Hiberante part 9：一对一关系映射

 

一个男人对应一个女人，一个女人只能属于一个男人

 

方式一：外键映射

Male类

public class Male implements Serializable {
	private Integer id;
	private String name;
	private Integer age;
	private Female female;
}

 Male.hbm.xml，在male表中引入外键列female_id

<?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>
	<class name="rock.lee.bean.Male" table="male" catalog="test">
		<id name="id" column="id" type="int">
			<generator class="native"></generator>
		</id>
		<property name="name" column="name" type="java.lang.String"></property>
		<property name="age" column="age" type="int"></property>
		<many-to-one name="female" class="rock.lee.bean.Female"  unique="true" column="female_id"></many-to-one>
	</class>
</hibernate-mapping>

 
对于基于外键的1-1关联，其外键可以存放在任意一边，在需要存放外键一端，增加 many-to-one 元素。为 many-to-one元素增加 unique=“true” 属性来表示为1-1关联，并用name属性来指定关联属性的属性名

 

Female类

public class Female implements Serializable {
	private Integer id;
	private String name;
	private Integer age;
	private Male male;
}

 Female.hbm.xml

<?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>
	<class name="rock.lee.bean.Female" table="female" catalog="test">
		<id name="id" column="id" type="int">
			<generator class="native"></generator>
		</id>
		<property name="name" column="name" type="java.lang.String"></property>
		<property name="age" column="age" type="int"></property>
		<one-to-one name="male" class="rock.lee.bean.Male"  property-ref="female"></one-to-one>
	</class>
</hibernate-mapping>

 另一端需要使用one-to-one元素，该元素使用 property-ref 属性指定使用被关联实体主键以外的字段作为关联字段，也就是指定female在male表中的外键

在hibernate.cfg.xml中配置加载hbm文件

	<mapping resource="rock/lee/bean/Male.hbm.xml" />
	<mapping resource="rock/lee/bean/Female.hbm.xml" />

 测试保存

	@Test
	public void testOntToOne01() {
		Session session = HibernateUtils.openSession();
		Transaction transaction = session.beginTransaction();
		
		Male male = new Male("小明", 20);
		Female female = new Female("孙艺珍", 33);
		male.setFemale(female);
		female.setMale(male);
		
		session.save(male);
		session.save(female);
		
		transaction.commit();
		session.close();
	}

 测试惟一性：

mysql> select * from female;
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  1 | 孙艺珍       |   33 |
+----+--------+------+
1 row in set (0.00 sec)

mysql> select * from male;
+----+------+------+-----------+
| id | name | age  | female_id |
+----+------+------+-----------+
|  1 | 小明    |   20 |         1 |
+----+------+------+-----------+
1 row in set (0.00 sec)

 小明和孙艺珍离婚了，娶了孙艺珍的闺蜜林允儿

	@Test
	public void testOntToOne02() {
		Session session = HibernateUtils.openSession();
		Transaction transaction = session.beginTransaction();
		
		Male male = (Male) session.get(Male.class, 1);//查询小明
		Female female = new Female("林允儿", 26);
		male.setFemale(female);
		session.save(male);
		session.save(female);
		
		transaction.commit();
		session.close();
	}

 小明再婚成功

mysql> select * from female;
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  1 | 孙艺珍       |   33 |
|  2 | 林允儿      |   26 |
+----+--------+------+
2 rows in set (0.00 sec)

mysql> select * from male;
+----+------+------+-----------+
| id | name | age  | female_id |
+----+------+------+-----------+
|  1 | 小明    |   20 |         2 |
+----+------+------+-----------+
1 row in set (0.00 sec)

 几年后，林允儿看上了宋祖德，林允儿即不想离婚，又想和宋祖德在一起

	@Test
	public void testOntToOne03() {
		Session session = HibernateUtils.openSession();
		Transaction transaction = session.beginTransaction();
		
		Female female = (Female) session.get(Female.class, 2);
		Male male = new Male("宋祖德",55);
		male.setFemale(female);
		session.save(male);
		session.save(female);
		
		transaction.commit();
		session.close();
	}

 会抛出异常

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '1' for key 'female_id'

 可以对感情不忠，但不能重婚

 

逗逼一下：

 

	@Test
	public void testOntToOne04() {
		Session session = HibernateUtils.openSession();
		Transaction transaction = session.beginTransaction();
		
		Female female = (Female) session.get(Female.class, 1);
		Male male = new Male("博主",27);
		male.setFemale(female);
		session.save(male);
		session.save(female);
		
		transaction.commit();
		session.close();
	}

 

You To Me & Me To You Ⅰ

mysql> select * from female;
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  1 | 孙艺珍       |   33 |
|  2 | 林允儿      |   26 |
+----+--------+------+
2 rows in set (0.00 sec)

mysql> select * from male;
+----+------+------+-----------+
| id | name | age  | female_id |
+----+------+------+-----------+
|  4 | 博主     |   27 |         1 |
+----+------+------+-----------+
1 row in set (0.00 sec)

 

 

 

永远的初恋情人

 

方案二：主键映射

female表的主键是引用male的主键

Male.hbm.xml

	<hibernate-mapping>
		<class name="rock.lee.bean.male" table="male">
			<id name="id">
				<generator class="native"></generator>
			</id>
			<property name="name"></property>
			<one-to-one name="female" class="rock.lee.bean.Female"></one-to-one>
		</class>
	</hibernate-mapping> 

 Female.hbm.xml

	<hibernate-mapping>
		<class name="rock.lee.bean.Female" table="female">
			<id name="id">
				<generator class="foreign">
					<param name="property">company</param>
				</generator>
			</id>
			<property name="info"></property>
			<one-to-one name="male" class="rock.lee.bean.Male" constrained="true"></one-to-one>
		</class>
	</hibernate-mapping> 

 基于主键的映射策略:指一端的主键生成器使用 foreign 策略,表明根据”对方”的主键来生成自己的主键，自己并不能独立生成主键. <param> 子元素指定使用当前持久化类的那个属性作为 “对方”
采用foreign主键生成器策略的一端增加 one-to-one 元素映射关联属性，其 one-to-one 属性还应增加 constrained=“true” 属性；另一端(company)增加one-to-one元素映射关联属性。

constrained(约束):指定为当前持久化类对应的数据库表的主键添加一个外键约束，引用被关联的对象(“对方”)所对应的数据库表主键