Hibernate中的一对一关联

2023-08-19 14:36:28

Hibernate提供了两种一对一映射关联关系的方式：

1）按照外键映射

2）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

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();

    }

}

创建实体类Users1和Resume1

Users1：

package cn.entity_fk;

/**

 * 员工类

 *

 *

 *

 */

public class Users1 {

    private Integer userid;//用户编号

    private String username;//名称

    private String userpass;//密码

    private Resume1 resume1;//档案对象

    public Users1() {

    }

    public Users1(String username, String userpass) {

        this.username = username;

        this.userpass = userpass;

    }

    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;

    }

}

Resume1:

package cn.entity_fk;

/**

 * 档案类

 *

 * @time

 * @author Happy

 *

 */

public class Resume1 {

    private Integer resid; //档案编号

    private String resname; //档案名称

    private String rescardno;//编号

    private Users1 users1;  //隶属的用户（员工）

    public Resume1() {

    }

    public Resume1( String resname, String rescardno) {

        this.resname = resname;

        this.rescardno = rescardno;

    }

    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;

    }

}

创建配置文件Users1.hbm.xml和Resume1.hbm.xml

Users1.hbm.xml:

<?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_fk">

   <class name="Users1" table="USERS1">

   <!-- 主键的配置 -->

     <id name="userid" column="USERID" >

        <!-- 由后台数据库生成主键：默认生成的序列名称为：Hibernate_Sequence -->

        <generator class="native"></generator>

     </id>

     <property name="username" column="USERNAME" type="string"></property>

     <property name="userpass" column="USERPASS" type="string"></property>

     <!-- 配置一对对，外键方式的关联

        property-ref:通过Resume1 的users1的属性，建立了从users1到Resume1的对象的关联！

      -->

     <one-to-one name="resume1" class="Resume1" property-ref="users1"></one-to-one>

   </class>

</hibernate-mapping>

Resume1.hbm.xml:

<?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_fk">

   <class name="Resume1" table="RESUME1">

     <id name="resid" column="RESID" >

        <generator class="native"></generator>

     </id>

     <property name="resname" column="RESNAME" type="string"></property>

     <property name="rescardno" column="RESCARDNO" type="string"></property>

     <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

     */

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();

     }

    /**

     * 一对一关联测试

     */

    @Test

    public void getTest(){

        Users1 u1=new Users1();

        u1.setUsername("火");

        u1.setUserpass("2");

        Resume1 r1=new Resume1();

        r1.setResname("培训2");

        r1.setRescardno("002");

        u1.setResume1(r1);

        r1.setUsers1(u1);

        session.save(r1);

        System.out.println("ok-------");

    }

    /**

     * 查询

     */

    @Test

    public void selectTest(){

         Users1 u1=(Users1)session.load(Users1.class, 2);

          System.out.println(u1.getResume1().getResname());

    }

结果：

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）

Resume2:

package cn.entity_pk;

/**

 * 档案类

 *

 * @time

 * @author Happy

 *

 */

public class Resume2 {

    private Integer resid;

    private String resname;

    private String rescardno;

    private Users2 users2;

    public Users2 getUsers2() {

        return users2;

    }

    public void setUsers2(Users2 users2) {

        this.users2 = users2;

    }

    public Resume2() {

    }

    public Resume2( String resname, String rescardno) {

        this.resname = resname;

        this.rescardno = rescardno;

    }

    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;

    }

}

Users2：

package cn.entity_pk;

/**

 * 员工类

 *

 * @author Happy

 *

 */

public class Users2 {

    private Integer userid;

    private String username;

    private String userpass;

    private Resume2 resume2;

    public Resume2 getResume2() {

        return resume2;

    }

    public void setResume2(Resume2 resume2) {

        this.resume2 = resume2;

    }

    public Users2() {

    }

    public Users2(String username, String userpass) {

        this.username = username;

        this.userpass = userpass;

    }

    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;

    }

}

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.entity_pk">

 <class name="Resume2" table="RESUME2">

  <id column="RESID" name="resid">

     <generator class="sequence">

       <param name="sequence">SEQ_NUM</param>

     </generator>

  </id>

  <property column="RESNAME" name="resname" type="string"/>

  <property column="RESCARDNO" name="rescardno" type="string"/>

  <!--主的一方  -->

  <one-to-one  name="users2" cascade="all" class="Users2" />

 </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.entity_pk">

   <class name="Users2" table="USERS2">

     <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>

     <!-- constrained:用来约束 在底层USERS2数据表中，植入外键-->

     <one-to-one name="resume2" class="Resume2" constrained="true"></one-to-one>

   </class>

</hibernate-mapping>

测试类：

public class Test_pk {

    Session session;

    Transaction tx;

    @Before

    public void initDate(){

        session = HibernateUtil.getSession();

         tx= session.beginTransaction();

    }

    @After

     public void afterTest(){

         tx.commit();

         HibernateUtil.closeSession();

     }

    /**

     * 一对一关联测试:按照主键映射

     */

    @Test

    public void getTest(){

        Users2 u1=new Users2();

        u1.setUsername("呵呵");

        u1.setUserpass("1");

        Resume2 r1=new Resume2();

        r1.setResname("哈哈");

        r1.setRescardno("001");

        u1.setResume2(r1);

        r1.setUsers2(u1);

        session.save(r1);

        System.out.println("ok-------");

    }

    /**

     * 查询

     */

    @Test

    public void selectTest(){

        Users2 u1=(Users2)session.load(Users2.class, 2);

        System.out.println(u1.getResume2().getResname());

    }

结果：

数据库：

Resume2表：

Users2表：

码农公寓

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