对于ORM而言，一个重要的特性就是对实体之间关联关系的管理。数据关联是ORM一个重要的特征，但往往也是导致性能低下的原因，在开发中要特别注意这一点。
一对一关联有两种类型：主键关联和唯一外键关联
一.主键关联：
一对一主键关联形式，即两张关联表通过主键形成一对一映射关系。
例如，一个中国公民只能有一份护照。
1.数据模型如下
2.表定义sql
DROP TABLE T_User;
DROP TABLE T_Passport;
CREATE TABLE T_Passport (
id INT NOT NULL
, serial VARCHAR ( 30 )
, expiry INT
, PRIMARY KEY (id)
);
CREATE TABLE T_User (
id INT NOT NULL AUTO_INCREMENT
, name VARCHAR ( 50 )
, age INT
, PRIMARY KEY (id)
, INDEX (id)
, CONSTRAINT FK_T_User_1 FOREIGN KEY (id)
REFERENCES T_Passport (id)
);
3.POJO类
TUser.java
package cn.blogjava.start;
public class TUser implements java.io.Serializable {
// Fields
private Integer id;
private Integer age;
private String name;
private TPassport passport;
// Constructors
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this .age = age;
}
public TPassport getPassport() {
return passport;
}
public void setPassport(TPassport passport) {
this .passport = passport;
}
/** default constructor */
public TUser() {
}
/** constructor with id */
public TUser(Integer id) {
this .id = id;
}
// Property accessors
public Integer getId() {
return this .id;
}
public void setId(Integer id) {
this .id = id;
}
public String getName() {
return this .name;
}
public void setName(String name) {
this .name = name;
}
}
TPassport.java
package cn.blogjava.start;
import java.io.Serializable;
public class TPassport implements Serializable {
private Integer id;
private String serial;
private Integer expiry;
private TUser user;
public Integer getExpiry() {
return expiry;
}
public void setExpiry(Integer expiry) {
this .expiry = expiry;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this .id = id;
}
public String getSerial() {
return serial;
}
public void setSerial(String serial) {
this .serial = serial;
}
public TUser getUser() {
return user;
}
public void setUser(TUser user) {
this .user = user;
}
}
3.配置文件
TUser.hbm.xml
<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="cn.blogjava.start.TUser" table ="T_User" catalog ="sample" >
< id name ="id" type ="integer" >
< column name ="id" />
< generator class ="native" />
</ id >
< property name ="name" type ="string" >
< column name ="name" length ="100" not-null ="true" />
</ property >
< property name ="age" type ="java.lang.Integer" column ="age" />
< one-to-one name ="passport"
class ="cn.blogjava.start.TPassport"
cascade ="all"
outer-join ="true"
/>
</ class >
</ hibernate-mapping >
TPassport.hbm.xml
<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="cn.blogjava.start.TPassport" table ="T_Passport" catalog ="sample" >
< id name ="id" type ="integer" column ="id" >
< generator class ="foreign" >
< param name ="property" > user </ param >
</ generator >
</ id >
< property name ="serial" type ="string" column ="serial" />
< property name ="expiry" type ="java.lang.Integer" column ="expiry" />
< one-to-one name ="user"
class ="cn.blogjava.start.TUser"
constrained ="true"
/>
</ class >
</ hibernate-mapping >
4.测试代码
package cn.blogjava.start;
import java.util.List;
import junit.framework.Assert;
import junit.framework.TestCase;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
public class HibernateTest extends TestCase {
Session session = null ;
protected void setUp() {
try {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
session = sessionFactory.openSession();
} catch (HibernateException e) {
e.printStackTrace();
}
}
protected void tearDown() {
try {
session.close();
} catch (HibernateException e) {
e.printStackTrace();
}
}
public void testInsert() {
Transaction tran = null ;
try {
TUser user = new TUser();
user.setName( " byf " );
user.setAge( new Integer( 26 ));
TPassport passport = new TPassport();
passport.setSerial( " PCN123456 " );
passport.setExpiry( new Integer( 20081010 ));
// 设置相互关联
user.setPassport(passport);
passport.setUser(user);
tran = session.beginTransaction();
session.save(user);
session.flush();
tran.commit();
Assert.assertEquals(user.getId().intValue() > 0 , true );
} catch (HibernateException e) {
e.printStackTrace();
Assert.fail(e.getMessage());
if (tran != null ) {
try {
tran.rollback();
} catch (Exception e1) {
e1.printStackTrace();
}
}
}
}
/**
* 对象读取测试(Select方法)
*/
public void testSelect(){
String hql = " from TUser where name='byf' " ;
try {
List userList = session.createQuery(hql).list();
TUser user = (TUser)userList.get( 0 );
System.out.println( " user name is " + user.getName());
System.out.println( " passport serial NO. is " + user.getPassport().getSerial());
Assert.assertEquals(user.getName(), " byf " );
} catch (Exception e) {
e.printStackTrace();
Assert.fail(e.getMessage());
}
}
}