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：

 1 --学生表
 2 create table student(
 3        stuno number(4) primary key,
 4        name varchar2(20) not null,
 5        gradeid number(4)
 6 
 7 )
 8 --年级表
 9 create table grade(
10        gradeid number(4) primary key,
11        gradename varchar2(20) not null
12 
13 )

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:　　　　

 1 package entity;
 2 
 3 import java.io.Serializable;
 4 /**
 5  * 学生实体类
 6  * @author Administrator
 7  *
 8  */
 9 public class Student implements Serializable{
10     private Integer stuno;
11     private String name;
12     private Integer gradeid;
13     //学生与年级属于多多对一的关系
14     private Grade grade;
15     
16     public Student(){}
17     public Integer getStuno() {
18         return stuno;
19     }
20     public void setStuno(Integer stuno) {
21         this.stuno = stuno;
22     }
23     public String getName() {
24         return name;
25     }
26     public void setName(String name) {
27         this.name = name;
28     }
29     public Integer getGradeid() {
30         return gradeid;
31     }
32     public void setGradeid(Integer gradeid) {
33         this.gradeid = gradeid;
34     }
35     public Grade getGrade() {
36         return grade;
37     }
38     public void setGrade(Grade grade) {
39         this.grade = grade;
40     }
41     
42     
43 }

Student

　　　　grade:

 1 package entity;
 2 
 3 import java.io.Serializable;
 4 import java.util.Set;
 5 /**
 6  * 年级实体类
 7  * @author Administrator
 8  *
 9  */
10 public class Grade implements Serializable{
11     //年级编号
12     private Integer gradeid;
13     //年级
14     private String gradename;
15     
16     private Set<Student> stu;
17     
18     public Grade(){}
19     
20     public Set<Student> getStu() {
21         return stu;
22     }
23 
24     public void setStu(Set<Student> stu) {
25         this.stu = stu;
26     }
27 
28     public Integer getGradeid() {
29         return gradeid;
30     }
31     public void setGradeid(Integer gradeid) {
32         this.gradeid = gradeid;
33     }
34     public String getGradename() {
35         return gradename;
36     }
37     public void setGradename(String gradename) {
38         this.gradename = gradename;
39     }
40     
41     
42     
43 }

grade

　　2.建立对象之间的关系

 1 <!--grade表-->
 2 <?xml version="1.0"?>
 3 <!DOCTYPE hibernate-mapping PUBLIC 
 4     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 5     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 6 
 7 <hibernate-mapping
 8     package="entity">
 9     
10     <class name="Grade" table="grade" dynamic-update="true">
11         <id name="gradeid" type="integer">
12             <generator class="assigned">
13                 
14             </generator>
15         </id>
16         <property name="gradename" type="java.lang.String" />
17         <set name="stu" cascade="all">
18             <key column="gradeid"/>
19             <one-to-many class="Student"/>
20         </set>
21         
22     </class>
23 </hibernate-mapping>
24 
25 
26 <!--student表-->
27 <?xml version="1.0"?>
28 <!DOCTYPE hibernate-mapping PUBLIC 
29     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
30     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
31 
32 <hibernate-mapping
33     package="entity">
34     
35     <class name="Student" table="student" dynamic-update="true">
36         <id name="stuno" type="integer">
37             <generator class="sequence">
38                 <param name="sequence">seq_student</param>
39             </generator>
40         </id>
41         <property name="name" type="java.lang.String" />
42         
43         <!-- 多对一关系 -->
44         <many-to-one name="grade" class="Grade">
45             <column name="gradeid"></column>
46         </many-to-one>
47     </class>
48 </hibernate-mapping>

两表的配置文件

　　3.配置hibernate

 1 <!DOCTYPE hibernate-configuration PUBLIC
 2     "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 3     "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 4 
 5 <hibernate-configuration>
 6     <session-factory>
 7         
 8         <!-- 指定oracle对应得dialect -->
 9         <property name="dialect">
10             org.hibernate.dialect.Oracle10gDialect
11         </property>
12         <!-- 数据库jdbc驱动 -->
13         <property name="connection.driver_class">
14             oracle.jdbc.driver.OracleDriver
15         </property>
16         
17         <!-- 数据库url -->
18         <property name="connection.url">
19             jdbc:oracle:thin:@localhost:1521:XE
20         </property>
21         
22         <!-- 用户名 -->
23         <property name="connection.username">super_user</property>
24         <!-- 用户密码 -->
25         <property name="connection.password">abc123</property>
26         
27         <!-- session范围和上下文 -->
28         <property name="current_session_context_class">thread</property>
29         <!-- 是否在运行期间生成的SQL输出到日志以供调试 -->
30         <property name="show_sql">true</property>
31         <!-- 是否格式化sql -->
32         <property name="format_sql">true</property>
33         <!-- 根据映射文件自动生成表-->
34         <property name="hbm2ddl.auto">update</property> 
35         <!-- 映射 -->
36         <mapping resource="entity/Grade.hbm.xml" />
37         <mapping resource="entity/Student.hbm.xml" />
38         
39     </session-factory>
40 </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：

 1 package dao;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.Transaction;
 6 import org.hibernate.cfg.Configuration;
 7 
 8 import entity.Grade;
 9 import entity.Student;
10 
11 /**
12  * 多对一关系联动练习
13  * @author Administrator
14  *
15  */
16 public class StudentDao {
17     //打开配置
18     SessionFactory factory=new Configuration().configure().buildSessionFactory();
19     Session session=null;
20     
21     public static void main(String[] args) {
22         StudentDao stu=new StudentDao();
23         try {
24             //stu.update();
25             stu.del();
26         } catch (Exception e) {
27             // TODO Auto-generated catch block
28             e.printStackTrace();
29             
30         }
31     }
32     /**
33      * 新增
34      */
35     public void update() throws Exception{
36         session=factory.openSession();
37         session.beginTransaction();
38         //Grade grade=(Grade)session.get(Grade.class, 1);
39         
40         Student student=new Student();
41         Grade grade=new Grade();
42         grade.setGradeid(1);
43         grade.setGradename("一年级");
44         session.save(grade);
45         student.setName("小明");
46         student.setGrade(grade);
47         session.save(student);
48         session.getTransaction().commit();
49         System.out.println("成功！");
50         
51         session.close();
52     }
53     /**
54      * 删除
55      */
56     public void del(){
57         session=factory.openSession();
58         session.beginTransaction();
59         //Student student=(Student)session.get(Student.class, 5);
60         //级联删除
61         Grade grade=(Grade)session.get(Grade.class, 1);
62         session.delete(grade);
63         //session.delete(student);
64         session.getTransaction().commit();
65         System.out.println("成功！");
66         
67         session.close();
68     }
69 }

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