一、概述
我们以Company与Address类为例，介绍映射一对一关联关系的方法。
一对一的关联方法有两种
-按照外键映射：两个表任意一个表定义一个外键，来关联另一个表。
-按照主键映射：一个表的主键同时作为外键，和另一个表的主键保持一致。
二、按照外键映射
（1）创建实体类
public class Company {
private Integer id;
private String name;
private Address address;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}
public class Address {
private Integer id;
private String name;
private Company company;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Company getCompany() {
return company;
}
public void setCompany(Company company) {
this.company = company;
}
}
（2）我们配置映射文件，我们在Company这一方设置外键来关联Address 有外键的一方要使用<many-to-one>元素来配置。
Company.hbm.xml
<hibernate-mapping >
<class name="com.cad.domain.Company" table="company">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"></property>
<!--column指定外键，unique指定外键唯一约束，设为true，就可以表达Company和Address对象之间的一对一关联-->
<many-to-one name="address" class="com.cad.domain.Address" column="aid" unique="true"></many-to-one>
</class>
</hibernate-mapping>
Address.hbm.xml
<hibernate-mapping >
<class name="com.cad.domain.Address" table="address">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"></property>
<!--property-ref属性指定通过从Company的address属性来查找自己-->
<one-to-one name="Company" class="com.cad.domain.Company" property-ref="address"></one-to-one>
</class>
</hibernate-mapping>
测试：
public class Demo {
private Session session;
@Test
public void test() {
//读取配置文件
Configuration conf=new Configuration().configure();
//根据配置创建factory
SessionFactory sessionfactory=conf.buildSessionFactory();
session = sessionfactory.openSession();
Transaction ts=session.beginTransaction();
Company c=new Company();
c.setName("百度");
Address a=new Address();
a.setName("深圳");
c.setAddress(a);
a.setCompany(c);
session.save(a);
session.save(c);
ts.commit();
session.close();
sessionfactory.close();
}
}
默认情况下，一对一关联采用迫切左外连接检索策略。
三、按照主键映射
实体类不变，我们编写一下配置文件
address的表的id字段既是主键又是外键.
编写配置文件
Company.hbm.xml
<hibernate-mapping >
<class name="com.cad.domain.Company" table="company">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"></property>
<one-to-one name="address" class="com.cad.domain.Address" ></one-to-one>
</class>
</hibernate-mapping>
Address.hbm.xml
<hibernate-mapping >
<class name="com.cad.domain.Address" table="address">
<id name="id" column="id">
<!--必须使用foreign标识符生成策略，还要指定哪个对象共享OID-->
<generator class="foreign">
<param name="property">company</param>
</generator>
</id>
<property name="name" column="name"></property>
<!--constrained属性设为true，说明主键同时作为外键-->
<one-to-one name="company" class="com.cad.domain.Company" constrained="true"></one-to-one>
</class>
</hibernate-mapping>