| 只要你肯努力，没有什么事情是你不能搞砸的。 |
需求：一个汽车（Car）有一个引擎（Engine），它是一对一的映射关系。
对于一对一的映射，有两种实现方式：基于外键的映射和基于主键的映射。这两种方式学习的重点就是映射文件的配置，推荐使用第一种方式。
1、基于外键的映射Car.java
package com.rk.hibernate.k_one2one;
public class Car
{
private int carId;
private String carName;
private Engine engine;
public int getCarId()
{
return carId;
}
public void setCarId(int carId)
{
this.carId = carId;
}
public String getCarName()
{
return carName;
}
public void setCarName(String carName)
{
this.carName = carName;
}
public Engine getEngine()
{
return engine;
}
public void setEngine(Engine engine)
{
this.engine = engine;
}
@Override
public String toString()
{
return "Car [carId=" + carId + ", carName=" + carName + "]";
}
}Car.hbm.xml，注意many-to-one的映射
<?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.rk.hibernate.k_one2one" auto-import="true"> <class name="Car" table="T_Car"> <id name="carId" column="id"> <generator class="native"></generator> </id> <property name="carName" column="name"></property> <!-- 一对一映射，有外键方 unique="true" 给外键字段添加唯一约束 --> <many-to-one name="engine" column="engineId" class="Engine" unique="true"></many-to-one> </class> </hibernate-mapping>
Engine.java
package com.rk.hibernate.k_one2one;
public class Engine
{
private int engineId;
private String engineName;
private Car car;
public int getEngineId()
{
return engineId;
}
public void setEngineId(int engineId)
{
this.engineId = engineId;
}
public String getEngineName()
{
return engineName;
}
public void setEngineName(String engineName)
{
this.engineName = engineName;
}
public Car getCar()
{
return car;
}
public void setCar(Car car)
{
this.car = car;
}
@Override
public String toString()
{
return "Engine [engineId=" + engineId + ", engineName=" + engineName + "]";
}
}Engine.hbm.xml，注意one-to-one映射
<?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.rk.hibernate.k_one2one" auto-import="true"> <class name="Engine" table="T_Engine"> <id name="engineId" column="id"> <generator class="native"></generator> </id> <property name="engineName" column="name" type="string" length="20"/> <!-- 一对一映射： 没有外键方 --> <one-to-one name="car" class="Car"></one-to-one> </class> </hibernate-mapping>
App.java
package com.rk.hibernate.k_one2one;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App
{
private static SessionFactory sf;
static
{
sf = new Configuration()
.configure()
.addClass(Car.class)
.addClass(Engine.class)
.buildSessionFactory();
}
@Test
public void testSave()
{
int i = 2;
Session session = sf.openSession();
session.beginTransaction();
//引擎
Engine engine = new Engine();
engine.setEngineName("Super Engine" + i);
//汽车
Car car = new Car();
car.setCarName("BMW" + i);
car.setEngine(engine); //汽车和引擎的关系
session.save(engine);
session.save(car);
session.getTransaction().commit();
session.close();
}
@Test
public void testGet()
{
Session session = sf.openSession();
session.beginTransaction();
// Car car = (Car)session.get(Car.class, 2);
// System.out.println(car);
// Engine engine = car.getEngine();
// System.out.println(engine);
Engine e2 = (Engine)session.get(Engine.class, 3);
System.out.println(e2);
Car c2 = e2.getCar();
System.out.println(c2);
session.getTransaction().commit();
session.close();
}
}Car.java
package com.rk.hibernate.l_one2one_primarykey;
public class Car
{
private int carId;
private String carName;
private Engine engine;
public int getCarId()
{
return carId;
}
public void setCarId(int carId)
{
this.carId = carId;
}
public String getCarName()
{
return carName;
}
public void setCarName(String carName)
{
this.carName = carName;
}
public Engine getEngine()
{
return engine;
}
public void setEngine(Engine engine)
{
this.engine = engine;
}
@Override
public String toString()
{
return "Car [carId=" + carId + ", carName=" + carName + "]";
}
}Car.hbm.xml，注意one-to-one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.rk.hibernate.l_one2one_primarykey" auto-import="true"> <class name="Car" table="T_Car2"> <id name="carId" column="id"> <generator class="native"></generator> </id> <property name="carName" column="name"></property> <!-- 一对一映射 --> <one-to-one name="engine" class="Engine"></one-to-one> </class> </hibernate-mapping>
Engine.java，注意当前类的carId属性是T_Engine2表的主键，也是T_Car2的外键。
package com.rk.hibernate.l_one2one_primarykey;
public class Engine
{
private int carId;
private String engineName;
private Car car;
public int getCarId()
{
return carId;
}
public void setCarId(int carId)
{
this.carId = carId;
}
public String getEngineName()
{
return engineName;
}
public void setEngineName(String engineName)
{
this.engineName = engineName;
}
public Car getCar()
{
return car;
}
public void setCar(Car car)
{
this.car = car;
}
@Override
public String toString()
{
return "Engine [carId=" + carId + ", engineName=" + engineName + "]";
}
}Engine.hbm.xml，注意id和one-to-one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.rk.hibernate.l_one2one_primarykey" auto-import="true"> <class name="Engine" table="T_Engine2"> <id name="carId" column="car_id"> <!-- id 节点指定的是主键映射, 即car_id是主键 主键生成方式： foreign 即把别的表的主键作为当前表的主键； property (关键字，不能修改)指定引用的对象 --> <generator class="foreign"> <param name="property">car</param> </generator> </id> <property name="engineName" column="name" type="string" length="20"/> <!-- 一对一映射，有外键方 （基于主键的映射） constrained="true" 指定在主键上添加外键约束 --> <one-to-one name="car" class="Car" constrained="true"></one-to-one> </class> </hibernate-mapping>
App.java
package com.rk.hibernate.l_one2one_primarykey;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App
{
private static SessionFactory sf;
static
{
sf = new Configuration()
.configure()
.addClass(Car.class)
.addClass(Engine.class)
.buildSessionFactory();
}
@Test
public void testSave()
{
int i = 0;
Session session = sf.openSession();
session.beginTransaction();
//汽车
Car car = new Car();
car.setCarName("BMW" + i);
//引擎
Engine engine = new Engine();
engine.setEngineName("Super Engine" + i);
engine.setCar(car);
session.save(car);
session.save(engine);
session.getTransaction().commit();
session.close();
}
@Test
public void testGet()
{
Session session = sf.openSession();
session.beginTransaction();
Car car = (Car)session.get(Car.class, 1);
System.out.println(car);
Engine engine = car.getEngine();
System.out.println(engine);
// Engine e2 = (Engine)session.get(Engine.class, 1);
// System.out.println(e2);
// Car c2 = e2.getCar();
// System.out.println(c2);
session.getTransaction().commit();
session.close();
}
}
