Hibernate 学习笔记/代码(双向一对多)

先来张代码结构图



先是实体类

Student

package com.hibernate.entity;

public class Student {

private int sid;
public int getSid() {
return sid;
}

public void setSid(int sid) {
this.sid = sid;
}

private String sname;
private String sex;

//在多方定义一个 一方的引用
private Grade grade;

public String getSname() {
return sname;
}

public void setSname(String sname) {
this.sname = sname;
}

public String getSex() {
return sex;
}

public void setSex(String sex) {
this.sex = sex;
}

public Student() {
// super();
}

public Student(String sname, String sex) {
// super();
this.sname = sname;
this.sex = sex;
}

@Override
public String toString() {
return "Student [sid=" + sid + ", sname=" + sname + ", sex=" + sex
+ ", grade=" + grade + "]";
}

public Grade getGrade() {
return grade;
}

public void setGrade(Grade grade) {
this.grade = grade;
}
}
Grade类
package com.hibernate.entity;

import java.util.HashSet;
import java.util.Set;

public class Grade {

private int gid;
private String gname;
private String gdesc;

private Set<Student> student = new HashSet<Student>();

public Set<Student> getStudent() {
return student;
}

public void setStudent(Set<Student> student) {
this.student = student;
}

public int getGid() {
return gid;
}

public void setGid(int gid) {
this.gid = gid;
}

public String getGname() {
return gname;
}

public void setGname(String gname) {
this.gname = gname;
}

public String getGdesc() {
return gdesc;
}

public void setGdesc(String gdesc) {
this.gdesc = gdesc;
}

@Override
public String toString() {
return "Grade [gid=" + gid + ", gname=" + gname + ", gdesc=" + gdesc
+ "]";
}

public Grade(String gname, String gdesc) {
// super();
this.gname = gname;
this.gdesc = gdesc;
}

public Grade() {
// super();
}
}


hibernate 实体类的配置文件
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<!-- 班级对象关系映射 -->
<hibernate-mapping>
<class name="com.hibernate.entity.Grade" table="grade" >
<id name="gid" type="integer" column="gid">
<generator class="increment"/>
</id>
<property name="gname" type="string" column="gname" not-null="true" length="20"></property>
<property name="gdesc" column="gdesc"></property>

<!-- 设置inverse属性为true,由多方维护关联关系 当进行保存和更新时,自动进行级联的操作 -->
<set name="student" table="student" inverse="true" cascade="save-update">
<key column="gid"></key>
<one-to-many class="com.hibernate.entity.Student"/>
</set>

<!--
cascade属性
当设置了cascade属性不为none时,Hibernate会自动持久化所关联的对象
cascade属性的设置会带来性能上的变动,需谨慎!
属性:
all : 对所有操作进行级联操作
save-update:执行保存和更新操作时进行级联操作
delete:执行删除操作时,进行级联操作
nono:对所有操作不进行级联操作
-->

<!--
<Set>节点的inverse属性指定关联关系的控制方向,默认由one方来维护
关联关系中,inverse = false,则为主动方,由主动方负责维护关联关系
在一对多关联中,只能设置one方的inverse为true,这将有助于性能的改善
-->

</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<!-- 学生的对象关系映射 -->
<hibernate-mapping>
<class name="com.hibernate.entity.Student"  table="student">
<id name="sid" type="int" column="sid">
<generator class="increment"/>
</id>
<property name="sname" type="java.lang.String" column="sname" length="20" not-null="true"></property>
<property name="sex" type="java.lang.String" column="sex"></property>

<!-- 配置多对一关联关系 name:就是实体类中引用的属性名称-->
<many-to-one name="grade" class="com.hibernate.entity.Grade" column="gid" cascade="all"></many-to-one>

</class>

</hibernate-mapping>

hibernate主配置文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.username">root</property> <!-- 数据库用户名 -->
<property name="connection.password">1234</property> <!-- 数据库密码 -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property><!-- 数据库驱动 -->
<!-- 数据库地址 -->
<property name="connection.url">jdbc:mysql://localhost:3306/test?user=root&password=1234&useUnicode=true&characterEncoding=UTF-8</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property><!-- mysql 数据库方言 -->

<property name="show_sql">true</property>
<property name="format_sql">false</property>
<property name="hbm2ddl.auto">update</property>

<mapping resource="com/hibernate/entity/Grade.hbm.xml"/>
<mapping resource="com/hibernate/entity/Student.hbm.xml"/>

</session-factory>
</hibernate-configuration>


GetSession 工具类

package com.hibernate.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;

public class HibernateUtil {
private static SessionFactory sessionFactory;
private static Session session;

static{
//创建配置对象
Configuration config = new Configuration().configure();
//创建服务注册对象
ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
//创建会话工厂对象
sessionFactory = config.buildSessionFactory(serviceRegistry);
//创建会话对象
session = sessionFactory.openSession();
}

//获取sessionFactory
public static SessionFactory getSessionFactory(){
return sessionFactory;
}

//获取session
public static Session getSession(){
session = sessionFactory.openSession();
return session;
}

//关闭session
public static void closeSession(Session session){
if(session != null){
session.close();
}
}

}


测试代码:
package com.hibernate.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import com.hibernate.entity.Grade;
import com.hibernate.entity.Student;
import com.hibernate.util.HibernateUtil;

/**
* 单向多对一
* 学生--> 班级
*
* 实际上已建立了双向的一对多,也称为双向多对一
* 即可以方便的由学生查找到对应的班级信息,也可以方便的由班级查找到其所包含的学生信息
* @author cyx
*
*/
public class TestManyToOne {
private Session session;
private Transaction transaction;
private HibernateUtil hibernateUtil;

/**
* 双向
*/
@Test
public void save(){
try{
session = hibernateUtil.getSession();
transaction = session.beginTransaction();

Grade grade = new Grade("JavaScript一班","软件开发");
Student stu1 = new Student("小小","女");
Student stu2 = new Student("大大","男");

//设置关联
grade.getStudent().add(stu1);
grade.getStudent().add(stu2);
stu1.setGrade(grade);
stu2.setGrade(grade);

session.save(grade);
//保存班级时候,班级中有学生,并且学生不存在于数据库,自动将学生保存到数据库中
//保存班级的时候,班级就已经有了学生的信息,还要讲学生信息在保存一遍会很麻烦..
//可以使用级联的操作
// session.save(stu1);
// session.save(stu2);

transaction.commit();
}catch(Exception e){
e.printStackTrace();
transaction.rollback();
}finally{
if(session != null){
hibernateUtil.closeSession(session);
}
}
}

@Test
public void findGroudByStudent(){
try{

session = hibernateUtil.getSession();

Student student = (Student)session.get(Student.class, 1);
System.out.println(student.getSid()+","+student.getSname()+","+student.getSex());;

Grade grade = student.getGrade();
System.out.println(grade.getGid()+","+grade.getGname()+","+grade.getGdesc());

}catch(Exception e){
e.printStackTrace();
}
}
}