hibernate基础05：关联关系1对多

1、Java实体bean类

package com.project.pojo;

import java.io.Serializable;

public class Student implements Serializable{
    private int id;
    private String name;
    private int age;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
}

package com.project.pojo;

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

public class Classes implements Serializable{
    private int id;
    private String name;
    private String address;
    private Set<Student> student = new HashSet<Student>();
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public Set<Student> getStudent() {
        return student;
    }
    public void setStudent(Set<Student> student) {
        this.student = student;
    }
    
    public void setStudent(Student student) {
        this.getStudent().add(student);
    }
    
    
}

2、hbm.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<!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.project.pojo">
    <class name="Classes" table="t_class">
        <id name="id" column="id" type="int">
            <generator class="native"></generator>
        </id>
        <property name="name" />
        <property name="address" />
        <!-- 1对多的关联name为属性名 -->
        <set name="student">
            <!-- column指定外键名 -->
            <key column="class_id"></key>
            <!-- 指定多端的类 -->
            <one-to-many class="Student"/>
        </set>
    </class>

</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- package指定类所在的包，如果不指定，那么在指定class的name时，需要指定完全限定名 -->
<hibernate-mapping package="com.project.pojo">
    <class name="Student" table="t_student">
        <id name="id">
            <generator class="native"></generator>
        </id>
        <property name="name" />
        <property name="age" />
    </class>

</hibernate-mapping>

3、hibernate.cfg.xml配置

<?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>
        <!-- 1、数据库连接信息 -->
        <!-- 指定数据方言 -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://192.168.1.59:3306/hibernate?characterEncoding=UTF8</property>
        <property name="connection.username">root</property>
        <property name="connection.password">1234</property>
        
        <!-- 2、通用配置信息 -->
        <!-- 打印sql语句 -->
        <property name="show_sql">true</property>
        <!-- 格式化sql语句 -->
        <property name="format_sql">true</property>
        
        <!-- 
            hbm2ddl.auto 该属性用于配置是否将映射信息转换为ddl
            create 每次执行都会先删除后再创建表，用于测试
            update 检查数据库表是否存在，如果不存在则先创建表，项目中通常上线使用
         -->
        <!-- <property name="hbm2ddl.auto">update</property> -->
        <!-- 映射文件信息 -->
        <mapping resource="com/project/pojo/Classes.hbm.xml" />
        <mapping resource="com/project/pojo/Student.hbm.xml" />
    </session-factory >
</hibernate-configuration>

4、测试

package com.project.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.project.pojo.Classes;
import com.project.pojo.Student;
import com.project.util.HibernateUtil;

public class HibernateTest {
    Session session = null;
    Transaction ts = null;
    
    @Before
    public void setUp(){
        session = HibernateUtil.getSession();
        ts = session.beginTransaction();
    }
    
    @After
    public void tearDown(){
        HibernateUtil.closeSession();
    }
    
    
    @Test
    public void testCreateDB(){
        Configuration cfg = new Configuration().configure();
        //使得hibernate映射信息转换为数据库识别的dll语言
        SchemaExport se = new SchemaExport(cfg);
        //第一个参数：是否打印dll语句
        //第二个参数：是否将dll到数据库中执行
        se.create(true, true);
    }
    
    /**
     * 一对多关联时保存数据会多出n条更新语句，效率比较低
     * 一般不用一对多管理数据
     */
    @Test
    public void testSave(){
        try {
            Classes c1 = new Classes();
            c1.setName("一年级");
            c1.setAddress("B-1栋");
            
            Classes c2 = new Classes();
            c2.setName("二年级");
            c2.setAddress("B-2栋");
            
            Student s1 = new Student();
            s1.setName("张三");
            s1.setAge(20);
            
            Student s2 = new Student();
            s2.setName("李四");
            s2.setAge(21);
            
            Student s3 = new Student();
            s3.setName("哈哈狗");
            s3.setAge(19);
            
            session.save(s1);
            session.save(s2);
            session.save(s3);
            
            //关联关系由1端控制
            c1.setStudent(s1);
            c1.setStudent(s3);
            c2.setStudent(s2);
            
            session.save(c1);
            session.save(c2);
            
            ts.commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(ts!=null) ts.rollback();
        }
    
    }
    
    @Test
    public void testSelect(){
        Classes c = (Classes) session.get(Classes.class, 1);
        System.out.println(c.getName()+"	"+c.getAddress());
        System.out.println("------------------");
        for(Student stu : c.getStudent()){
            System.out.println(stu.getName()+"	"+stu.getAge());
        }
        
    }
}