Hibernate(四)一对多映射-优快云博客

本文介绍使用Hibernate框架实现学生与班级之间的关系映射，包括数据库表创建、实体类定义、映射文件配置及基本的增删改查操作。

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数据库表创建

create table grade
(
    gid int primary key,
    gname varchar(20) not null,
    gdesc varchar(50)
);

create table student
(
    sid int primary key,
    sname varchar(20) not null,
    sex char(2),
    gid int
);

alter table student add constraint fk_student_gid foreign key (gid)
references grade(gid);

Grade年级class

package com.imooc.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

public class Grade implements Serializable {
    private int gid;
    private String gname;
    private String gdesc;
    //在一方定义一个多方的集合
    private Set<Student> students = new HashSet<Student>();
    public int getGid() {
        return gid;
    }
    public void setGid(int gid) {
        this.gid = gid;
    }
    public String getGname() {
        return gname;
    }
    public void setGname(String gname) {
        this.gname = gname;
    }
    public String getGdesc() {
        return gdesc;
    }
    public void setGdesc(String gdesc) {
        this.gdesc = gdesc;
    }
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
    public Grade() {
        super();
    }

    public Grade(String gname, String gdesc) {
        super();
        this.gname = gname;
        this.gdesc = gdesc;
    }

    public Grade(int gid, String gname, String gdesc, Set<Student> students) {
        super();
        this.gid = gid;
        this.gname = gname;
        this.gdesc = gdesc;
        this.students = students;
    }

}

学生student class

package com.imooc.entity;

import java.io.Serializable;

public class Student implements Serializable {
    private int sid;
    private String sname;
    private String sex;
    private 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 Grade getGrade() {
        return grade;
    }
    public void setGrade(Grade grade) {
        this.grade = grade;
    }
    public Student() {
        super();
    }
    public Student(String sname, String sex) {
        super();
        this.sname = sname;
        this.sex = sex;
    }

}

Grade.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 >

    <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>
        <!-- 配置单向的一对多关系  inverse="true" 由多的一方进行   cascade级联操作保存one的一方会保存many的一方-->
        <set name="students" table="student" cascade="save-update" inverse="true">
            <!--指定关联的外键列  -->
            <key column="gid"></key>
            <one-to-many class="com.imooc.entity.Student"/>
        </set>
    </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 >

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


</hibernate-mapping>

HibernateUtil.java class

package com.imooc.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

    private static SessionFactory sessionFactory;
    private static Session session;

    static{
        Configuration config = new Configuration().configure();
        //ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
        StandardServiceRegistry ssr = new StandardServiceRegistryBuilder().applySettings(config.getProperties()).build();
        sessionFactory = config.buildSessionFactory(ssr);
    }

    //获取SessionFactory
    public static SessionFactory getSessionFactory(){
        return sessionFactory;
    }

    //获取Session
    public static Session getSession(){
        session = sessionFactory.openSession();
        return session;
    } 

    //关闭session
    public static void closeSession(Session session){
        if(session!=null){
            session.close();
        }
    }

}

Hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
  <session-factory>
    <!-- Database connection settings -->
    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="connection.url">jdbc:mysql:///imooc?useUnicode=true&amp;characterEncoding=UTF-8</property>
    <property name="connection.username">root</property>
    <property name="connection.password">123456</property>

    <!-- SQL dialect -->
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

    <!-- Enable Hibernate's automatic session context management -->
    <property name="current_session_context_class">thread</property>

    <!-- Echo all executed SQL to stdout -->
    <property name="show_sql">true</property>

    <!-- Drop and re-create the database schema on startup -->
    <property name="hbm2ddl.auto">update</property>

    <mapping resource="com/imooc/entity/Grade.hbm.xml"/>
    <mapping resource="com/imooc/entity/Student.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

增删改查

package com.imooc.entity;

import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.imooc.util.HibernateUtil;

public class Test {

    public static void main(String[] args) {
        add();
        //findStudentsByGrade();
        //update();
        //delete();
    }

    //将学生添加到班级
    public static void add(){
        Grade g = new Grade("Java四班","Java软件开发四班");
        Student stu1 = new Student("张三2","男");
        Student stu2 = new Student("慕女神2","女");

        //如果希望在学生表中添加对应的班级编号，
        g.getStudents().add(stu1);
        g.getStudents().add(stu2);

        Session session = HibernateUtil.getSession();
        Transaction tx = session.beginTransaction();
        session.save(g);
        //设置cascade后会自动保存
        //session.save(stu1);
        //session.save(stu2);
        tx.commit();
        HibernateUtil.closeSession(session);
    }

    public static void findStudentsByGrade(){

        Session session = HibernateUtil.getSession();
        Grade grade = (Grade) session.get(Grade.class, 1);
        System.out.println(grade.getGname()+","+grade.getGdesc());

        Set<Student> students= grade.getStudents();
        for(Student stu:students){
            System.out.println(stu.getSname()+","+stu.getSex());
        }
    }

    public static void update(){
        Grade g = new Grade("Java二班","Java软件开发二班");

        Session session = HibernateUtil.getSession();
        Transaction tx = session.beginTransaction();

        Student stu = (Student) session.get(Student.class,1);
        g.getStudents().add(stu);
        session.save(g);
        tx.commit();
        HibernateUtil.closeSession(session);

    }

    public static void delete(){
        Session session = HibernateUtil.getSession();
        Transaction tx = session.beginTransaction();
        Student stu = (Student) session.get(Student.class, 2);
        session.delete(stu);
        tx.commit();
        HibernateUtil.closeSession(session);
    }
}

package com.imooc.entity;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.imooc.util.HibernateUtil;

public class Test02 {

    public static void main(String[] args) {
        save();
    }

    public static void save(){
        Grade g = new Grade("Java三班", "java软件开发三班");
        Student stu1 =new Student("慕女生","女");
        Student stu2 =new Student("小穆穆","男");
        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);
    }

}