Hibernate中的一对一关系详解(1)

A:先讲讲一对一的关系(欲知其他关系，请看下篇)

a:主键关联的一对一关系

一对一关系一般用主键关联，也就是说用主键值来维护两者的关系，一个表的主键存放另一个表的主键值。例如在员工与帐号中，我们取员工表的主键值作为帐号的主键值。

我们一员工表和账号表为例：(员工表是主表，账号表是从表)

对持久化的对象的封装和get，set方法已省略，值得注意的是：vo中必须相互写上对方的对象：如在employee中要定义private AccountVo account，在account中也要写上对应的employee，我们只对映射文件与测试编写

主表的mapping配置：使用了one-to-one

<?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="com.ysq.vo">

         <class name="EmployeeVo" table="employee">

       <id name="oid">

          <generator class="sequence">

            <param name="sequence">dept_seq</param>  <!-- 使用的Oracle数据库，主键增长方式是sequence-->

          </generator>

       </id>

       <property name="deptid">

         <column name="deptid"/>

       </property>

       <property name="empName">

         <column name="empName" length="20"/>

       </property>

       <property name="sex">

         <column name="sex" length="2"/>

       </property>

       <property name="birthday">

         <column name="birthday" length="30"/>

       </property>

       <property name="school">

         <column name="school" length="20"/>

       </property>

       <property name="major">

         <column name="major" length="10"/>

       </property>

       <property name="degree">

         <column name="degree"/>

       </property>

       <property name="phone">

         <column name="phone" length="12"/>

       </property>

<one-to-one name="account" class="AccountVo" cascade="all"></one-to-one>

     </class>

</hibernate-mapping>

从表的mapping配置：

 <?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="com.ysq.vo">

      <class name="AccountVo" table="account">

        <id name="oid" type="java.lang.Integer">

            <column name="oid" />

            <generator class="foreign" ><!-- 采用外键方式生成主键值 -->

                 <param name="property">employee</param><!-- 表示取员工的主键值作为帐号的主键值，这里的employee要跟下面的<one-to-one>的name属性值一致 -->

            </generator>

        </id>

        <property name="username" type="java.lang.String">

            <column name="username" length="20" />

        </property>

        <property name="password" type="java.lang.String">

            <column name="password" length="20" />

        </property>

        <property name="email" type="java.lang.String">

            <column name="email" length="100" />

        </property>

        <property name="inactive" type="java.lang.String">

            <column name="inactive" length="1" />

        </property>

        <one-to-one name="employee" class= "EmployeeVo" constrained="true"></one-to-one>

   </class>

</hibernate-mapping>

对应的测试类：

 //添加员工信息，同时也添加了对应的账号
@Test

    public void addEmployee(){

          EmployeeVo employee = new EmployeeVo();

          AccountVo account = new AccountVo();  

          account.setUsername("zhangsan21");

          account.setEmail("csw-java@163.com");

          account.setPassword("123");

          employee.setBirthday("2003-09-09");

          employee.setEmpName("lizi21");

          employee.setPhone("1232132");

          Session session = SessionFactoryUtils.getSession();

          Transaction tr = session.beginTransaction();

          try {

            tr.begin();

             /* //保存员工

              session.save(employee);

              //保存帐号

               account.setEmployee(employee);

               session.save(account);*/

             //也可以进行双向关联，对主表进行save()

               account.setEmployee(employee);

               employee.setAccount(account);

               session.save(employee);//保存员工时，级联保存了账号

              tr.commit();

        } catch (HibernateException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }finally{

            session.close();

        }

    }

@Test    //修改和删除

    public void updateEmp(){

        .......

          try {

            tr.begin();

             //设置了双向关联，当对员工修改时，对account也进行了修改

                employee.setAccount(account);

                account.setEmployee(employee);

               session.update(employee);

               tr.commit();

        } catch (HibernateException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }finally{

            session.close();

        }

    }

    @Test

    public void deleteEmp(){

         ........

          Session session = SessionFactoryUtils.getSession();

          Transaction tr = session.beginTransaction();

          try {

            tr.begin();

                //设置双向关联

                employee.setAccount(account);

                account.setEmployee(employee);

               session.delete(employee);

               tr.commit();

        } catch (HibernateException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }finally{

            session.close();

        }

    }

@Test   //查询信息

    public void findEmployeeById(){

        Session session = SessionFactoryUtils.getSession();

        //一对一默认的延迟加载    get(class clazz,id)只针对通过id查询

        EmployeeVo employee = (EmployeeVo)session.get(EmployeeVo.class, 6);

        session.close();

        System.out.println(employee);

        System.out.println(employee.getAccount().getUsername());//注意：我这里的打印是引用了vo中的toString()方法，但只能在一个封装类中写toString()方法，同时写两个会报错的

    }

    @SuppressWarnings("unchecked")

    @Test

    public void findEmployee(){

        Session session = SessionFactoryUtils.getSession();

        //一对一默认的延迟加载[HQL]

        List<EmployeeVo> emps = session.createQuery("from EmployeeVo").list();

        session.close();

        for (EmployeeVo employee2 : emps) {

             System.out.println(employee2);

             System.out.println(employee2.getAccount().getUsername());

             System.out.println();

        }

    }

b:使用外键关联一对一的关系

只需要包对应的mapping文件中修改一些就可以了

如：employee中的：<one-to-one name="account" class="AccountVo" cascade="all"></one-to-one>需要修改如下：

<one-to-one name="account" class="AccountVo" property-ref="employee" cascade="all"></one-to-one>

account中的：<one-to-one name="employee" class= "EmployeeVo" constrained="true"></one-to-one> 需要修改如下：

<many-to-one name="employee" class="EmployeeVo" column="empid" unique="true"></many-to-one>

巴特西

Hibernate中的一对一关系详解(1)

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