Hibernate 关系映射(二)基于中间表的N:1

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Hibernate

n 对1 有中间表 join table many-to-one cascade="all"

1.单向 N:1 有中间表
例如:一个地方有多个人住.
     每个同学记住老师,比老师记住每个同学简单.
(在 n 的一端进行配置效率高)

N            1
Person   : Address
Student : Teacher

注意:这次是有中间表
注意:比较有无中间表的配置,发现采用 Join 和 many-to-one 进行配置
中间表

Person

Address

public class Address {
	private Integer aid;
	private String addressDetail;

        //set get ...
}

public class Person {

	private Integer pid;
	private String name;
	private int age;
	
	private Address address;  //单向(N:1)  反过来(1:1) 
	//set  get...
}

# person address N:1µÄ ÖÐ¼ä±í 
CREATE TABLE mytest.person_address
	(
	persson_id INT NOT NULL,
	address_id INT,
	PRIMARY KEY (persson_id),
	KEY FK23F8B90A67DFD9E4 (address_id),
	KEY FK23F8B90A5A57D6C9 (persson_id),
	CONSTRAINT FK23F8B90A5A57D6C9 FOREIGN KEY (persson_id) REFERENCES person (PID),
	CONSTRAINT FK23F8B90A67DFD9E4 FOREIGN KEY (address_id) REFERENCES address (AID)
	);

#Address
DROP TABLE IF EXISTS mytest.address;

CREATE TABLE mytest.address
	(
	AID         INT NOT NULL,
	ADDRESSDESC VARCHAR (255),
	PRIMARY KEY (AID)
	);
#Person	
DROP TABLE IF EXISTS mytest.person;

CREATE TABLE mytest.person
	(
	PID  INT NOT NULL,
	NAME VARCHAR (255),
	AGE  INT,
	PRIMARY KEY (PID)
	);

   <!--person-->
  <hibernate-mapping package="com.sh.study.model">
	<class name="Person" table="PERSON">
		<id name="pid" type="java.lang.Integer" column="PID">
			<generator class="increment"/>
		</id> 
		<property name="name" type="java.lang.String">
			<column name="NAME" />
		</property>
		<property name="age" type="int">
			<column name="AGE" />
		</property>
		
		<!-- Person 和 address 没有中间表的  N:1 配置  -->
		<!--name就是 Person中 的那个 address  
			cascade="all" 
		
		<many-to-one name="address" 
			class="Address" column="address_id">
		</many-to-one>
		-->
		
		<!-- person 和 address 有中间表的  N:1 配置   -->
		<join table="person_address">
			<key column="persson_id"/>
			<many-to-one name="address" cascade="all" class="Address" column="address_id"/>
		</join>
	</class>
</hibernate-mapping>


   <!--address-->
  <hibernate-mapping package="com.sh.study.model">
	<class name="Address" table="ADDRESS">
		<id name="aid" type="java.lang.Integer" column="AID">
			<generator class="increment"/>
		</id> 
		<property name="addressdesc" type="java.lang.String">
			<column name="ADDRESSDESC" />
		</property>
	</class>
</hibernate-mapping>

//test


public class TestHibernate {
	private ApplicationContext act;
	private SessionFactory factory;
	@Before
	public void init(){
		act = new ClassPathXmlApplicationContext("classpath:spring/applicationContext.xml");
		factory= act.getBean("sessionFactory",SessionFactory.class);
	}
	//测试 无  五间表的 N:1 关系
	@Test
	public void test1() {
		Session session=factory.getCurrentSession();
		Transaction tx=session.beginTransaction();
		Person p=new Person();
		p.setAge(12);
		p.setName("Yeeku");
		Address address=new Address();
		address.setAddressdesc("北京海淀区");
		p.setAddress(address);

		//持久化对象
		session.persist(p);
		session.flush();
		tx.commit();
	
		//如果不是使用的SessionFactory.getSession()来获得Session。
		//而是使用SessionFactory.getCurrentSession()方法来获得Session时，
		//当事务结束的时候，不管是提交还是回滚事务，hibernate会自动关闭Session的，
		//session.close();
	}
	
	//测试 无  中间表的 N:1 关系
	@Test
	public void test2() {
		Session session=factory.getCurrentSession();
		Transaction tx=session.beginTransaction();
		Person p=new Person();
		p.setAge(12);
		p.setName("Yeeku");
		Address address=new Address();
		address.setAddressdesc("北京海淀区");
		p.setAddress(address);

		//持久化对象
		session.persist(p);
		//修改 Person的 地址 
		Address address1=new Address();
		address1.setAddressdesc("上海虹口");
		p.setAddress(address1);
		tx.commit();
	}
}

注意:cascade="all"

<!--如果Person配置-->
<hibernate-mapping package="com.sh.study.model">
	<class name="Person" table="PERSON">
		<id name="pid" type="java.lang.Integer" column="PID">
			<generator class="increment"/>
		</id> 
		<property name="name" type="java.lang.String">
			<column name="NAME" />
		</property>
		<property name="age" type="int">
			<column name="AGE" />
		</property>
		<!--如果少了 下面这个  
			cascade="all" 
		-->
		<many-to-one name="address" 
			class="Address" column="address_id">
		</many-to-one>
	</class>
</hibernate-mapping>

会出现异常:

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.sh.study.model.Address