依然是学生和学生卡的关联，这次是一对一单项主键关联
student.cfg.xml:
<?xml version="1.0"?>
<!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.edu.hpu.model">
<class name="Student" table="student" dynamic-update="true">
<id name="id" column="id">
<!-- 靠外键的关联来设置主键 class="foreign" -->
<generator class="foreign">
<param name="property">student</param>
</generator>
</id>
<property name="name"></property>
<property name="age"></property>
</class>
</hibernate-mapping>
（只改了这里）
StuIDCard.cfg.xml:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="cn.edu.hpu.model.StuIDCard">
<id name="id">
<generator class="native"></generator>
</id>
<property name="num"/>
<one-to-one name="student"></one-to-one>
</class>
</hibernate-mapping>
生成的建表语句，StuIDCard里面也没有了student_id
create table StuIDCard (
id integer not null auto_increment,
num varchar(255),
primary key (id)
)
create table student (
id integer not null,
name varchar(255) not null,
age integer,
primary key (id, name)
)
schema export complete
但是你会发现没有建立外键联系，这个时候就很危险，会产生id不一致的情况！
如何在xml配置文件中进行外键联系：
<one-to-one name="student" constrained="true"></one-to-one>
constrained="true"意思就是帮你加一个外键关联约束。
新的建表语句：
create table StuIDCard (
id integer not null auto_increment,
num varchar(255),
primary key (id)
)
create table student (
id integer not null,
name varchar(255),
age integer,
primary key (id)
)
alter table StuIDCard
add index FKD1E159DFFB389035 (id),
add constraint FKD1E159DFFB389035
foreign key (id)
references student (id)
schema export complete
可以看到，已经加了外键关联(StuIDCard的ID字段上有小钥匙的图标)
