Hibernate双向多对一实战

一 双向多对一生活举例

 

 

二 Grade.hbm.xml配置一对多关联关系

<?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>

        <class name="com.imooc.entity.Grade" table="grade">

                <id name="gid" column="gid" type="java.lang.Integer">

                        <generator class="increment"></generator>

                </id>

                <property name="gname" type="java.lang.String">

                        <column name="gname" length="20" not-null="true"></column>

                </property>

                <property name="gdesc">

                        <column name="gdesc"></column>

                </property>

                <!-- 配置一对多关联关系 -->

                <set name="students" table="student">

                        <key column="gid"></key>

                        <one-to-many class="com.imooc.entity.Student"/>

                </set>

        </class>

</hibernate-mapping>

 

三 Student.hbm.xml配置多对一关联关系

<?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>

        <class name="com.imooc.entity.Student" table="student">

                <id name="sid" column="sid" type="java.lang.Integer">

                        <generator class="increment"></generator>

                </id>

                <property name="sname" type="java.lang.String">

                        <column name="sname" length="20" not-null="true"></column>

                </property>

                <property name="sex">

                        <column name="sex"></column>

                </property>

                <!-- 配置多对一关联关系 -->

                <many-to-one name="grade" class="com.imooc.entity.Grade" column="gid" ></many-to-one>

                

        </class>

</hibernate-mapping>

 

四 测试代码

package com.imooc.test;

import org.hibernate.Session;

import org.hibernate.Transaction;

import com.imooc.entity.Grade;

import com.imooc.entity.Student;

import com.imooc.util.HibernateUtil;

/*

* 单向多对一（学生--->班级）

*/

public class Test02 {

    public static void main(String[] args) {

        save();

    }

    

    //保存

    public static void save(){

        Grade g=new Grade("Java一班","Java软件开发一班");

        Student stu1=new Student("慕女神", "女");

        Student stu2=new Student("小慕慕", "男");

        

        //设置关联关系

        g.getStudents().add(stu1);

        g.getStudents().add(stu2);

        stu1.setGrade(g);

        stu2.setGrade(g);

        

        Session session=HibernateUtil.getSession();

        Transaction tx=session.beginTransaction();

        session.save(g);

        session.save(stu1);

        session.save(stu2);

        tx.commit();

        HibernateUtil.closeSession(session);

    }

}

 

五 测试结果

Hibernate: select max(gid) from grade

Hibernate: select max(sid) from student

Hibernate: insert into grade (gname, gdesc, gid) values (?, ?, ?)

Hibernate: insert into student (sname, sex, gid, sid) values (?, ?, ?, ?)

Hibernate: insert into student (sname, sex, gid, sid) values (?, ?, ?, ?)

Hibernate: update student set gid=? where sid=?

Hibernate: update student set gid=? where sid=?

从后台输出来看，多余了两条update语句。