第一种一对一
person和card,card的id即作为主键,又作为外键
// 各村对方的一个对象
public class Person { private Integer id;
private String name;
private Card card;
}
public class Card { private Integer id;
private String cardnum;
private Person person;
}
xxx.hbm.xml 的配置
记得在总配置文件中添加这两个配置文件
<?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.kaishengit.pojo"> <class name="Card" table="card">
<id name="id">
<!-- 主键生成策略变成foreign,表示又当主键又当外键 -->
<generator class="foreign">
<!-- 这个person是属性,指明用card这个类的person属性对应的表的主键作外键 -->
<param name="property">person</param>
</generator>
</id>
<property name="cardnum"/>
<one-to-one name="person" class="Person"/>
</class> </hibernate-mapping>
<?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.kaishengit.pojo"> <class name="Person" table="person">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<!-- cascade="delete"表示删除人的时候把卡删了 -->
<one-to-one cascade="delete" name="card" class="Card"/> </class> </hibernate-mapping>
程序执行
Person p = new Person();
p.setUsername("tom"); Card c = new Card();
c.setCardnum("12");
c.setPerson(p); session.save(p);
session.save(c);
/* 这时候有两条sql,都是insert,改变save(p),save(c)的顺序式没用的
因为card的insert必须要有id,id不能为空,因为它作为主键,所以程序只能
先save(p)*/ Person p = new Person();
p.setUsername("tom"); Card c = new Card();
c.setCardnum("12"); p.setCard(c); session.save(p);
session.save(c); /* 这样做就会报错了,因为主键的生成策略是从card找person属性
所以这种情况就只能让又当主键又当外键的那个表来维护关系 */
查询 这种情况下的查询都是联接查询,有捆绑性
Card card = (Card) session.get(Card.class, 2);
System.out.println(card.getCardnum());
System.out.println(card.getPerson().getName()); Person p = (Person) session.get(Person.class, 2);
System.out.println(p.getName());
System.out.println(p.getCard().getCardnum());
删除
<?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.kaishengit.pojo"> <class name="Person" table="person">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<!-- cascade="delete"表示删除人的时候把卡删了 -->
<one-to-one cascade="delete" name="card" class="Card"/> </class> </hibernate-mapping>
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第二种一对一,是一对多或者多对一的特殊情况,具有延迟加载的能力
dept和Employee,dept中有eid,Employee中有deptid
// 各村对方的一个对象
public class Dept { private Integer id;
private String name;
private Employee employee;
}
public class Employee { private Integer id;
private String name;
private Dept dept;
}
xxx.hmb.xml的配置
<?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.kaishengit.pojo"> <class name="Dept" table="dept">
<id name="id">
<generator class="native"/>
</id> <property name="name"/>
<!-- 是多对一的特殊情况,需要指定unique="true"唯一性 -->
<many-to-one name="employee" class="Employee" unique="true" column="eid"/> </class> </hibernate-mapping>
<?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.kaishengit.pojo"> <class name="Employee" table="employee">
<id name="id">
<generator class="native"/>
</id> <property name="name"/>
<!-- 是多对一的特殊情况,需要指定unique="true"唯一性 -->
<many-to-one name="dept" class="Dept" unique="true" column="deptid"/> </class> </hibernate-mapping>
程序执行
Employee e = new Employee();
e.setName("jack"); Dept d = new Dept();
d.setName("hr"); d.setEmployee(e); e.setDept(d); session.save(e);
session.save(d);
请看这里,这是双向维护关系,而且必须双向维护关系,不可避免的会多一条update语句