Hibernate组件映射

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。
EmpInfo实体类：
EmpHomeAddress实体类：

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;    }}

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.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:

<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());    }}