hibernate基于外键的一对一映射--单向和双向

我就是我 2022-06-12 05:50 267阅读 0赞

hibernate基于外键的一对一映射和单向的多对一映射，很相似，不同的地方就是，在单向多对一映射中的实体类多的一端配置unique=“true”，就变为了外键的一对一映射。

基于外键的一对一映射可以分为两种情况：

一种是：单向；

一种是：双向；

# 下面先说单向 #

具体如下：

新建一个java项目，名称为：13hibernate\_single\_one\_to\_one\_foreign

项目结构如图：

![Center][]

需要的jar包以及如何从hibernate官网获得，可以参见《[Hibernate环境搭建和配置][Hibernate]》

实体类IdCard代码：

package com.robert.pojo;
    
    public class IdCard {
    
    	private int id ;
    	private String code ;//身份证号
    	public int getId() {
    		return id;
    	}
    	public void setId(int id) {
    		this.id = id;
    	}
    	public String getCode() {
    		return code;
    	}
    	public void setCode(String code) {
    		this.code = code;
    	}
    }

IdCard.hbm.xml配置文件代码：

实体类Person代码：

package com.robert.pojo;
    
    public class Person {
    
    	private int id ;
    	private String name ;//姓名
    	private int age ;//年龄
    	private IdCard idCard ;//身份证实体类
    	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 int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    	public IdCard getIdCard() {
    		return idCard;
    	}
    	public void setIdCard(IdCard idCard) {
    		this.idCard = idCard;
    	}
    	
    }

Person.hbm.xml配置文件代码：

<?xml version="1.0"?>
    <!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.robert.pojo">
    	<class name="Person">
    		<id name="id">
    			<generator class="native"></generator>
    		</id>
    		<property name="name"></property>
    		<property name="age"></property>
    		
    		<many-to-one name="idCard" class="IdCard" column="idcard_id"
    			foreign-key="fk_idcard" not-null="true" unique="true" cascade="save-update" />
    
    	</class>
    </hibernate-mapping>

HibernateUtil封装的操作session的代码，请参见《 [Hibernate联合主键][Hibernate 1]》中的HibernateUtil类代码

hibernate.cfg.xml代码：

<!DOCTYPE hibernate-configuration PUBLIC
    	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    
    <hibernate-configuration>
    <session-factory>
    	
    	<property name="connection.driver_class">
    		com.mysql.jdbc.Driver
    	</property>
    	<property name="connection.url">jdbc:mysql:///hibernate4</property>
    	<property name="connection.username">root</property>
    	<property name="connection.password">root</property>
    	
    	<property name="hibernate.dialect">
    		org.hibernate.dialect.MySQL5Dialect
    	</property>
    	
    	<property name="show_sql">true</property>
    	
    	<property name="format_sql">true</property>
    	
    	<property name="hbm2ddl.auto">update</property>
    
    	
    	<mapping resource="com/robert/pojo/IdCard.hbm.xml" />
    	<mapping resource="com/robert/pojo/Person.hbm.xml" />
    
    </session-factory>
    </hibernate-configuration>

测试类HibernateTest代码：

package com.robert.test;
    
    import java.io.IOException;
    import java.sql.SQLException;
    
    import javax.sql.rowset.serial.SerialException;
    
    import org.hibernate.HibernateException;
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.tool.hbm2ddl.SchemaExport;
    import org.junit.Test;
    
    import com.robert.pojo.IdCard;
    import com.robert.pojo.Person;
    import com.robert.util.HibernateUtil;
    
    public class HibernateTest {
    
    	/**
    	 * 根据*.hbm.xml文件对应的生成数据库表
    	 */
    	@Test
    	public void testCreateDB() {
    		Configuration cfg = new Configuration().configure();
    		SchemaExport se = new SchemaExport(cfg);
    		// 第一个参数：是否生成ddl脚本
    		// 第二个参数：是否执行到数据库中
    		se.create(true, true);
    	}
    
    	/**
    	 * 保存数据
    	 * 
    	 * @throws HibernateException
    	 * @throws SerialException
    	 * @throws SQLException
    	 * @throws IOException
    	 */
    	@Test
    	public void testSave() throws HibernateException, SerialException,
    			SQLException, IOException {
    		Session session = null;
    		Transaction tx = null;
    		try {
    			session = HibernateUtil.getSession();
    			tx = session.beginTransaction();
    
    			IdCard idCard = new IdCard() ;
    			idCard.setCode("1525271000000000000") ;
    			
    			Person person = new Person() ;
    			person.setAge(23) ;
    			person.setName("张三") ;
    			person.setIdCard(idCard) ;
    
    			session.save(person) ;
    			
    			IdCard idCard2 = new IdCard() ;
    			idCard2.setCode("11011010000000000") ;
    			
    			Person person2 = new Person() ;
    			person2.setAge(24) ;
    			person2.setName("李四") ;
    			person2.setIdCard(idCard2) ;
    			
    			session.save(person2);
    			
    
    			tx.commit();
    
    		} catch (HibernateException e) {
    			if (tx != null) {
    				tx.rollback();
    			}
    			e.printStackTrace();
    			throw e;
    		} finally {
    			HibernateUtil.closeSession();
    		}
    	}
    
    
    }

首先使用Junit4执行testCreateDB类，根据实体类重新生成数据库表

sql语句如下：

alter table Person 
            drop 
            foreign key fk_idcard
    
        drop table if exists IdCard
    
        drop table if exists Person
    
        create table IdCard (
            id integer not null auto_increment,
            code varchar(255),
            primary key (id)
        )
    
        create table Person (
            id integer not null auto_increment,
            name varchar(255),
            age integer,
            idcard_id integer not null,
            primary key (id)
        )
    
        alter table Person 
            add constraint UK_cbcosmln3841mbhco46ibil26 unique (idcard_id)
    
        alter table Person 
            add constraint fk_idcard 
            foreign key (idcard_id) 
            references IdCard (id)

执行testSave()方法，控制台console打印的sql语句如下：

Hibernate: 
        insert 
        into
            IdCard
            (code) 
        values
            (?)
    Hibernate: 
        insert 
        into
            Person
            (name, age, idcard_id) 
        values
            (?, ?, ?)
    Hibernate: 
        insert 
        into
            IdCard
            (code) 
        values
            (?)
    Hibernate: 
        insert 
        into
            Person
            (name, age, idcard_id) 
        values
            (?, ?, ?)

由打印的sql语句，可见保存数据时，当往person表中添加person的数据时，发现有关联的IdCard外键，所以要先添加它关联的IdCard数据，然后在添加person数据，然后添加person2时，同理。

数据库表数据如图：

![Center 1][]

下面测试一下unique是否起作用，

修改testSave（）方法代码：

/**
    	 * 保存数据
    	 * 
    	 * @throws HibernateException
    	 * @throws SerialException
    	 * @throws SQLException
    	 * @throws IOException
    	 */
    	@Test
    	public void testSave() throws HibernateException, SerialException,
    			SQLException, IOException {
    		Session session = null;
    		Transaction tx = null;
    		try {
    			session = HibernateUtil.getSession();
    			tx = session.beginTransaction();
    
    			IdCard idCard = new IdCard() ;
    			idCard.setCode("1525271000000000000") ;
    			
    			Person person = new Person() ;
    			person.setAge(23) ;
    			person.setName("张三") ;
    			person.setIdCard(idCard) ;
    
    			session.save(person) ;
    			
    			IdCard idCard2 = new IdCard() ;
    			idCard2.setCode("11011010000000000") ;
    			
    			Person person2 = new Person() ;
    			person2.setAge(24) ;
    			person2.setName("李四") ;
    			person2.setIdCard(idCard2) ;
    			
    			session.save(person2);
    			
    			Person person3 = new Person() ;
    			person3.setAge(25) ;
    			person3.setName("王五") ;
    			person3.setIdCard(idCard2) ;//依然使用idCard2身份信息
    			
    			session.save(person3) ;
    			
    
    			tx.commit();
    
    		} catch (HibernateException e) {
    			if (tx != null) {
    				tx.rollback();
    			}
    			e.printStackTrace();
    			throw e;
    		} finally {
    			HibernateUtil.closeSession();
    		}
    	}

运行testCreateDB，重新生成数据库表

运行testSave（）方法

![Center 2][]

报错了，说明unique起作用了

========================================================================

# 再说说双向的 #

新建一个java项目，名为：14hibernate\_double\_one\_to\_one\_foreign

项目结构如下：

![Center 3][]

其他的大部分和上面单向的是一样的，我只把不一样的列出来

IdCard实体类代码：

package com.robert.pojo;
    
    public class IdCard {
    
    	private int id ;
    	private String code ;//身份证号
    	private Person person ;//公民
    	
    	public Person getPerson() {
    		return person;
    	}
    	public void setPerson(Person person) {
    		this.person = person;
    	}
    	public int getId() {
    		return id;
    	}
    	public void setId(int id) {
    		this.id = id;
    	}
    	public String getCode() {
    		return code;
    	}
    	public void setCode(String code) {
    		this.code = code;
    	}
    }

IdCard.hbm.xml配置文件代码：

<?xml version="1.0"?>
    <!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.robert.pojo">
    	<class name="IdCard">
    		<id name="id">
    			<generator class="native"></generator>
    		</id>
    		<property name="code"></property>
    		<one-to-one name="person" property-ref="idCard"></one-to-one>
    	</class>
    </hibernate-mapping>

其中property-ref对应关系如图：

![Center 4][]

使用Junit4执行testCreateDB，重新生成数据库表

执行testSave（）执行保存方法，验证已成功，

下面说说获取方法

testGet()代码：

/**
    	 * 获取数据
    	 * @throws HibernateException
    	 * @throws SerialException
    	 * @throws SQLException
    	 * @throws IOException
    	 */
    	@Test
    	public void testGet() throws HibernateException, SerialException,
    			SQLException, IOException {
    		Session session = null;
    		Transaction tx = null;
    		try {
    			session = HibernateUtil.getSession();
    			tx = session.beginTransaction();
    
    			Person person = (Person)session.get(Person.class, 1) ;
    			System.out.println("pseron_name="+person.getName()+"----Idcard="+person.getIdCard().getCode());
    			
    			System.out.println("==================================");
    			
    			IdCard idCard = (IdCard)session.get(IdCard.class, 2) ;
    			System.out.println("idcard="+idCard.getCode()+"----person_name="+idCard.getPerson().getName());
    
    			tx.commit();
    
    		} catch (HibernateException e) {
    			if (tx != null) {
    				tx.rollback();
    			}
    			e.printStackTrace();
    			throw e;
    		} finally {
    			HibernateUtil.closeSession();
    		}
    	}

执行以后，控制台打印数据如下：

Hibernate: 
        select
            person0_.id as id1_1_0_,
            person0_.name as name2_1_0_,
            person0_.age as age3_1_0_,
            person0_.idcard_id as idcard_i4_1_0_ 
        from
            Person person0_ 
        where
            person0_.id=?
    Hibernate: 
        select
            idcard0_.id as id1_0_0_,
            idcard0_.code as code2_0_0_,
            person1_.id as id1_1_1_,
            person1_.name as name2_1_1_,
            person1_.age as age3_1_1_,
            person1_.idcard_id as idcard_i4_1_1_ 
        from
            IdCard idcard0_ 
        left outer join
            Person person1_ 
                on idcard0_.id=person1_.idcard_id 
        where
            idcard0_.id=?
    Hibernate: 
        select
            person0_.id as id1_1_0_,
            person0_.name as name2_1_0_,
            person0_.age as age3_1_0_,
            person0_.idcard_id as idcard_i4_1_0_ 
        from
            Person person0_ 
        where
            person0_.idcard_id=?
    pseron_name=张三----Idcard=1525271000000000000
    ==================================
    Hibernate: 
        select
            idcard0_.id as id1_0_0_,
            idcard0_.code as code2_0_0_,
            person1_.id as id1_1_1_,
            person1_.name as name2_1_1_,
            person1_.age as age3_1_1_,
            person1_.idcard_id as idcard_i4_1_1_ 
        from
            IdCard idcard0_ 
        left outer join
            Person person1_ 
                on idcard0_.id=person1_.idcard_id 
        where
            idcard0_.id=?
    idcard=11011010000000000----person_name=李四

解释：

等于号（=======）上面是从Person端获取person和idcard信息，一共打印了三条sql语句，且有重复；

等于号（=======）下面是从IdCard端获取perosn和idcard信息，只有一个sql语句。

由此可见，从idCard端效率会高一点

[Center]: /images/20220612/d6426d7900c14f1dabbd4244fd6dc9f8.png
[Hibernate]: http://blog.csdn.net/u011159417/article/details/75014665
[Hibernate 1]: http://blog.csdn.net/u011159417/article/details/75125902
[Center 1]: /images/20220612/32fa2e4900874b86b0bf243a01b5962c.png
[Center 2]: /images/20220612/5cc98418dfdf436ab54ce285a9e8416a.png
[Center 3]: /images/20220612/003f17b198e8442c9c202447a50e9f7a.png
[Center 4]: /images/20220612/a45e90173476433e9826f18a9b967ebf.png