一对一关联映射(采用唯一外键+单向)
一对一关联映射(采用唯一外键+单向)
hibernate一对一唯一外键关联映射(单向关联Person---->IdCard)
一对唯一外键关联映射是多对一关联映射的特例
可以采用<many-to-one>标签,指定多的一端的unique=true,这样就限制了多的一端的多重性为一
通过这种手段映射一对一唯一外键关联
第一步:首先建立实体关系类:如下:
person类的实体关系:
public class Person {
private int id;
private String name;
private IdCard idCard; //在Person类中持有IdCard的引用
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public IdCard getIdCard() {
return idCard;
}
public void setIdCard(IdCard idCard) {
this.idCard = idCard;
}
}
IdCord类的实体关系类如下:
public class IdCard {
private int id;
private String cardNo;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCardNo() {
return cardNo;
}
public void setCardNo(String cardNo) {
this.cardNo = cardNo;
}
}
第二步:加入实体类的关系映射:
IdCard类的实体映射文件如下:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
<id name="id">
<generator class="native"/>
</id>
<property name="cardNo"/>
</class>
</hibernate-mapping>
Person类的实体映射文件如下:
<hibernate-mapping>
<class name="com.bjsxt.hibernate.Person" table="t_person">
<id name="id">
<generator class="native"/>//这里的策略为自增。
</id>
<property name="name"/>
<many-to-one name="idCard" unique="true"/>//在这个属性里要加入unique属性,因为为一对一关系映射。这样就限制了他的唯一性
</class>
</hibernate-mapping>
第三步:加入Hibernate的配置文件:
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_one2one_ufk_1</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">bjsxt</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.show_sql">true</property>
<mapping resource="com/bjsxt/hibernate/IdCard.hbm.xml"/>
<mapping resource="com/bjsxt/hibernate/Person.hbm.xml"/>
</session-factory>
</hibernate-configuration>
第四步:写测试代码:
public class One2OneTest extends TestCase {
public void testSave1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setCardNo("88888888888888");
Person person = new Person();
person.setName("菜10");
person.setIdCard(idCard);
//不能成功保存,因为IdCard是Transient状态,必须先保存IdCard或者设置为cascade
session.save(person);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testSave2() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setCardNo("88888888888888");
session.save(idCard);//保存了之后就没问题了
Person person = new Person();
person.setName("菜10");
person.setIdCard(idCard);
session.save(person);
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
public void testLoad1() {
Session session = null;
try {
session = HibernateUtils.getSession();
session.beginTransaction();
Person person = (Person)session.load(Person.class, 2);
System.out.println("person.name=" + person.getName());
System.out.println("idCard.cardNo=" + person.getIdCard().getCardNo());
session.getTransaction().commit();
}catch(Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
}finally {
HibernateUtils.closeSession(session);
}
}
}