班级的映射关系表
<?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>
<class name="cn.itcast.domain.Classess">
<id name="cid" length="5" type="java.lang.Long">
<generator class="increment"></generator>
</id>
<property name="cname" length="20" type="java.lang.String"></property>
<property name="description" length="100" type="java.lang.String"></property>
<!--
set元素对应类中的set集合
通过set元素使classes表与student表建立关联
key是通过外键的形式让两张表建立关联
one-to-many是通过类的形式让两个类建立关联
cascade 级联
save-update
1、当 保存班级的时候，对学生进行怎么样的操作
如果学生对象在数据库中没有对应的值，这个时候会执行save操作
如果学生对象在数据库中有对应的值，这个时候会执行update操作
delete
all
inverse 维护关系
true 不维护关系
false 维护关系
default false
-->
<set name="students" cascade="all" inverse="true">
<!-- key是用来描述外键-->
<key>
<column name="cid"></column>
</key>
<one-to-many class="cn.itcast.domain.Student"/>
</set>
</class>
</hibernate-mapping>
学生映射关系表
<?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>
<class name="cn.itcast.domain.Student">
<id name="sid" length="5">
<generator class="increment"></generator>
</id>
<property name="sname" length="20"></property>
<property name="description" length="100"></property>
</class>
</hibernate-mapping>
1.保存班级和学生
@Test
public void testSaveClassess(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = new Classess();
Classess.setCname("传智上海云一期");
Classess.setDescription("很牛");
session.save(Classess);
transaction.commit();
session.close();
}
@Test
public void testSaveStudent(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = new Student();
student.setSname("班长");
student.setDescription("老牛：很牛");
session.save(student);
transaction.commit();
session.close();
}
@Test
public void testSaveClassess_Student(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = new Classess();
Classess.setCname("xxx:");
Classess.setDescription("很牛X");
Student student = new Student();
student.setSname("班长");
student.setDescription("老牛：很牛X");
session.save(student);
session.save(Classess);
transaction.commit();
session.close();
}
2.cascade-1-保存班级保存学生
1、在classes.hbm.xml文件，针对student进行了级联操作save-update
2、在客户端的代码中，通过班级建立班级与学生之间的关系
3、因为student是一个临时状态的对象
4、在保存班级的时候同时保存学生
/**
* 在保存班级的时候，级联保存学生
*/
@Test
public void testSaveClassess_Cascade_Student_Save(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = new Classess();
Classess.setCname("xxxxxxxxx2:");
Classess.setDescription("很牛XX");
Student student = new Student();
student.setSname("班长");
student.setDescription("老牛：很牛XX");
Set<Student> students = new HashSet<Student>();
students.add(student);
//建立Classess与student之间的关联
Classess.setStudents(students);
session.save(Classess);
transaction.commit();
session.close();
}
@Test
public void testSaveClassess_Cascade_Student_Update(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = new Classess();
Classess.setCname("xxxxxxxx4:");
Classess.setDescription("很牛XXX");
Student student = (Student)session.get(Student.class, 1L);
student.setSname("班秘");
Set<Student> students = new HashSet<Student>();
students.add(student);
Classess.setStudents(students);
session.save(Classess);
transaction.commit();
session.close();
}
@Test
public void testUpdateClassess_Cascade_Student_Save(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = (Classess)session.get(Classess.class, 5L);
Student student = new Student();
student.setSname("班花");
student.setDescription("稀有人物");
Classess.getStudents().add(student);
transaction.commit();
session.close();
}
3.cascade-2-保存班级更新学生
@Test
public void testUpdateClassess_Cascade_Student_Update(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = (Classess)session.get(Classess.class, 5L);
Set<Student> students = Classess.getStudents();//为cid为5的班级的所有的学生
//for(Student student:students){
//student.setDescription("压力山大");
//}
transaction.commit();
session.close();
}
4.更新班级保存或者更新学生-隐式操作异常
在客户端试图通过保存班级保存学生，但是由于在配置文件中针对students没有cascade属性，没有级联，所以导致
classes中的student成为临时状态的对象了，hibernate不允许这种情况出现
把session.save/update一个对象的操作为显示操作，级联对象的操作为隐式操作
/**
* 一个错误的演示,映射文件中没有写级联属性
*/
@Test
public void testSaveClassess_Cascade_Student_Save_Error(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = new Classess();
Classess.setCname("xxxxxxxx5:");
Classess.setDescription("很牛XXXXXX");
Student student = new Student();
student.setSname("班长XXXXXX");
student.setDescription("老牛：很牛XXXXXX");
Set<Student> students = new HashSet<Student>();
students.add(student);
//建立Classess与student之间的关联
Classess.setStudents(students);
session.save(Classess);
transaction.commit();
session.close();
}
5-关系操作 inverse
Classes.hbm.xml
<set name="students" inverse="true/false/default">
inverse所在的映射文件classes对classes与student之间的关系是否进行维护
维护关系体现在两点：
1、在映射文件中inverse的值必须是false/default
2、必须在客户端代码上建立两者之间的关系
/**
* 已经存在一个班级，新建一个学生，建立学生与班级之间的关系
* 通过更新班级级联保存学生 cascade
* 建立班级和学生之间的关系 inverse
*/
@Test
public void testSaveStudent_R_1(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = new Student();
student.setSname("技术班长");
student.setDescription("大神");
Classess Classess = (Classess)session.get(Classess.class, 1L);
Classess.getStudents().add(student);
transaction.commit();
session.close();
}
/**
* Hibernate: select Classess0_.cid as cid0_0_, Classess0_.cname as cname0_0_, Classess0_.description as descript3_0_0_ from Classess Classess0_ where Classess0_.cid=?
Hibernate: select max(sid) from Student
Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_, students0_.sid as sid1_0_, students0_.sname as sname1_0_, students0_.description as descript3_1_0_ from Student students0_ where students0_.cid=?
Hibernate: insert into Student (sname, description, sid) values (?, ?, ?)
更新关系的操作
Hibernate: update Student set cid=? where sid=?
*/
@Test
public void testSaveStudent_R_2(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = new Student();
student.setSname("技术班长");
student.setDescription("大神");
Classess Classess = (Classess)session.get(Classess.class, 1L);
session.save(student);
Classess.getStudents().add(student);
transaction.commit();
session.close();
}
/**
* 已经存在一个学生，新建一个班级，把学生加入到该班级
*/
@Test
public void testSaveClassess_R(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = new Classess();
Classess.setCname("老毕基础加强班");
Classess.setDescription("必看，杀手锏");
Student student = (Student)session.get(Student.class, 2L);
Set<Student> students = new HashSet<Student>();
students.add(student);
Classess.setStudents(students);
session.save(Classess);
transaction.commit();
session.close();
}
/**
* 把一个学生从一个班级转移到另一个班级
* Hibernate: select Classess0_.cid as cid0_0_, Classess0_.cname as cname0_0_, Classess0_.description as descript3_0_0_ from Classess Classess0_ where Classess0_.cid=?
Hibernate: select Classess0_.cid as cid0_0_, Classess0_.cname as cname0_0_, Classess0_.description as descript3_0_0_ from Classess Classess0_ where Classess0_.cid=?
Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_, student0_.description as descript3_1_0_ from Student student0_ where student0_.sid=?
Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_, students0_.sid as sid1_0_, students0_.sname as sname1_0_, students0_.description as descript3_1_0_ from Student students0_ where students0_.cid=?
Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_, students0_.sid as sid1_0_, students0_.sname as sname1_0_, students0_.description as descript3_1_0_ from Student students0_ where students0_.cid=?
Hibernate: update Student set cid=null where cid=? and sid=?
Hibernate: update Student set cid=? where sid=?
*/
@Test
public void testTransformClass(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
//Classess Classess5 = (Classess)session.get(Classess.class, 5L);
Classess Classess6 = (Classess)session.get(Classess.class, 6L);
Student student = (Student)session.get(Student.class, 1L);
//Classess5.getStudents().remove(student);
Classess6.getStudents().add(student);
transaction.commit();
session.close();
}
/**
* 解除一个班级和一些学生之间的关系
*/
@Test
public void testR_Some(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = (Classess)session.get(Classess.class, 1L);
Set<Student> students = Classess.getStudents();
//for(Student student:students){
//if(student.getSid().longValue()==6||student.getSid().longValue()==7){
//students.remove(student);
//}
//}
//set-->list
//List<Student> sList = new ArrayList<Student>(students);
//for(int i=0;i<sList.size();i++){
// if(sList.get(i).getSid().longValue()==6||sList.get(i).getSid().longValue()==7){
// sList.remove(sList.get(i));
// i--;
//}
//}
students = new HashSet<Student>(sList);
Classess.setStudents(students);
/**
* 增强for循环只能修改一次
* 1、用普通的for循环
* 2、新建一个set集合，把原来的set集合要保留的数据存放到新的set集合中
*/
transaction.commit();
session.close();
}
/*
* Classess.setStudents(null);直接把班级针对student的集合设置为null
*/
@Test
public void testRealseAll(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Classess Classess = (Classess)session.get(Classess.class, 1L);
//Set<Student> students = Classess.getStudents();
//students.clear();
Classess.setStudents(null);
transaction.commit();
session.close();
}
/**
* 已经存在一个班级，已经存在一个学生，建立该班级与该学生之间的关系
* 11、已经存在一个班级，已经存在多个学生，建立多个学生与班级之间的关系
*/
//cascade=”delete”或”all”
@Test
public void testDeleteStudent(){
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Student student = (Student)session.get(Student.class, 8L);
session.delete(student);
transaction.commit();
session.close();
}原文：http://pengya123.blog.51cto.com/8467424/1811624