班级-学生一对多映射实现(单向)
Class.java
package com.java1234.model;
public class Class {
private long id;
private String name;
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;
}
}
Student.java
package com.java1234.model;
public class Student {
private long id;
private String name;
private Class c;
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 Class getC() {
return c;
}
public void setC(Class c) {
this.c = c;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
}
映射文件:Class.hbm.xml
<?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.java1234.model">
<class name="Class" table="t_class">
<id name="id" column="classId">
<generator class="native"></generator>
</id>
<property name="name" column="className"></property>
</class>
</hibernate-mapping>
Student.hbm.xml
<?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.java1234.model">
<class name="Student" table="t_student">
<id name="id" column="stuId">
<generator class="native"></generator>
</id>
<property name="name" column="stuName"></property>
<many-to-one name="c" column="classId" class="com.java1234.model.Class" cascade="save-update"></many-to-one>
</class>
</hibernate-mapping>
配置文件:hibernate.cfg.xml
<?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>
<!--数据库连接设置 -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<!-- 方言 -->
<property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
<!-- 控制台显示SQL -->
<property name="show_sql">true</property>
<!-- 自动更新表结构 -->
<property name="hbm2ddl.auto">update</property>
<mapping resource="com/java1234/model/Student.hbm.xml"/>
<mapping resource="com/java1234/model/Class.hbm.xml"/>
</session-factory>
</hibernate-configuration>
单元测试:StudentTest3.java
package com.java1234.service;
import static org.junit.Assert.*;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import com.java1234.model.Class;
import com.java1234.model.Student;
import com.java1234.util.HibernateUtil;
public class StudentTest3 {
private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
private Session session;
@Before
public void setUp() throws Exception {
session=sessionFactory.openSession(); // 生成一个session
session.beginTransaction(); // 开启事务
}
@After
public void tearDown() throws Exception {
session.getTransaction().commit(); // 提交事务
session.close(); // 关闭session
}
@Test
public void testSaveClassAndStudent() {
Class c=new Class();
c.setName("08计本");
session.save(c);
Student s1=new Student();
s1.setName("张三");
s1.setC(c);
Student s2=new Student();
s2.setName("李四");
s2.setC(c);
session.save(s1);
session.save(s2);
}
@Test
public void testSaveClassAndStudentWithCascade() {
Class c=new Class();
c.setName("08计本");
Student s1=new Student();
s1.setName("张三");
s1.setC(c);
Student s2=new Student();
s2.setName("李四");
s2.setC(c);
session.save(s1);
session.save(s2);
}
}
在<many-to-one>这端,cascade 默认是”none”,假如我们希望在持久化多的一端的时候,自动级 联保存和更新一的一端,我们可以把 cascade 设置成”save-update”;
就像上面的那两个方法:testSaveClassAndStudent(), testSaveClassAndStudentWithCascade(),前面那个方法是没有加上
cascade="save-update"的,所以加上了session.save(c);因为不会自动级联保存班级信息。
还有值得一说的是,在testSaveClassAndStudentWithCascade()中,s1,s2对象放在了session缓存中是持久化对象,c对象没有放在其中,是临时对象。
运行之后数据库的 结果
t_student表
t_class表