原文:http://www.open-open.com/doc/view/01ff044d600146079410e9968a1ddb86
Hibernate多对一单向关联(常用的关联模式)
类图:

表结构:

映射文件:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.User" table="t_user">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<!--
<many-to-one name="group" column="groupid" cascade="all"/>
-->
<many-to-one name="group" column="groupid"/>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Group" table="t_group">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
</class>
</hibernate-mapping>
hibernate多对一关联映射
关联映射的本质:
* 将关联关系映射到数据库,所谓的关联关系是对象模型在内存中的一个或多个引用
<many-to-one>会在多的一端加入一个外键,指向一的一端,这个外键是由<many-to-one>
中的column属性定义的,如果忽略了这个属性那么默认的外键与实体的属性一致
<many-to-one>标签的定义示例:
* <many-to-one name="group" column="groupid"/>
理解级联cascade的含义?
* 是对象的连锁操作(对增、删、改起作用)
相关测试:
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Group group = new Group();
group.setName("尚学堂");
User user1 = new User();
user1.setName("菜10");
user1.setGroup(group);
User user2 = new User();
user2.setName("容祖儿");
user2.setGroup(group);
//不能成功保存,抛出TransientObjectException异常
//因为Group为Tran sient状态,oid没有分配值
//persistent状态的对象是不能引用transient状态的对象的
session.save(user1);
session.save(user2);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Group group = new Group();
group.setName("尚学堂");
session.save(group);
User user1 = new User();
user1.setName("菜10");
user1.setGroup(group);
User user2 = new User();
user2.setName("容祖儿");
user2.setGroup(group);
//可以正确存储
session.save(user1);
session.save(user2);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave3() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Group group = new Group();
group.setName("尚学堂");
User user1 = new User();
user1.setName("菜10");
user1.setGroup(group);
User user2 = new User();
user2.setName("容祖儿");
user2.setGroup(group);
//不会抛出异常,因为采用了cascade属性,所以它会先保存Group
//采用cascade属性是解决TransientObjectException异常的一种手段
session.save(user1);
session.save(user2);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, 3);
System.out.println("user.name=" + user.getName());
System.out.println("user.group.name=" + user.getGroup().getName());//非常重要
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate一对一主键关联单向
类图:
数据表:
映射文件:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Person" table="t_person">
<id name="id">
<!-- person的主键来源idCard,也就是共享idCard的主键 -->
<generator class="foreign">
<param name="property">idCard</param>
</generator>
</id>
<property name="name"/>
<one-to-one name="idCard" constrained="true"/>(形成外键约束,很重要)
</class>
</hibernate-mapping>
理解one-to-one标签的含义:指示hibernate怎么加载它的关联对象,默认根据主键加载,constrained="true", 表明当前主键上存在一个约束,person的主键作为外键参照了idCard 。如果去掉constrained="true",那么就不会生成外键约束了。
<hibernate-mapping>
<class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
<id name="id">
<generator class="native"/>
</id>
<property name="cardNo"/>
</class>
</hibernate-mapping>
hibernate一对一主键关联映射(单向关联Person---->IdCard)
一对一主键关联映射:让两个实体对象的id保持相同,这样可以避免多余的字段被创建(如:t_person表中就省略了idCard字段这个外键)
相关测试:
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setCardNo("88888888888888");
Person person = new Person();
person.setName("菜10");
person.setIdCard(idCard);
//不会出现TransientObjectException异常
//因为一对一主键关联映射中,默认了cascade属性
session.save(person);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
//原理:把person查上来的主键拿到,然后到t_idCard这张表,比较idCard主键和它相等,把它加载下来,把它放到person的属性idCard里。
Person person = (Person)session.load(Person.class, 1);
System.out.println("person.name=" + person.getName());
System.out.println("idCard.cardNo=" + person.getIdCard().getCardNo());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate一对一主键关联双向
类图:
表结构(跟主键单向关联的一样):
映射文件:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Person" table="t_person">
<id name="id">
<generator class="foreign">
<param name="property">idCard</param>
</generator>
</id>
<property name="name"/>
<one-to-one name="idCard" constrained="true"/>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
<id name="id">
<generator class="native"/>
</id>
<property name="cardNo"/>
<one-to-one name="person"/>(此标签用来在IdCard一端加载person对象)
</class>
</hibernate-mapping>
说明:
hibernate一对一主键关联映射(双向关联Person<---->IdCard)
需要在idcard映射文件中加入<one-to-one>标签指向person,指示hibernate如何加载person,默认根据主键加载。
相关测试:
public void testLoad2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = (IdCard)session.load(IdCard.class, 1);
System.out.println("idcard.cardNo=" + idCard.getCardNo());
System.out.println("idcard.person.name=" + idCard.getPerson().getName());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate一对一唯一外键关联单向
类图:
表结构(注意:在t_person表中增加了idCard字段):

相关映射:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Person" table="t_person">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<many-to-one name="idCard" unique="true"/>
</class>
</hibernate-mapping>
说明:
hibernate一对一唯一外键关联映射(单向关联Person---->IdCard)
一对唯一外键关联映射是多对一关联映射的特例
可以采用<many-to-one>标签,指定多的一端的unique=true,这样就限制了多的一端的多重性为一,通过这种手段映射一对一唯一外键关联
<hibernate-mapping>
<class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
<id name="id">
<generator class="native"/>
</id>
<property name="cardNo"/>
</class>
</hibernate-mapping>
相关测试:
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setCardNo("88888888888888");
Person person = new Person();
person.setName("菜10");
person.setIdCard(idCard);
//不能成功保存,因为IdCard是Transient状态
session.save(person);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setCardNo("88888888888888");
session.save(idCard);
Person person = new Person();
person.setName("菜10");
person.setIdCard(idCard);
session.save(person);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Person person = (Person)session.load(Person.class, 2);
System.out.println("person.name=" + person.getName());
System.out.println("idCard.cardNo=" + person.getIdCard().getCardNo());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate一对一唯一外键关联双向
类图:
表结构:
相关映射:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Person" table="t_person">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<many-to-one name="idCard" unique="true"/>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
<id name="id">
<generator class="native"/>
</id>
<property name="cardNo"/>
<one-to-one name="person" property-ref="idCard"/>
</class>
</hibernate-mapping>
说明:
hibernate一对一唯一外键关联映射(双向关联Person<---->IdCard)
一对一唯一外键关联双向,需要在另一端(idcard),添加<one-to-one>标签,指示hibernate如何加载,其关联对象,默认根据主键加载person,外键关联映射中,因为两个实体采用的是person的外键维护的关系,所以不能指定主键加载person,而要根据person的外键加载,所以采用如下映射方式:
<one-to-one name="person" property-ref="idCard"/>
相关测试:
public void testLoad2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = (IdCard)session.load(IdCard.class, 1);
System.out.println("idcard.cardNo=" + idCard.getCardNo());
System.out.println("idcard.person.name=" + idCard.getPerson().getName());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate一对多单向关联
类图:
表结构:

相关映射:
<hibernate-mapping>
<class name=" com.bjsxt.hibernate .Classes" table="t_classes">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="students">
<key column="classesid"/>
<one-to-many class="com.bjsxt.hibernate.Student"/>
</set>
</class>
</hibernate-mapping>
注:因为在Class的类中有个属性Set,但是不知道Set里面放的是什么类型的东西,所以在配置映射文件的时候通过标签<one-to-many class="com.bjsxt.hibernate.Student"/>来指定Set中元素的类型。
理解<key column="classesid"/>标签的作用:在t_student表中增加了一个列classid作为外键(foreign key),参照了t_calss表的主键id。
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Student" table="t_student">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
</class>
</hibernate-mapping>
说明:
hihernate一对多关联映射(单向Classes----->Student)
一对多关联映射利用了多对一关联映射原理
多对一关联映射:在多的一端加入一个外键指向一的一端,它维护的关系是多指向一
一对多关联映射:在多的一端加入一个外键指向一的一端,它维护的关系是一指向多
也就是说一对多和多对一的映射策略是一样的,只是站的角度不同
在一的一端维护关系的缺点:
* 如果将t_student表里的classesid字段(外键)设置为非空,则无法保存
* 因为不是在student这一端维护关系,所以student不知道是哪个班的,
所以需要发出多余的update语句来更新关系
相关测试:
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Student student1 = new Student();
student1.setName("10");
session.save(student1);
Student student2 = new Student();
student2.setName("祖儿");
session.save(student2);
Set students = new HashSet();
students.add(student1);
students.add(student2);
Classes classes = new Classes();
classes.setName("尚学堂");
classes.setStudents(students);
//可以正确保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Classes classes = (Classes)session.load(Classes.class, 1);
System.out.println("classes.name=" + classes.getName());
Set students = classes.getStudents();
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一对多双向关联
类图:
表结构:

<hibernate-mapping package="com.bjsxt.hibernate">
<class name="Classes" table="t_classes">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="students" inverse="true" cascade="all">
<key column="classesid"/>
<one-to-many class="Student"/>
</set>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Student" table="t_student">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<many-to-one name="classes" column="classesid"/>
</class>
</hibernate-mapping>
注:______的部分必须是一样的
说明:
hihernate一对多关联映射(双向Classes<----->Student)
一对多双向关联映射:
* 在一的一端的集合上使用<key>,在对方表中加入一个外键指向一一端
* 在多一端采用<many-to-one>
注意:<key>标签指定的外键字段必须和<many-to-one>指定的外键字段一致,否则引用字段的错误
如果在一的一端维护一对多关联关系,hibernate会发出多余的udpate语句,所以我们一般在多的一端来维护关联关系
关于inverse属性:
inverse主要用在一对多和多对多双向关联上,inverse可以被设置到集合标签<set>上,
默认inverse为false,所以我们可以从一的一端和多的一端维护关联关系,
如果设置成inverse为true,则我们只能从多一端来维护关联关系
注意:inverse属性,只影响数据的存储,也就是持久化
inverse和cascade
* inverse是关联关系的控制方向
* cascade操作上的连锁反应
相关测试:
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Student student1 = new Student();
student1.setName("10");
session.save(student1);
Student student2 = new Student();
student2.setName("祖儿");
session.save(student2);
Set students = new HashSet();
students.add(student1);
students.add(student2);
Classes classes = new Classes();
classes.setName("尚学堂");
classes.setStudents(students);
//可以正确保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave2() {//常用的方法
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Classes classes = new Classes();
classes.setName("尚学堂");
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);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave3() {//用到cascade属性,自动级联。
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Classes classes = new Classes();
classes.setName("尚学堂");
Student student1 = new Student();
student1.setName("10");
student1.setClasses(classes);
Student student2 = new Student();
student2.setName("祖儿");
student2.setClasses(classes);
Set students = new HashSet();
students.add(student1);
students.add(student2);
classes.setStudents(students);
//可以正确保存
session.save(classes);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Classes classes = (Classes)session.load(Classes.class, 1);
System.out.println("classes.name=" + classes.getName());
Set students = classes.getStudents();
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);
}
}
public void testLoad2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Student student = (Student)session.load(Student.class, 1);
System.out.println("student.name=" + student.getName());
System.out.println("student.classes.name=" + student.getClasses().getName());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate多对多单向关联
类图:
表结构:

注:table="t_user_role"指明第三方表的名字为t_user_roles,key column="userid"指明其中的一列(作为外键关联到表t_user的主键id),column="roleid"指明其中的另一列(作为外键关联到表t_role的主键id)。
在设计数据库表t_user_role时把(userid,roleid)设置为联合主键。
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Role" table="t_role">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
</class>
</hibernate-mapping>
相关测试:
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
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);
User u1 = new User();
u1.setName("10");
Set u1Roles = new HashSet();
u1Roles.add(r1);
u1Roles.add(r2);
u1.setRoles(u1Roles);
User u2 = new User();
u2.setName("祖儿");
Set u2Roles = new HashSet();
u2Roles.add(r2);
u2Roles.add(r3);
u2.setRoles(u2Roles);
User u3 = new User();
u3.setName("杰伦");
Set u3Roles = new HashSet();
u3Roles.add(r1);
u3Roles.add(r2);
u3Roles.add(r3);
u3.setRoles(u3Roles);
session.save(u1);
session.save(u2);
session.save(u3);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, 1);
System.out.println(user.getName());
for (Iterator iter=user.getRoles().iterator(); iter.hasNext();) {
Role role = (Role)iter.next();
System.out.println(role.getName());
}
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
Hibernate多对多双向关联
类图:
表结构:

相关映射:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.User" table="t_user">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="roles" table="t_user_role">
<key column="userid"/>
<many-to-many class="com.bjsxt.hibernate.Role" column="roleid"/>
</set>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Role" table="t_role">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="users" table="t_user_role" order-by="userid">
<key column="roleid"/>
<many-to-many class="com.bjsxt.hibernate.User" column="userid"/>
</set>
</class>
</hibernate-mapping>
说明:
hibernate多对多关联映射(双向User<---->Role)
映射方法:
table属性值必须和单向关联中的table属性值一致
<key>中column属性值要与单向关联中的<many-to-many>标签中的column属性值一致
在<many-to-many>中的column属性值要与单向关联中<key>标签的column属性值一致
相关测试:
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
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);
User u1 = new User();
u1.setName("10");
Set u1Roles = new HashSet();
u1Roles.add(r1);
u1Roles.add(r2);
u1.setRoles(u1Roles);
User u2 = new User();
u2.setName("祖儿");
Set u2Roles = new HashSet();
u2Roles.add(r2);
u2Roles.add(r3);
u2.setRoles(u2Roles);
User u3 = new User();
u3.setName("杰伦");
Set u3Roles = new HashSet();
u3Roles.add(r1);
u3Roles.add(r2);
u3Roles.add(r3);
u3.setRoles(u3Roles);
session.save(u1);
session.save(u2);
session.save(u3);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.load(User.class, 1);
System.out.println(user.getName());
for (Iterator iter=user.getRoles().iterator(); iter.hasNext();) {
Role role = (Role)iter.next();
System.out.println(role.getName());
}
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Role role = (Role)session.load(Role.class, 1);
System.out.println(role.getName());
for (Iterator iter=role.getUsers().iterator(); iter.hasNext();) {
User user = (User)iter.next();
System.out.println(user.getName());
}
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}