Hibernate中的一对一关联和组件的映射

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：