java鬼混笔记：Hibernate：3、一对一关系之外键单向和双向关联

这次的笔记是 一对一外键关联，包含单向和双向，用 人和身份证来举例，一个人一个身份证。直接上代码，代码里头有注释说明。gogogo

单向关联：(person有card,card中没有person)

Person.java

package com.ywj.TestHibernate.e;import java.io.Serializable;public class Person implements Serializable{/** *  */private static final long serialVersionUID = -3189538608590684635L;private Long id;private String name;private Card card;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Card getCard() {return card;}public void setCard(Card card) {this.card = card;}}

Person.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.ywj.TestHibernate.e"><class name="Person" table="person" ><id name="id" column="id"><generator class="identity" /><!-- 自增长 外键关联了， 和主键id没关系 --></id><property name="name" column="name" type="java.lang.String"/><!-- 这里用many-to-one，对多一，但是这个多对一要设置成独立的，独立了也是就意味着只有一个person对应一个card --><many-to-one  name="card"  column="card" unique="true" cascade="all" fetch="join"/>

<!-- unique="true":person表中的字段card是独立的唯一的，对应card表中的ID --><!-- fetch="join" 的意思是当我查询person表时，它会left join card 表去查询,同时加载card表信息，就只执行一条sql,也就是查询person或者通过person查询card要1条sql 但是lazy懒加载会失效fetch="select" 的意思是当我查询person表时，它只查person表，当我们从person中获取card时他会重新执行一条sql 去从card表中查一次。也就是通过person查询card要2条sql --></class></hibernate-mapping>

Card.java

package com.ywj.TestHibernate.e;import java.io.Serializable;public class Card implements Serializable{private static final long serialVersionUID = 5451125658782668299L;private Long id;private String number;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}}

Card.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.ywj.TestHibernate.e">

<!--普通的创建就行--><class name="Card" table="card" ><id name="id" column="id"><generator class="identity" /></id><property name="number" column="number" type="java.lang.String"/></class></hibernate-mapping>

Test.java

package com.ywj.TestHibernate.test;import org.hibernate.Session;import org.hibernate.Transaction;import com.ywj.TestHibernate.e.Card;import com.ywj.TestHibernate.e.Person;public class Test {public static void main(String[] args) {Session s = HibernateUtils.getCurrentSession();Transaction t  = null;try {t = s.beginTransaction();// 添加/*Card c = new Card();c.setNumber("xxxxxxxxxxxx");Person p = new Person();p.setName("name");p.setCard(c);s.save(p);s.save(c);t.commit();*/// 查询/*Person p = (Person) s.load(Person.class, 1L);System.out.println(p.getName());Card c = p.getCard();System.out.println(c.getNumber());*///删除　连card也删除 因为person.hbm.xml配置了cascade="all",person的任何的操作都会影响表card/*Person p = (Person) s.load(Person.class, 2L);s.delete(p);t.commit();*/} catch (Exception e) {e.printStackTrace();t.rollback();} finally {s.close();}}}

接下来是 

双向关联

Person.java

package com.ywj.TestHibernate.e;import java.io.Serializable;public class Person implements Serializable{/** *  */private static final long serialVersionUID = -3189538608590684635L;private Long id;private String name;private Card card;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Card getCard() {return card;}public void setCard(Card card) {this.card = card;}}

Person.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.ywj.TestHibernate.e"><class name="Person" table="person" ><id name="id" column="id"><generator class="identity" /><!-- 自增长 外键关联了， 和主键id没关系 --></id><property name="name" column="name" type="java.lang.String"/><!-- 问题来了， 这里和一对一主键关联不一样，这里用many-to-one，对多一，但是这个多对一要设置成独立的，独立了也是就意味着只有一个person对应一个card --><many-to-one  name="card"  column="card" unique="true"/><!-- unique="true":person表中的字段是独立的，对应card表中的ID --></class></hibernate-mapping>

Card.java

package com.ywj.TestHibernate.e;import java.io.Serializable;public class Card implements Serializable{private static final long serialVersionUID = 5451125658782668299L;private Long id;private String number;private Person person;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}public Person getPerson() {return person;}public void setPerson(Person person) {this.person = person;}}

Card.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.ywj.TestHibernate.e"><class name="Card" table="card" ><id name="id" column="id"><generator class="identity" /></id><property name="number" column="number" type="java.lang.String"/><!-- card这里使用one-to-one 证明和person是一对一的，核心是property-ref="card",意思是card怎么和person形成一对一？card是通过person(class="Person")来找到person.card属性（property-ref="card" ：参照person中的card属性，这个有点像spring...） --><one-to-one name="person" class="Person" property-ref="card"/></class></hibernate-mapping>

Test.java

package com.ywj.TestHibernate.test;import org.hibernate.Session;import org.hibernate.Transaction;import com.ywj.TestHibernate.e.Card;import com.ywj.TestHibernate.e.Person;public class Test {public static void main(String[] args) {Session s = HibernateUtils.getCurrentSession();Transaction t  = null;try {t = s.beginTransaction();// 添加/*Card c = new Card();c.setNumber("xxxxxxxxxxxx");Person p = new Person();p.setName("name");p.setCard(c);s.save(p);s.save(c);t.commit();*/// 查询/*Person p = (Person) s.load(Person.class, 1L);System.out.println(p.getName());Card c = p.getCard();System.out.println(c.getNumber());System.out.println("////////////////");Card c2 = (Card) s.load(Card.class, 3L);System.out.println(c2.getNumber());System.out.println(c2.getPerson().getName());*///删除　连card也删除 因为person.hbm.xml配置了cascade="all",person的任何的操作都会影响表card/*Person p = (Person) s.load(Person.class, 2L);s.delete(p);t.commit();*/} catch (Exception e) {e.printStackTrace();t.rollback();} finally {s.close();}}}