标签：style class blog c code java
上篇文章讨论了双向关联的一对一映射，用了两个章节，主要是从主键和外键两种关联映射展开详细讨论，双向关联的映射需要在两个映射文件中分别添加相互的对应关系，斌刚在相应的类中添加对应的关联类的属性，这样在一端加载时才能加载到另一端的对象。关联中常用的主要有多对一、一对一、一对多和多对多，我们已经讨论了两种映射关系，接下来将会讨论一对多的关系。
<pre name="code" class="java">package com.src.hibernate;
import java.util.Set;
public class Classes {
private int id;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
private String name;
//Set支持延迟加载
private Set students;
public Set getStudents() {
return students;
}
public void setStudents(Set students) {
this.students = students;
}
}
Classes对象中使用了set属性，但是只是说明了延迟加载的属性，并没有为属性配置对应的对象，属性的对象是要在映射文件中来配置的，需要添加set标签，并在set标签中添加<one-to-many>标签，具体如下代码：<?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> <class name="com.hibernate.Classes" table="t_classes"> <id name="id"> <generator class="native"/> </id> <property name="name"/> <set name="students"> <key column="classesid"></key> <one-to-many class="com.hibernate.Student"></one-to-many> </set> </class> </hibernate-mapping>
alter table t_student drop foreign key FK4B9075705E0AFEFE drop table if exists t_classes drop table if exists t_student create table t_classes (id integer not null auto_increment, name varchar(255), primary key (id)) create table t_student (id integer not null auto_increment, name varchar(255), classesid integer, primary key (id)) alter table t_student add index FK4B9075705E0AFEFE (classesid), add constraint FK4B9075705E0AFEFE foreign key (classesid) references t_classes (id)
public void testSave2(){
Session session=null;
try{
session=HibernateUtils.getSession();
session.beginTransaction();
Student student1=new Student();
student1.setName("zhangsan");
session.save(student1);
Student student2=new Student();
student2.setName("lisi");
session.save(student2);
Classes classes=new Classes();
classes.setName("ClassOne");
Set students=new HashSet();
students.add(student1);
students.add(student2);
classes.setStudents(students);
//可以成功保存数据
//但是会发出多余的update语句来维持关系，因为是一对多的原因
session.save(classes);
session.getTransaction().commit();
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
HibernateUtils.closeSession(session);
}
}
package com.test.hibernate;
import java.util.Iterator;
import java.util.Set;
import com.src.hibernate.*;
import junit.framework.TestCase;
import org.hibernate.Session;
public class One2ManyTest extends TestCase {
public void testLoad1(){
Session session=null;
try{
session=HibernateUtils.getSession();
session.beginTransaction();
//获取主键为5的班级信息
Classes classes=(Classes)session.load(Classes.class,5);
//打印班级信息
System.out.println("classes.name="+classes.getName());
//设置学生集合，通过班级加载学生集合
Set students=classes.getStudents();
//迭代集合，打印集合中学生的信息
for(Iterator iter=students.iterator();iter.hasNext();){
Student student=(Student)iter.next();
System.out.println("student.name="+student.getName());
}
session.getTransaction().commit();
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
HibernateUtils.closeSession(session);
}
}
}
Hibernate: select classes0_.id as id1_0_, classes0_.name as name1_0_ from t_classes classes0_ where classes0_.id=? classes.name=ClassOne Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, students0_.id as id0_0_, students0_.name as name0_0_ from t_student students0_ where students0_.classesid=? student.name=lisi student.name=zhangsan
【Hibernate步步为营】--单向关联之一对多映射,布布扣,bubuko.com
标签：style class blog c code java
原文地址：http://blog.csdn.net/zhang_xinxiu/article/details/26761713
