Hibernate单向多对一实战

一 单向多对一生活举例

 

 

二 实现方式

多对一的关系和关系数据库中的外键参照关系最匹配，即在多方的表中的一个外键参照一方表的主键。

通过在多方持有一方的引用实现，需要在“多”的一端使用<many-to-one>配置。

 

三 单向多对一的配置

1 Student.java

package com.imooc.entity;

 

import java.io.Serializable;

 

public class Student implements Serializable {

        private int sid;

        private String sname;

        private String sex;

        // 在多方定义一个一方的引用

        private Grade grade;

 

        public Grade getGrade() {

                return grade;

        }

 

        public void setGrade(Grade grade) {

                this.grade = grade;

        }

 

        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 getSex() {

                return sex;

        }

 

        public void setSex(String sex) {

                this.sex = sex;

        }

 

        public Student() {

                super();

        }

 

        public Student(String sname, String sex) {

                super();

                this.sname = sname;

                this.sex = sex;

        }

 

}

 

2 Student.hbm.xml配置

<?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 测试添加学生信息

1 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

        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);

    }

}

2 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 (?, ?, ?, ?)