Hibernate 关联映射

实体之间的关系
　　关联，聚合，依赖，组合，继承

关系的类型：
　　一对多
　　多对一
　　一对一
　　多对多

---

　　学生表和年级表：

--学生表
create table student(
       stuno number(4) primary key,
       name varchar2(20) not null,
       gradeid number(4)

)
--年级表
create table grade(
       gradeid number(4) primary key,
       gradename varchar2(20) not null

)

当一对多和多对一关系组合就是双向关联了

　　所以整合在一起写了个添加数据和删除外键表的 级联代码

　　1.建立对象

　　　　student:　　　　

package entity;

import java.io.Serializable;
/**
 * 学生实体类
 * @author Administrator
 *
 */
public class Student implements Serializable{
    private Integer stuno;
    private String name;
    private Integer gradeid;
    //学生与年级属于多多对一的关系
    private Grade grade;
    
    public Student(){}
    public Integer getStuno() {
        return stuno;
    }
    public void setStuno(Integer stuno) {
        this.stuno = stuno;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getGradeid() {
        return gradeid;
    }
    public void setGradeid(Integer gradeid) {
        this.gradeid = gradeid;
    }
    public Grade getGrade() {
        return grade;
    }
    public void setGrade(Grade grade) {
        this.grade = grade;
    }
    
    
}

　　　　grade:

package entity;

import java.io.Serializable;
import java.util.Set;
/**
 * 年级实体类
 * @author Administrator
 *
 */
public class Grade implements Serializable{
    //年级编号
    private Integer gradeid;
    //年级
    private String gradename;
    
    private Set<Student> stu;
    
    public Grade(){}
    
    public Set<Student> getStu() {
        return stu;
    }

    public void setStu(Set<Student> stu) {
        this.stu = stu;
    }

    public Integer getGradeid() {
        return gradeid;
    }
    public void setGradeid(Integer gradeid) {
        this.gradeid = gradeid;
    }
    public String getGradename() {
        return gradename;
    }
    public void setGradename(String gradename) {
        this.gradename = gradename;
    }
    
    
    
}

　　2.建立对象之间的关系

<!--grade表-->
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping
    package="entity">
    
    <class name="Grade" table="grade" dynamic-update="true">
        <id name="gradeid" type="integer">
            <generator class="assigned">
                
            </generator>
        </id>
        <property name="gradename" type="java.lang.String" />
        <set name="stu" cascade="all">
            <key column="gradeid"/>
            <one-to-many class="Student"/>
        </set>
        
    </class>
</hibernate-mapping>


<!--student表-->
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping
    package="entity">
    
    <class name="Student" table="student" dynamic-update="true">
        <id name="stuno" type="integer">
            <generator class="sequence">
                <param name="sequence">seq_student</param>
            </generator>
        </id>
        <property name="name" type="java.lang.String" />
        
        <!-- 多对一关系 -->
        <many-to-one name="grade" class="Grade">
            <column name="gradeid"></column>
        </many-to-one>
    </class>
</hibernate-mapping>

　　3.配置hibernate

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

<hibernate-configuration>
    <session-factory>
        
        <!-- 指定oracle对应得dialect -->
        <property name="dialect">
            org.hibernate.dialect.Oracle10gDialect
        </property>
        <!-- 数据库jdbc驱动 -->
        <property name="connection.driver_class">
            oracle.jdbc.driver.OracleDriver
        </property>
        
        <!-- 数据库url -->
        <property name="connection.url">
            jdbc:oracle:thin:@localhost:1521:XE
        </property>
        
        <!-- 用户名 -->
        <property name="connection.username">super_user</property>
        <!-- 用户密码 -->
        <property name="connection.password">abc123</property>
        
        <!-- session范围和上下文 -->
        <property name="current_session_context_class">thread</property>
        <!-- 是否在运行期间生成的SQL输出到日志以供调试 -->
        <property name="show_sql">true</property>
        <!-- 是否格式化sql -->
        <property name="format_sql">true</property>
        <!-- 根据映射文件自动生成表-->
        <property name="hbm2ddl.auto">update</property> 
        <!-- 映射 -->
        <mapping resource="entity/Grade.hbm.xml" />
        <mapping resource="entity/Student.hbm.xml" />
        
    </session-factory>
</hibernate-configuration>

　　上面配置文件中出现了三个新的配置节点，和新的节点属性：

　　　1.<set name="stu" cascade="all">   --name指定对象中属性名   cascade：级联 ————》all/none/save-update/delete/都是字面意思

　　　　<key column="gradeid"/>　　　　--指定两个对象关联的主键
　　　　<one-to-many class="Student"/>　　--这里是个一对多关系的实体类配置 ，因为我在mapping中配置了package所以这里只写类名
　　　</set>

　　　2.<many-to-one name="grade" class="Grade"> --指定对象中处于“一”关系的属性名，并且指明类名

　　　　<column name="gradeid"></column>　　　　--制定关联的主键
　　　　</many-to-one>

　　　3.<property name="hbm2ddl.auto">update</property>   --指定操作类型

　　　　　　#hibernate.hbm2ddl.auto create-drop  
　　　　　　#hibernate.hbm2ddl.auto create
　　　　　　#hibernate.hbm2ddl.auto update
　　　　　　#hibernate.hbm2ddl.auto validate

　　

　　测试代码：

　　　　

package dao;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import entity.Grade;
import entity.Student;

/**
 * 多对一关系联动练习
 * @author Administrator
 *
 */
public class StudentDao {
    //打开配置
    SessionFactory factory=new Configuration().configure().buildSessionFactory();
    Session session=null;
    
    public static void main(String[] args) {
        StudentDao stu=new StudentDao();
        try {
            //stu.update();
            stu.del();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            
        }
    }
    /**
     * 新增
     */
    public void update() throws Exception{
        session=factory.openSession();
        session.beginTransaction();
        //Grade grade=(Grade)session.get(Grade.class, 1);
        
        Student student=new Student();
        Grade grade=new Grade();
        grade.setGradeid(1);
        grade.setGradename("一年级");
        session.save(grade);
        student.setName("小明");
        student.setGrade(grade);
        session.save(student);
        session.getTransaction().commit();
        System.out.println("成功！");
        
        session.close();
    }
    /**
     * 删除
     */
    public void del(){
        session=factory.openSession();
        session.beginTransaction();
        //Student student=(Student)session.get(Student.class, 5);
        //级联删除
        Grade grade=(Grade)session.get(Grade.class, 1);
        session.delete(grade);
        //session.delete(student);
        session.getTransaction().commit();
        System.out.println("成功！");
        
        session.close();
    }
}

　　　在代码中遇到的问题：http://www.cnblogs.com/gcs1995/p/4139422.html