Hibernate关系映射 --- 一对一实例分析(双向关联,是基于主键的)
2011-12-08 13:15
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Hibernate关系映射 --- 一对一实例分析
一 概念介绍
一对一的方式有两种,分为:
(1)基于主键的方式 --- 共用主键(Person --- IdCard)典型的一对一
没有增加额外的列
(2)基于外键的方式 --- 增加额外的一列
下面介绍一下第一中基于主键的实现
二 代码分析
(1)Person类
package com.hbsi.domain;
public class Person {
private int id;
private String name;
private IdCard idCard;//一个人对应一个IdCard
public Person() {
super();
// TODO Auto-generated constructor stub
}
public Person(int id, String name, IdCard idCard) {
super();
this.id = id;
this.name = name;
this.idCard = idCard;
}
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 IdCard getIdCard() {
return idCard;
}
public void setIdCard(IdCard idCard) {
this.idCard = idCard;
}
public String toString() {
return "Person [id=" + id + ", name=" + name + ", idCard=" + idCard
+ "]";
}
}
(2)IdCard类
package com.hbsi.domain;
import java.util.Date;
public class IdCard {
private int id;
private Date usefulLife;
private Person person; //一个IdCard只属于一个人
public IdCard() {
super();
// TODO Auto-generated constructor stub
}
public IdCard(int id, Date usefulLife, Person person) {
super();
this.id = id;
this.usefulLife = usefulLife;
this.person = person;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public Date getUsefulLife() {
return usefulLife;
}
public void setUsefulLife(Date usefulLife) {
this.usefulLife = usefulLife;
}
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
}
(3)在配置文件中配置Person类和IdCard类
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<!-- 配置文件 -->
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql:///demo</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">1234</property>
<!-- 方言 针对哪个数据库Mysql -->
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- 在程序运动的时候,增加自动创建表的属性,在程序终止 的时候销毁,但是在表格再次使用时,会重新建 -->
<property name="hibernate.hbm2ddl.auto">update</property>
<!-- 执行的sql语句显示出来 -->
<property name="hibernate.show_sql">true</property>
<!-- 指定映射文件的位置 -->
<mapping resource="com/hbsi/domain/Person.hbm.xml" />
<mapping resource="com/hbsi/domain/IdCard.hbm.xml" />
</session-factory>
</hibernate-configuration>
(4)person映射文件
<?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.hbsi.domain">
<class name="Person" table="person">
<id name="id" column="id">
<generator class="native" />
</id>
<property name="name" column="name" />
<!-- 一对一的映射 ,体现一对一的关联 -->
<one-to-one name="idCard"></one-to-one>
</class>
</hibernate-mapping>
(5)IdCard映射文件
<?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.hbsi.domain">
<class name="IdCard" table="id_card">
<id name="id" column="id">
<!-- 主键生成器,foreign ,参照主键生成器 -->
<generator class="foreign">
<param name="property">person</param>
</generator>
</id>
<property name="usefulLife" column="useful_life" />
<!-- 一对一的关联 -->
<one-to-one name="person"></one-to-one>
</class>
</hibernate-mapping>
注:需要注意的是idCard中的主键生成器,用的是foreign,并指定生产的id是根据person来设置的,这就是基于主键的one to one ,没有增加额外的列
(6)测试
package com.hbsi.test;
import java.util.Date;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.hbsi.domain.IdCard;
import com.hbsi.domain.Person;
import com.hbsi.hibernate.utils.HibernateUtil;
public class One2One {
public static void main(String[] args) {
add();
}
//保存的方法
static Person add() {
Session session = null;
Transaction transaction = null;
try {
session = HibernateUtil.getSession();
transaction = session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setUsefulLife(new Date());
Person person = new Person();
person.setName("Rose");
//必须彼此设置
person.setIdCard(idCard);
idCard.setPerson(person);
session.save(person);
session.save(idCard);
transaction.commit();
return person;
} finally {
if (session != null) {
session.close();
}
}
}
}
注:如果在设置的时候,只设置了person.setIdCard(idCard);而没有设置idCard.setPerson(person);会抛异常:
Exception in thread "main" org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property [com.hbsi.domain.IdCard.person]
at org.hibernate.id.ForeignGenerator.generate(ForeignGenerator.java:102)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:713)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:701)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:697)
at com.hbsi.test.One2One.add(One2One.java:34)
at com.hbsi.test.One2One.main(One2One.java:14)
原因是idCard的主键没有办法确定,所以必须都要写上
//通过人查询idCard
static Person query(int personId) {
Session session = null;
try {
session = HibernateUtil.getSession();
Person person = (Person) session.get(Person.class, personId);
System.out.println(person.getName()+":"+person.getIdCard().getUsefulLife());
return person;
} finally {
if (session != null) {
session.close();
}
}
}
注:如果在输出的时候用的是toString方法,可能会抛
Exception in thread "main" java.lang.StackOverflowError
错误,原因可能是因为Person和IdCard中都重写了toString方法,而在调用的时候,要先去调用IdCard中的toString方法,IdCard中的toString方法中又有一个Person类的对象要输出,所以又会去调用Person中的toString方法,来回反复,会抛内存溢出错误,解决的方法有三种:
(1) 去掉其中一个toString方法
(2) 去掉其中一个toString方法中的类的对象
(3) 输出的时候直接输出获取的方法,如getId(),getName(),而不用toString方法输出
一 概念介绍
一对一的方式有两种,分为:
(1)基于主键的方式 --- 共用主键(Person --- IdCard)典型的一对一
没有增加额外的列
(2)基于外键的方式 --- 增加额外的一列
下面介绍一下第一中基于主键的实现
二 代码分析
(1)Person类
package com.hbsi.domain;
public class Person {
private int id;
private String name;
private IdCard idCard;//一个人对应一个IdCard
public Person() {
super();
// TODO Auto-generated constructor stub
}
public Person(int id, String name, IdCard idCard) {
super();
this.id = id;
this.name = name;
this.idCard = idCard;
}
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 IdCard getIdCard() {
return idCard;
}
public void setIdCard(IdCard idCard) {
this.idCard = idCard;
}
public String toString() {
return "Person [id=" + id + ", name=" + name + ", idCard=" + idCard
+ "]";
}
}
(2)IdCard类
package com.hbsi.domain;
import java.util.Date;
public class IdCard {
private int id;
private Date usefulLife;
private Person person; //一个IdCard只属于一个人
public IdCard() {
super();
// TODO Auto-generated constructor stub
}
public IdCard(int id, Date usefulLife, Person person) {
super();
this.id = id;
this.usefulLife = usefulLife;
this.person = person;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public Date getUsefulLife() {
return usefulLife;
}
public void setUsefulLife(Date usefulLife) {
this.usefulLife = usefulLife;
}
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
}
(3)在配置文件中配置Person类和IdCard类
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<!-- 配置文件 -->
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql:///demo</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">1234</property>
<!-- 方言 针对哪个数据库Mysql -->
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- 在程序运动的时候,增加自动创建表的属性,在程序终止 的时候销毁,但是在表格再次使用时,会重新建 -->
<property name="hibernate.hbm2ddl.auto">update</property>
<!-- 执行的sql语句显示出来 -->
<property name="hibernate.show_sql">true</property>
<!-- 指定映射文件的位置 -->
<mapping resource="com/hbsi/domain/Person.hbm.xml" />
<mapping resource="com/hbsi/domain/IdCard.hbm.xml" />
</session-factory>
</hibernate-configuration>
(4)person映射文件
<?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.hbsi.domain">
<class name="Person" table="person">
<id name="id" column="id">
<generator class="native" />
</id>
<property name="name" column="name" />
<!-- 一对一的映射 ,体现一对一的关联 -->
<one-to-one name="idCard"></one-to-one>
</class>
</hibernate-mapping>
(5)IdCard映射文件
<?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.hbsi.domain">
<class name="IdCard" table="id_card">
<id name="id" column="id">
<!-- 主键生成器,foreign ,参照主键生成器 -->
<generator class="foreign">
<param name="property">person</param>
</generator>
</id>
<property name="usefulLife" column="useful_life" />
<!-- 一对一的关联 -->
<one-to-one name="person"></one-to-one>
</class>
</hibernate-mapping>
注:需要注意的是idCard中的主键生成器,用的是foreign,并指定生产的id是根据person来设置的,这就是基于主键的one to one ,没有增加额外的列
(6)测试
package com.hbsi.test;
import java.util.Date;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.hbsi.domain.IdCard;
import com.hbsi.domain.Person;
import com.hbsi.hibernate.utils.HibernateUtil;
public class One2One {
public static void main(String[] args) {
add();
}
//保存的方法
static Person add() {
Session session = null;
Transaction transaction = null;
try {
session = HibernateUtil.getSession();
transaction = session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setUsefulLife(new Date());
Person person = new Person();
person.setName("Rose");
//必须彼此设置
person.setIdCard(idCard);
idCard.setPerson(person);
session.save(person);
session.save(idCard);
transaction.commit();
return person;
} finally {
if (session != null) {
session.close();
}
}
}
}
注:如果在设置的时候,只设置了person.setIdCard(idCard);而没有设置idCard.setPerson(person);会抛异常:
Exception in thread "main" org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property [com.hbsi.domain.IdCard.person]
at org.hibernate.id.ForeignGenerator.generate(ForeignGenerator.java:102)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:713)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:701)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:697)
at com.hbsi.test.One2One.add(One2One.java:34)
at com.hbsi.test.One2One.main(One2One.java:14)
原因是idCard的主键没有办法确定,所以必须都要写上
//通过人查询idCard
static Person query(int personId) {
Session session = null;
try {
session = HibernateUtil.getSession();
Person person = (Person) session.get(Person.class, personId);
System.out.println(person.getName()+":"+person.getIdCard().getUsefulLife());
return person;
} finally {
if (session != null) {
session.close();
}
}
}
注:如果在输出的时候用的是toString方法,可能会抛
Exception in thread "main" java.lang.StackOverflowError
错误,原因可能是因为Person和IdCard中都重写了toString方法,而在调用的时候,要先去调用IdCard中的toString方法,IdCard中的toString方法中又有一个Person类的对象要输出,所以又会去调用Person中的toString方法,来回反复,会抛内存溢出错误,解决的方法有三种:
(1) 去掉其中一个toString方法
(2) 去掉其中一个toString方法中的类的对象
(3) 输出的时候直接输出获取的方法,如getId(),getName(),而不用toString方法输出
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