先贴上类文件Students.hbm.xml

 <?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2017-5-23 0:24:09 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
<class name="com.imooc.hibernate.Students" table="STUDENTS">
<id name="sid" type="int">
<column name="SID" />
<generator class="assigned" />
</id>
<property name="sname" type="java.lang.String">
<column name="SNAME" />
</property>
<property name="gender" type="java.lang.String">
<column name="GENDER" />
</property>
<property name="birthday" type="java.util.Date">
<column name="BIRTHDAY" />
</property>
<property name="address" type="java.lang.String">
<column name="ADDRESS" />
</property>
</class>
</hibernate-mapping>

其中<generator class="assigned" />:适用于自然主键,由java代码设置标识符。

  <generator class="assigned" />:适用于代理主键,hibernate自动生成标识符。

自然主键和代理主键请参考:http://blog.csdn.net/haiross/article/details/21388997

举个栗子:

students类:

 package com.imooc.hibernate;

 import java.util.Date;

 public class Students {

     private int sid;
private String sname;
private String gender;
private Date birthday;
private String address; public Students() {} public Students(int sid, String sname, String gender, Date birthday, String address) {
super();
this.sid = sid;
this.sname = sname;
this.gender = gender;
this.birthday = birthday;
this.address = address;
} @Override
public String toString() {
return "Students [sid=" + sid + ", sname=" + sname + ", gender=" + gender + ", birthday=" + birthday
+ ", address=" + address + "]";
} public int getSid() {
return sid;
} public void setSid(int sid) {
this.sid = sid;
} public String getSname() {
return sname;
} public void setSname(String sname) {
this.sname = sname;
} public String getGender() {
return gender;
} public void setGender(String gender) {
this.gender = gender;
} public Date getBirthday() {
return birthday;
} public void setBirthday(Date birthday) {
this.birthday = birthday;
} public String getAddress() {
return address;
} public void setAddress(String address) {
this.address = address;
}
}

hibernate.cfg.xml文件:

 <?xml version="1.0" encoding="UTF-8"?>
<!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.username">root</property>
<property name="connection.password">root</property>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate?useUnicode=true&amp;characterEncoding=UTF-8</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="hbm2ddl.auto">create</property> <mapping resource="com/imooc/hibernate/Students.hbm.xml"/>
</session-factory>
</hibernate-configuration>

测试类Students.java

 package com.icoom.test;
import static org.junit.Assert.fail; import java.util.Date; import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test; import com.imooc.hibernate.Students; public class StudentsTest { private SessionFactory sessionFactory;
private Session session;
private Transaction transaction; @Before
public void init() {
// 1.创建配置对象
Configuration config = new Configuration().configure();
// 2.创建服务注册对象
ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
// 3.创建会话工厂对象
sessionFactory = config.buildSessionFactory(serviceRegistry);
// 会话对象
session = sessionFactory.openSession();
// 开启事务
transaction = session.beginTransaction();
}
@After
public void destory() {
transaction.commit(); //提交事务
session.close(); //关闭session
sessionFactory.close();//关闭会话工厂
}
@Test
public void testSaveStudents() {
// 生成学生对象
// Students s = new Students(1, "老张", "男", new Date(), "山东");
Students s = new Students();
s.setSid(1);
s.setSname("老张");
s.setGender("男");
s.setBirthday(new Date());
s.setAddress("山东");
session.save(s);//保存对象进入数据库
}
}

数据库产生一条数据:

将hibernate.cfg.xml文件中的<property name="hbm2ddl.auto">create</property>改为<property name="hbm2ddl.auto">update</property>,然后再执行一次,就会报错。因为主键重复。

----------------------------------

将数据表删除,将Students.hbm.xml文件中的<generator class="assigned" />改成<generator class="native" />,然后再执行一次testSaveStudents()方法,会生成一条数据;再执行一次,Junit不会报错,而是插入了一条新数据:

以上就是assigned和native的区别。

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