Hibernate（八）：基于外键映射的1-1关联关系

• 背景：

一个部门只有一个一把手，这在程序开发中就会设计数据映射应该设置为一对一关联。

在hibernate代码开发中，实现这个业务有两种方案：

1）基于外键映射的1-1关联；

2）基于主键映射的1-1关联。

本篇文章主要是用来学习如何使用外键实现1-1关联关系。

• 新建项目hibernate05

新建java project,引入依赖包，在src下添加hibernate.cfg.xml

 <?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>
         <property name="hibernate.connection.username">root</property>
         <property name="hibernate.connection.password">123456</property>
         <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
         <property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_01</property>

         <!-- <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
             <property name="hibernate.dialect">org.hibernate.dialect.MySQLInnoDBDialect</property> -->
         <property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>

         <property name="hibernate.show_sql">true</property>

         <property name="hibernate.format_sql">true</property>

         <property name="hibernate.hbm2ddl.auto">update</property>

         <property name="hibernate.current_session_context_class">thread</property>

         <property name="hibernate.c3p0.max_size">500</property>
         <property name="hibernate.c3p0.min_size">20</property>
         <property name="hibernate.c3p0.max_statements">10</property>
         <property name="hibernate.c3p0.timeout">2000</property>
         <property name="hibernate.c3p0.idle_test_period">2000</property>
         <property name="hibernate.c3p0.acquire_increment">10</property>

         <mapping resource="com/dx/hibernate005/onetoonebyforigenkey/Deparment.hbm.xml" />
         <mapping class="com.dx.hibernate005.onetoonebyforigenkey.Deparment" />
         <mapping resource="com/dx/hibernate005/onetoonebyforigenkey/Manager.hbm.xml" />
         <mapping class="com.dx.hibernate005.onetoonebyforigenkey.Manager" />
     </session-factory>
 </hibernate-configuration>

在src下新建包com.dx.hibernate005.onetoonebyforigenkey

在com.dx.hibernate005.onetoonebyforigenkey包下创建

Deparment.java

 package com.dx.hibernate005.onetoonebyforigenkey;

 public class Deparment {
     private Integer departId;
     private String departName;
     private Manager manager;

     public Deparment() {
         super();
     }

     public Deparment(Integer departId, String departName) {
         super();
         this.departId = departId;
         this.departName = departName;
     }

     public Integer getDepartId() {
         return departId;
     }

     public void setDepartId(Integer departId) {
         this.departId = departId;
     }

     public String getDepartName() {
         return departName;
     }

     public void setDepartName(String departName) {
         this.departName = departName;
     }

     public Manager getManager() {
         return manager;
     }

     public void setManager(Manager manager) {
         this.manager = manager;
     }

 }

Deparment.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2017-6-2 10:54:26 by Hibernate Tools 3.5.0.Final -->
 <hibernate-mapping>
     <class name="com.dx.hibernate005.onetoonebyforigenkey.Deparment" table="DEPARMENTS">
         <id name="departId" type="java.lang.Integer">
             <column name="DEPART_ID" />
             <generator class="native" />
         </id>
         <property name="departName" type="java.lang.String">
             <column name="DEPART_NAME" />
         </property>

         <!-- 在Deparment中定义一个Many-to-one就可以实现在Deparments表中多一个外键列 -->
         <many-to-one name="manager" class="com.dx.hibernate005.onetoonebyforigenkey.Manager" column="MANAGER_ID" unique="true"></many-to-one>
     </class>
 </hibernate-mapping>

Manager.java

 package com.dx.hibernate005.onetoonebyforigenkey;

 public class Manager {
     private Integer managerId;
     private String managerName;
     private Deparment deparment;

     public Manager() {
         super();
     }

     public Manager(Integer managerId, String managerName) {
         super();
         this.managerId = managerId;
         this.managerName = managerName;
     }

     public Integer getManagerId() {
         return managerId;
     }

     public void setManagerId(Integer managerId) {
         this.managerId = managerId;
     }

     public String getManagerName() {
         return managerName;
     }

     public void setManagerName(String managerName) {
         this.managerName = managerName;
     }

     public Deparment getDeparment() {
         return deparment;
     }

     public void setDeparment(Deparment deparment) {
         this.deparment = deparment;
     }

 }

Deparment.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2017-6-2 10:54:26 by Hibernate Tools 3.5.0.Final -->
 <hibernate-mapping>
     <class name="com.dx.hibernate005.onetoonebyforigenkey.Manager" table="MANAGERS">
         <id name="managerId" type="java.lang.Integer">
             <column name="MANAGER_ID" />
             <generator class="native" />
         </id>
         <property name="managerName" type="java.lang.String">
             <column name="MANAGER_NAME" />
         </property>

         <!-- 在对应的数据表中已经有了外键，当前持久化类使用one-to-one进行映射 -->
         <one-to-one name="deparment" class="com.dx.hibernate005.onetoonebyforigenkey.Deparment" property-ref="manager"></one-to-one>
     </class>
 </hibernate-mapping>

TestMain.java测试类,并引入JUnit4所需的依赖包。

package com.dx.hibernate005.onetoonebyforigenkey;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.model.naming.ImplicitNamingStrategyComponentPathImpl;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class TestMain {
    private SessionFactory sessionFactory = null;
    private Session session = null;
    private Transaction transaction = null;

    @Before
    public void init() {
        StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder().configure().build();
        Metadata metadata = new MetadataSources(standardRegistry).getMetadataBuilder().applyImplicitNamingStrategy(ImplicitNamingStrategyComponentPathImpl.INSTANCE).build();

        sessionFactory = metadata.getSessionFactoryBuilder().build();
        session = sessionFactory.getCurrentSession();
        transaction = session.beginTransaction();
    }

    @After
    public void destory() {
        transaction.commit();
        session.close();
        sessionFactory.close();
    }
}

运行空测试类，初始化sql:

 Hibernate: 

     create table DEPARMENTS (
        DEPART_ID integer not null auto_increment,
         DEPART_NAME varchar(255),
         MANAGER_ID integer,
         primary key (DEPART_ID)
     ) engine=InnoDB
 Hibernate: 

     create table MANAGERS (
        MANAGER_ID integer not null auto_increment,
         MANAGER_NAME varchar(255),
         primary key (MANAGER_ID)
     ) engine=InnoDB
 Hibernate: 

     alter table DEPARMENTS
        drop index UK_j9bdvgylyeboig73ntlfcuyf6
 Hibernate: 

     alter table DEPARMENTS
        add constraint UK_j9bdvgylyeboig73ntlfcuyf6 unique (MANAGER_ID)
 Hibernate: 

     alter table DEPARMENTS
        add constraint FKnlmf88ii3maigw7hgc182cqi4
        foreign key (MANAGER_ID)
        references MANAGERS (MANAGER_ID)

• 测试：

1)测试insert:

     @Test
     public void testInsert(){
         Deparment deparment=new Deparment();
         deparment.setDepartName("Depart1");

         Manager manager=new Manager();
         manager.setManagerName("manager1");

         deparment.setManager(manager);
         manager.setDeparment(deparment);

         session.save(manager);
         session.save(deparment);
     }
     

测试通过，测试打印sql

 Hibernate:
     insert
     into
         MANAGERS
         (MANAGER_NAME)
     values
         (?)
 Hibernate:
     insert
     into
         DEPARMENTS
         (DEPART_NAME, MANAGER_ID)
     values
         (?, ?)

2)测试select

     @Test
     public void testSelect() {
         // 1.查询时，采用懒加载。
         Deparment deparment = (Deparment) session.get(Deparment.class, 1);
         System.out.println(deparment.getDepartName());

         // // 2.会出现懒加载异常问题
         // session.close();
         // Manager manager = deparment.getManager();
         // System.out.println(manager.getClass());
         // System.out.println(manager.getManagerName());
     }

3)测试Select Manager

     @Test
     public void testSelectManager() {
         // 1.查询时，没采用懒加载。
         Manager manager = session.get(Manager.class, 1);
         System.out.println(manager.getManagerName());

         // 2.不会出现懒加载异常问题
         session.close();
         System.out.println(manager.getDeparment().getDepartName());
     }

4)测试修改

     @Test
     public void testUpdate() {
         // // 1) session关闭时，修改执行
         // Manager manager = session.get(Manager.class, 1);
         // manager.setManagerName("Mgr11111");
         // // session.save(manager);
         //
         // Deparment deparment = session.get(Deparment.class, 1);
         // deparment.setDepartName("Depart111111");
         // // session.save(deparment);

         // // 2)通过manager 关联修改deparment
         // Manager manager = session.get(Manager.class, 1);
         // manager.setManagerName("Mgr222");
         // manager.getDeparment().setDepartName("DEPT22");

         // 3)通过department关联修改manager
         Deparment deparment = session.get(Deparment.class, 1);
         deparment.setDepartName("DPT333");
         deparment.getManager().setManagerName("Mgr333");
     }

5）测试删除

     @Test
     public void testDelete() {
         // 1）在department表中有记录与之关联时，删除失败
         // Manager manager = session.get(Manager.class, 1);
         // session.delete(manager);

         // 2)删除成功，只删除了deparment表中的记录，manger表中的记录并没有删除，之后再删除manager就不会出现错误。
         Deparment deparment = session.get(Deparment.class, 1);
         session.delete(deparment);
     }