hibernate中的many-to-one的例子

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hibernate

Hibernate MySQL log4j SQL XML

sql 代码

由于最近在学习hibernate时,对many-to-one的配置总是出错今天根据多方资料终于把他给弄好拉,现把代码全部粘贴在这里,以便以后在做参考

java 代码

//person类
package com.tyq.hibernate.db;
public class Person implements java.io.Serializable {
private int id;
private String name;
private String password;
/** default constructor */
public Person() {
}
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return this.password;
}
public void setPassword(String password) {
this.password = password;
}
}

java 代码

//Sister类
package com.tyq.hibernate.db;
public class Sister implements java.io.Serializable {
private Integer id;
private String name;
private Person person;
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
public Sister() {
}
public Sister(Integer id, String name, Integer personId) {
this.id = id;
this.name = name;
}
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
}

下面是它们对应的映射文件

xml 代码

<?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.tyq.hibernate.db">
<class name="Sister" table="sister" catalog="mldn">
<id name="id" type="java.lang.Integer" unsaved-value="null">
<column name="id" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="name" length="40" not-null="true" unique="true" />
</property>
<many-to-one name="person" column="person_id" class="Person"/>
</class>
</hibernate-mapping>

<?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>
<class name="com.tyq.hibernate.db.Person" table="person" catalog="mldn">
<id name="id" type="java.lang.Integer">
<column name="id" length="20" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="name" length="20" not-null="true" />
</property>
<property name="password" type="java.lang.String">
<column name="password" length="20" />
</property>
</class>
</hibernate-mapping>

假设一个人会有很多Sister而这里简单起见把这种关联设置为单向

下面是测试类

java 代码

package com.tyq.test;
import java.util.Iterator;
import junit.framework.TestCase;
import org.hibernate.Session;
import com.tyq.hibernate.HibernateSessionFactory;
import com.tyq.hibernate.db.Person;
import com.tyq.hibernate.db.Sister;
public class TestHibernate extends TestCase {
Session session = null;
protected void setUp() throws Exception {
session = HibernateSessionFactory.getSession();
}
protected void tearDown() throws Exception {
HibernateSessionFactory.closeSession();
}
public void testAA()
{
Person p = new Person();
Sister s = new Sister();
Iterator it = session.createQuery("FROM Sister").iterate();
while(it.hasNext())
{
s = (Sister)it.next();
System.out.println("person:"+s.getPerson().getName()+"Sister:"+s.getName());
}
}
}

事先在数据库中已经已经存放了测试用数据

它们分别是

sql 代码

mysql> use mldn;
Database changed
mysql> select * from person;
+----+----------------+----------+
| id | name | password |
+----+----------------+----------+
| 1 | liuqinglaityq | hello |
| 2 | liuqinglaityq2 | hello |
| 3 | liuqinglaityq3 | hello |
+----+----------------+----------+
3 rows in set (0.00 sec)
mysql> select * from sister;
+----+-------------+-----------+
| id | name | person_id |
+----+-------------+-----------+
| 1 | liuahijuan | 1 |
| 2 | liuahijuan1 | 2 |
+----+-------------+-----------+
2 rows in set (0.00 sec)

运行时得到的结果是

sql 代码

log4j:WARN Please initialize the log4j system properly.
Hibernate: select sister0_.id as col_0_0_ from mldn.sister sister0_
Hibernate: select sister0_.id as id1_0_, sister0_.name as name1_0_, sister0_.person_id as person3_1_0_ from mldn.sister sister0_ where sister0_.id=?
Hibernate: select person0_.id as id0_0_, person0_.name as name0_0_, person0_.password as password0_0_ from mldn.person person0_ where person0_.id=?
person:liuqinglaityqSister:liuahijuan
Hibernate: select sister0_.id as id1_0_, sister0_.name as name1_0_, sister0_.person_id as person3_1_0_ from mldn.sister sister0_ where sister0_.id=?
Hibernate: select person0_.id as id0_0_, person0_.name as name0_0_, person0_.password as password0_0_ from mldn.person person0_ where person0_.id=?
person:liuqinglaityq2Sister:liuahijuan1

从这里可以看出hibernate只是在应用时才生成对象用这样的形式来达到优化性能的效果.

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