组件的映射
建立关系数据模型的一个重要原则是在不会导致数据冗余的前提下，尽可能减少数据库表中的数目及表之间的外键参照关系。以员工信息为例，员工信息中有员工的家庭地址信息，如果把地址信息单独放在一张表中，然后建立员工信息表和地址信息表之间的外键关系，当每次查询员工信息时，都需要建立这两个表的连接。建立表的连接是很耗时的操作，为了提高数据库运行性能，可以把这两张表的信息整合在一张员工信息表Empinfo中
提示：
HibernateUtil工具类（用于获取session和关闭session）
package cn.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
//初始化一个ThreadLocal对象，有get和set方法
private static final ThreadLocal<Session> sessionTL=new ThreadLocal<Session>();
private static Configuration configuration;
private final static SessionFactory sessionFactory;
static{
configuration=new Configuration().configure();
sessionFactory=configuration.buildSessionFactory();
}
//获得session对象
public static Session currentSession() {
//sessionTL的get方法根据当前线程返回其对应的线程内部变量，即Session对象，多线程情况下共享数据库连接是不安全的。
//ThreadLocal保证了每个线程都有自己的session对象
Session session=(Session)sessionTL.get();
if (session==null) {
session=sessionFactory.openSession();
sessionTL.set(session);
}
return session;
}
//关闭session对象
public static void closeSession() {
Session session=(Session)sessionTL.get();
sessionTL.set(null);
session.close();
}
}
EmpHomeAddress实体类：
package cn.entity;
/*
* 地址信息类
*/
public class EmpHomeAddress {
private String ehomestreet;
private String ehomecity;
private String ehomeprovince;
private String ehomezipcode;
private EmpInfo empinfo;
public String getEhomestreet() {
return ehomestreet;
}
public void setEhomestreet(String ehomestreet) {
this.ehomestreet = ehomestreet;
}
public String getEhomecity() {
return ehomecity;
}
public void setEhomecity(String ehomecity) {
this.ehomecity = ehomecity;
}
public String getEhomeprovince() {
return ehomeprovince;
}
public void setEhomeprovince(String ehomeprovince) {
this.ehomeprovince = ehomeprovince;
}
public String getEhomezipcode() {
return ehomezipcode;
}
public void setEhomezipcode(String ehomezipcode) {
this.ehomezipcode = ehomezipcode;
}
public EmpInfo getEmpinfo() {
return empinfo;
}
public void setEmpinfo(EmpInfo empinfo) {
this.empinfo = empinfo;
}
}
EmpInfo实体类：
package cn.entity;
/*
* 员工类
*/
public class EmpInfo {
private Integer eid;
private String ename;
private EmpHomeAddress ehome;
public Integer getEid() {
return eid;
}
public void setEid(Integer eid) {
this.eid = eid;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public EmpHomeAddress getEhome() {
return ehome;
}
public void setEhome(EmpHomeAddress ehome) {
this.ehome = ehome;
}
}
EmpInfo.hbm.xml映射文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.entity">
<class name="EmpInfo" table="empinfo">
<id name="eid" column="eid">
<generator class="native"></generator>
</id>
<property name="ename" column="ENAME" type="string"></property>
<component name="ehome" class="EmpHomeAddress">
<parent name="empinfo"/>
<property name="ehomestreet" column="EHOMESTREET" type="string"></property>
<property name="ehomecity" column="EHOMECITY" type="string"></property>
<property name="ehomeprovince" column="EHOMEPROVINCE" type="string"></property>
<property name="ehomezipcode" column="EHOMEZIPCODE" type="string"></property>
</component>
</class>
</hibernate-mapping>
hibernate.cfg.xml大配置文件:
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings 数据库连接设置-->
<!-- 驱动类 -->
<property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
<!-- url地址 -->
<property name="connection.url">jdbc:oracle:thin:@localhost:1521:orcl</property>
<property name="connection.username">system</property>
<property name="connection.password">1</property>
<!-- SQL dialect (SQL 方言) -->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<!-- Echo all executed SQL to stdout 在控制台打印后台的SQL语句 -->
<property name="show_sql">true</property>
<!-- 格式化显示SQL -->
<property name="format_sql">true</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<!-- 支持getCurrentSession方法 -->
<!-- <property name="current_session_context_class">thread</property> -->
<!-- 关联小配置 -->
<mapping resource="cn/entity/EmpInfo.hbm.xml" />
</session-factory>
</hibernate-configuration>
测试类：
public class Tests {
Session session;
Transaction tx;
@Before
public void initDate(){
session = HibernateUtil.getSession();
tx= session.beginTransaction();
}
@After
public void afterTest(){
tx.commit();
HibernateUtil.closeSession();
}
/**
* 组件的映射测试
*/
@Test
public void getTest(){
//创建一个员工对象
EmpInfo emp=new EmpInfo();
emp.setEname("火狐1");
//创建一个员工地址对象
EmpHomeAddress address=new EmpHomeAddress();
address.setEhomecity("北京");
address.setEhomeprovince("北京");
address.setEhomestreet("五道口");
address.setEhomezipcode("100000");
address.setEmpinfo(emp);
emp.setEhome(address);
session.save(emp);
System.out.println("ok");
}
/**
* 查询
*/
@Test
public void selectTest(){
EmpInfo emp=(EmpInfo)session.load(EmpInfo.class, 1);
System.out.println(emp.getEname());
}
}
结果：
数据库：
来源：https://www.cnblogs.com/jingpeipei/p/5842980.html