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：
<!--因为现在员工对帐号是采用外键关联，所以在这里得加一个属性property-ref="employee"指定对方many-to-one 的name属性值-->
<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><!--在这边不再配置one-to-one了，而是用many-to-one，并且在many-to-one中加了unique="true"属性，表示唯一的多对一，也就成了一对一了，这里还得注意必须得指定外键column="empid" -->