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Hibernate组件映射
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:
Hibernate组件映射
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