有延迟加载，但是这个学生所在的班级已经在之前取出来放缓存中了，所以stu.getClassroom().getGrade()，就不用再加载了       */        @Testpublic void testLoad02() {Session session = null;try {session = HibernateUtil.openSession();session.beginTransaction();//Classroom cla = (Classroom)session.load(Classroom.class, 6);//System.out.println(cla.getStus().size());Student stu = (Student)session.load(Student.class, 15);  System.out.println(stu.getName()+","+stu.getClassroom().getGrade());session.getTransaction().commit();} catch (Exception e) {e.printStackTrace();if(session!=null) session.getTransaction().rollback();} finally {HibernateUtil.close(session);}}}