Hibernate提供了两种映射一对一映射关联关系的方式:
01.按照外键映射
02.按照主键映射
下面以员工账号表和员工档案表（员工账号和档案表之间是一对一的关系）为例，介绍这两种映射关系,并使用这两种 映射方式分别完成以下持久化操作
(1)保存员工档案的同时分配给员工一个账号
(2)加载员工档案的同时加载账号信息
一:按照外键映射
需要提示：
HibernateUtil工具类（用于获取session和关闭session）
package cn.zhang.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();
} }
Resume1.java实体类
package cn.zhang.entity;
public class Resume1 {
private Integer resid;
private String resname;
private String rescardno;
private Users1 users1;
public Resume1(String resname, String rescardno) {
super();
this.resname = resname;
this.rescardno = rescardno;
}
public Resume1() {
}
public Integer getResid() {
return resid;
}
public void setResid(Integer resid) {
this.resid = resid;
}
public String getResname() {
return resname;
}
public void setResname(String resname) {
this.resname = resname;
}
public String getRescardno() {
return rescardno;
}
public void setRescardno(String rescardno) {
this.rescardno = rescardno;
}
public Users1 getUsers1() {
return users1;
}
public void setUsers1(Users1 users1) {
this.users1 = users1;
}
}
Users1.java实体类
package cn.zhang.entity;
public class Users1 {
private Integer userid;
private String username;
private String userpass;
private Resume1 resume1;
public Users1(String username, String userpass) {
super();
this.username = username;
this.userpass = userpass;
}
public Users1() {
}
public Integer getUserid() {
return userid;
}
public void setUserid(Integer userid) {
this.userid = userid;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getUserpass() {
return userpass;
}
public void setUserpass(String userpass) {
this.userpass = userpass;
}
public Resume1 getResume1() {
return resume1;
}
public void setResume1(Resume1 resume1) {
this.resume1 = resume1;
}
}
Users1.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.zhang.entity">
<class name="Users1" table="USERS1">
<id name="userid" column="USERID" >
<generator class="sequence">
<param name="sequence">SQ_Num</param>
</generator>
</id>
<property name="username" column="USERNAME" type="string"></property>
<property name="userpass" column="USERPASS" type="string"></property>
<!-- 一对一关联 -->
<!-- property-ref属性为users1，表明通过Resume1的users1的属性建立从 Users1对象到Resume1对象的关联，如果不指定，它会默认两张表的主键联系，引发错误-->
<one-to-one name="resume1" class="Resume1" property-ref="users1"></one-to-one>
</class>
</hibernate-mapping>
Resume1.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.zhang.entity">
<class name="Resume1" table="RESUME1">
<id name="resid" column="RESID" >
<generator class="sequence">
<param name="sequence">SQ_Num</param>
</generator>
</id>
<property name="resname" column="RESNAME" type="string"></property>
<property name="rescardno" column="RESCARDNO" type="string"></property>
<!-- 一对一配置 -->
<!--column="RESUSERID": Resume1对应Users1表的外键关系 -->
<!--unique="true":表明每个Resume1对象都有唯一的Users1对象，确保唯一性-->
<!--cascade="all":级联 -->
<many-to-one name="users1" class="Users1" cascade="all" column="RESUSERID" unique="true"></many-to-one>
</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 -->
<property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@localhost:1521:orcl</property>
<property name="connection.username">***</property>
<property name="connection.password">***</property> <!-- SQL dialect (SQL 方言)-->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property> <!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">create</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> <!-- JDBC connection pool (use the built-in) -->
<!-- <property name="connection.pool_size">1</property> --> <!-- Enable Hibernate's automatic session context management 指定当前session范围和上下文-->
<!-- <property name="current_session_context_class">thread</property> --> <!-- Disable the second-level cache -->
<!-- <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>--> <mapping resource="cn/zhang/entity/Resume1.hbm.xml" />
<mapping resource="cn/zhang/entity/Users1.hbm.xml" /> </session-factory> </hibernate-configuration>
测试类:
/**
* 一对一关联测试
*/
@Test
public void testOne(){
Session session = HibernateUtil.currentSession();
Transaction tx=session.beginTransaction();
//创建一个用户对象
Users1 u1=new Users1("ZhangZong","521");
//创建一个档案对象
Resume1 r1=new Resume1("精英档案","好");
u1.setResume1(r1);
r1.setUsers1(u1);
//保存r1自动保存u1
session.save(r1);//以为Resume1设置了级联，保存r1，u1也会保存
tx.commit();
HibernateUtil.closeSession();
System.out.println("成功");
}
结果展示:
01.控制台
02.数据库
users1表
resume1表
二：按照主键映射
Users2表的userid字段是主键，同时作为外键参照Resume2表的主键，即Users2表与Resume2表共享主键（Users2中的主键值是根据Resume2生成的主键值取值的）
需要提示：
Resume2实体类:
package cn.zhang.entity;
public class Resume2 {
private Integer resid;
private String resname;
private String rescardno;
private Users2 users2;
public Resume2(String resname, String rescardno) {
super();
this.resname = resname;
this.rescardno = rescardno;
}
public Resume2() {
}
public Integer getResid() {
return resid;
}
public void setResid(Integer resid) {
this.resid = resid;
}
public String getResname() {
return resname;
}
public void setResname(String resname) {
this.resname = resname;
}
public String getRescardno() {
return rescardno;
}
public void setRescardno(String rescardno) {
this.rescardno = rescardno;
}
public Users2 getUsers2() {
return users2;
}
public void setUsers2(Users2 users2) {
this.users2 = users2;
}
}
Users2.java实体类
package cn.zhang.entity;
public class Users2 {
private Integer userid;
private String username;
private String userpass;
private Resume2 resume2;
public Users2(String username, String userpass) {
super();
this.username = username;
this.userpass = userpass;
}
public Users2() {
}
public Integer getUserid() {
return userid;
}
public void setUserid(Integer userid) {
this.userid = userid;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getUserpass() {
return userpass;
}
public void setUserpass(String userpass) {
this.userpass = userpass;
}
public Resume2 getResume2() {
return resume2;
}
public void setResume2(Resume2 resume2) {
this.resume2 = resume2;
}
}
Resume2.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.zhang.entity">
<class name="Resume2" table="RESUME2">
<!-- 主键的生成策略，Users2表中的主键userid会根据此来取值 -->
<id name="resid" column="RESID" >
<generator class="sequence">
<param name="sequence">SQ_Num</param>
</generator>
</id>
<property name="resname" column="RESNAME" type="string"></property>
<property name="rescardno" column="RESCARDNO" type="string"></property>
<!-- 一对一配置 -->
<one-to-one name="users2" class="Users2" cascade="all"></one-to-one>
</class>
</hibernate-mapping>
Users2.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.zhang.entity">
<class name="Users2" table="USERS2">
<!-- foreign生成策略，根据Resume2的主键生成策略 -->
<id name="userid" column="USERID" >
<generator class="foreign">
<param name="property">resume2</param>
</generator>
</id>
<property name="username" column="USERNAME" type="string"></property>
<property name="userpass" column="USERPASS" type="string"></property>
<!-- 一对一关联 -->
<!--constrained="true":表明 Users2表的userid主键同时作为外键参照Resume2表的主键-->
<one-to-one name="resume2" class="Resume2" constrained="true"></one-to-one>
</class>
</hibernate-mapping>
测试：
/**
* 一对一关联测试:按照主键映射
*/
@Test
public void testOne(){
Session session = HibernateUtil.currentSession();
Transaction tx=session.beginTransaction();
//创建一个用户对象
Users2 u1=new Users2("ZhangZong","521");
//创建一个档案对象
Resume2 r1=new Resume2("精英档案","好");
u1.setResume2(r1);
r1.setUsers2(u1);
//保存r1自动保存u1
session.save(r1);
tx.commit();
HibernateUtil.closeSession();
System.out.println("成功");
}
结果展示:
01.控制台
02.数据库
Resume2表
Users2表
三：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
需要提示：
EmpHomeAddress.java实体类
package cn.zhang.entity;
//员工地址信息实体类
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.java实体类
package cn.zhang.entity;
//员工实体类
public class EmpInfo {
private Integer eid;
private String ename;
private EmpHomeAddress ehome;//地址信息
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.zhang.entity">
<class name="EmpInfo" table="EMPINFO">
<id name="eid" column="EID">
<generator class="native"></generator>
</id>
<property name="ename" column="ENAME" type="string"></property>
<!--组件的映射配置 -->
<!--component元素表明 ehome属性是EmpInfo类的一个组成部分
name设定被映射的持久化类的属性名
-->
<component name="ehome" class="EmpHomeAddress">
<!-- parent指定EmpHomeAddress类所属的整体类 -->
<parent name="empinfo"/>
<!-- 基本映射 -->
<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>
测试类:
/**
* 组件的映射测试
*/
@Test
public void testOne(){
Session session = HibernateUtil.currentSession();
Transaction tx=session.beginTransaction();
//创建一个员工对象
EmpInfo emp=new EmpInfo();
emp.setEname("张总"); //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);
tx.commit();
HibernateUtil.closeSession();
System.out.println("成功");
}
测试结果展示：
01.控制台
02.数据库
EMPINFO表：