Hibernate关系映射之many-to-many(多对多)


在表设计中，我们一般都会考虑表与表之间的关系，现在我来介绍一下表与表之间的几种对应关系
many-to-many 多对多 比如一个用户可以有多种角色 一种角色可以对用多个不同的用户
所以角色和用户之间的关系是多对多的关系 一般要用第三张表表示两者对应的关系
one-to-many 一对多  比如一个老师可以对应很多个学生
many-to-one 相反的是多对一  
one-to-one  一对一 比如公民和身份证就是一一对应的

Demo实验：学生与课程之间的关系

1.创建StuCourse类和StuCourse.hbm.xml 表示Student与Course之间的对应关系
 1 package com.ansibee.domain;
 2 
 3 public class StuCourse {
 4     private Integer id;
 5     private Student student;
 6     private Course course;
 7     private Integer grade;
 8     public Integer getId() {
 9         return id;
10     }
11     public void setId(Integer id) {
12         this.id = id;
13     }
14     public Student getStudent() {
15         return student;
16     }
17     public void setStudent(Student student) {
18         this.student = student;
19     }
20     public Course getCourse() {
21         return course;
22     }
23     public void setCourse(Course course) {
24         this.course = course;
25     }
26     public Integer getGrade() {
27         return grade;
28     }
29     public void setGrade(Integer grade) {
30         this.grade = grade;
31     }
32 }

<!--StuCourse.hbm.xml-->

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <hibernate-mapping package="com.ansibee.domain">
 5 <class name="StuCourse" >
 6 <id name="id" type="java.lang.Integer">
 7 <generator class="increment">
 8 <param name="increment">stucourse_inc</param>
 9 </generator>
10 </id>
11 <property name="grade" type="java.lang.Integer">
12 <column name="grade" length="3"/>
13 </property>
14 <many-to-one name="course" column="course_id"/>
15 <many-to-one name="student" column="student_id"/>
16 </class>
17 </hibernate-mapping>


2.创建Student类和Student.hbm.xml文件
 1 package com.ansibee.domain;
 2 
 3 import java.util.Set;
 4 
 5 public class Student {
 6     private Integer id;
 7     private String name;
 8     private Set<StuCourse> stuCourses;
 9     public Integer getId() {
10         return id;
11     }
12     public void setId(Integer id) {
13         this.id = id;
14     }
15     public String getName() {
16         return name;
17     }
18     public void setName(String name) {
19         this.name = name;
20     }
21     public Set<StuCourse> getStuCourses() {
22         return stuCourses;
23     }
24     public void setStuCourses(Set<StuCourse> stuCourses) {
25         this.stuCourses = stuCourses;
26     }
27 }

<!--Student.hbm.xml-->

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <hibernate-mapping package="com.ansibee.domain">
 5 <class name="Student">
 6 <id name="id" type="java.lang.Integer">
 7 <generator class="increment">
 8 <param name="increment">stu_inc</param>
 9 </generator>
10 </id>
11 <property name="name" type="java.lang.String">
12 <column name="name" length="64"/>
13 </property>
14 <!-- 这里我们配置了one-to-many 一个学生可以对应多个选课记录 -->
15 <set name="stuCourses">
16 <key column="student_id"/>
17 <one-to-many class="StuCourse"/>
18 </set>
19 </class>
20 </hibernate-mapping>

　3.创建Course类和Course.hbm.xml文件

 1 package com.ansibee.domain;
 2 
 3 import java.util.Set;
 4 
 5 public class Course {
 6     private Integer id;
 7     private String name;
 8     private Set<StuCourse> stuCourses;
 9     public Integer getId() {
10         return id;
11     }
12     public void setId(Integer id) {
13         this.id = id;
14     }
15     public String getName() {
16         return name;
17     }
18     public void setName(String name) {
19         this.name = name;
20     }
21     public Set<StuCourse> getStuCourses() {
22         return stuCourses;
23     }
24     public void setStuCourses(Set<StuCourse> stuCourses) {
25         this.stuCourses = stuCourses;
26     }
27 }

<!--Course.hbm.xml-->

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <hibernate-mapping package="com.ansibee.domain">
 5 <class name="Course">
 6 <id name="id" type="java.lang.Integer">
 7 <generator class="increment">
 8 <param name="increment">course_inc</param>
 9 </generator>
10 </id>
11 <property name="name" type="java.lang.String">
12 <column name="name" length="64"/>
13 </property>
14 <!-- 配置one-to-many 表示一门课程可以对应多个选课记录 -->
15 <set name="stuCourses">
16 <key column="course_id"/>
17 <one-to-many class="StuCourse"/>
18 </set>
19 </class>
20 </hibernate-mapping>

4.完成以上步骤就可以创建Hibernate工具类完成CRUD操作

  1 package com.ansibee.util;
  2 import java.util.List;
  3 
  4 import org.hibernate.Query;
  5 import org.hibernate.Session;
  6 import org.hibernate.SessionFactory;
  7 import org.hibernate.Transaction;
  8 import org.hibernate.cfg.Configuration;
  9 
 10 final public class HibernateUtil {
 11     private static SessionFactory sessionFactory=null;
 12     //使用线程局部模式
 13     private static ThreadLocal<Session> threadLocal=new ThreadLocal<Session>();
 14     private HibernateUtil(){};
 15     static {
 16         sessionFactory=new Configuration().configure().buildSessionFactory();
 17     }
 18     
 19     //关闭sessionFactory
 20     public static void closeSessionFactory(){
 21         sessionFactory.close();
 22     }
 23     
 24     //获取全新的全新的session
 25     public static Session openSession(){
 26         return sessionFactory.openSession();
 27     }
 28     //获取和线程关联的session
 29     public static Session getCurrentSession(){
 30         
 31         Session session=threadLocal.get();
 32         //判断是否得到
 33         if(session==null){
 34             session=sessionFactory.openSession();
 35             //把session对象设置到 threadLocal,相当于该session已经和线程绑定
 36             threadLocal.set(session);
 37         }
 38         return session;
 39                 
 40     }
 41     
 42     //提供一个统一的查询方法 hql形式 from类 where 条件=？..
 43     public static List executeQuery(String hql,String[] parameters){
 44         
 45         Session session = null;
 46         List list = null;
 47         
 48         try {
 49             session = openSession();
 50             Query query = session.createQuery(hql);
 51             //先判断是否有参数绑定
 52             if(parameters!=null&&parameters.length>0){
 53                 for(int i=0;i<parameters.length;i++){
 54                     query.setString(i, parameters[i]);
 55                 }
 56             }
 57             list = query.list();
 58         } catch (Exception e) {
 59             e.printStackTrace();
 60             throw new RuntimeException(e.getMessage());
 61         }finally{
 62             if(session!=null&&session.isOpen()){
 63                 session.close();
 64             }
 65         }
 66         return list;
 67     }
 68     
 69     //提供一个统一的查询方法(带分页)hql形式 from 类  where 条件=？..
 70     public static List executeQueryByPage(String hql,String[] parameters,int pageSize,int pageNow){
 71         
 72         Session session = null;
 73         List list = null;
 74         
 75         try {
 76             session = openSession();
 77             Query query = session.createQuery(hql);
 78             //先判断是否有参数绑定
 79             if(parameters!=null&&parameters.length>0){
 80                 for(int i=0;i<parameters.length;i++){
 81                     query.setString(i, parameters[i]);
 82                 }
 83             }
 84             
 85             //分页
 86             query.setFirstResult((pageNow-1)*pageSize).setMaxResults(pageSize);
 87             
 88             list = query.list();
 89         } catch (Exception e) {
 90             e.printStackTrace();
 91             throw new RuntimeException(e.getMessage());
 92         }finally{
 93             if(session!=null&&session.isOpen()){
 94                 session.close();
 95             }
 96         }
 97         return list;
 98     }
 99     
100     //统一的添加方法
101     public static void save(Object obj){
102         Session session=null;
103         Transaction ts=null;
104         
105         try {
106             session=openSession();
107             ts=session.beginTransaction();
108             session.save(obj);
109             ts.commit();
110         } catch (Exception e) {
111             if(ts!=null){
112                 ts.rollback();
113             }
114             throw new RuntimeException(e.getMessage());
115         }finally{
116             if(session!=null&&session.isOpen()){
117                 session.close();
118             }
119         }
120     }
121     
122     //统一提供一个修改和删除（批量hql）hql"delete update ...??"
123     public static void executeUpdate(String hql,String[] parameters){
124         
125         Session session=null;
126         Transaction ts =null;
127         try {
128             session=openSession();
129             ts=session.beginTransaction();
130             Query query=session.createQuery(hql);
131             //先判断是否有参数要绑定
132             if(parameters!=null&&parameters.length>0){
133                 for(int i=0;i<parameters.length;i++){
134                     query.setString(i, parameters[i]);
135                 }
136             }
137             query.executeUpdate();
138             ts.commit();
139         } catch (Exception e) {
140             e.printStackTrace();
141             throw new RuntimeException(e.getMessage());
142         }finally{
143             if(session!=null&&session.isOpen()){
144                 session.close();
145             }
146         }
147     }
148 }

5.配置hibernate.cfg.xml

 1 <?xml version='1.0' encoding='UTF-8'?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3           "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4           "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 5 <!-- Generated by MyEclipse Hibernate Tools.                   -->
 6 <hibernate-configuration>
 7 
 8     <session-factory>
 9         <property name="myeclipse.connection.profile">com.mysql.jdbc.Driver</property>
10         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
11         <property name="connection.password">123</property>
12         <property name="connection.username">root</property>
13         <property name="connection.url">jdbc:mysql://localhost:3306/employee</property>
14         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
15         <property name="show_sql">true</property>
16         <!-- 配置让hibernate自动创建关系模型(表) -->
17         <property name="format_sql">false</property>
18         <property name="hbm2ddl.auto">update</property>
19         <mapping resource="com/ansibee/domain/Course.hbm.xml" />
20         <mapping resource="com/ansibee/domain/StuCourse.hbm.xml" />
21     <mapping resource="com/ansibee/domain/Student.hbm.xml" />
22     </session-factory>
23 
24 </hibernate-configuration>

6.编写测试类TestMain

 1 package com.ansibee.view;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.Transaction;
 5 
 6 import com.ansibee.domain.Course;
 7 import com.ansibee.domain.StuCourse;
 8 import com.ansibee.domain.Student;
 9 import com.ansibee.util.HibernateUtil;
10 
11 public class TestMain {
12 
13     public static void main(String[] args) {
14 
15         Session session = null;
16         Transaction ts = null;
17 
18         try {
19             // 使用基础模板
20             session = HibernateUtil.getCurrentSession();
21             ts = session.beginTransaction();
22 
23             //添加一个学生，一门课程，选课
24             Student stu1 = new Student();
25             stu1.setName("小共");
26             
27             Course course = new Course();
28             course.setName("C#");
29             
30             StuCourse sc = new StuCourse();
31             sc.setGrade(95);
32             sc.setCourse(course);
33             sc.setStudent(stu1);
34             
35             //顺序保存
36             session.save(stu1);
37             session.save(course);
38             session.save(sc);
39             
40             ts.commit();
41         } catch (Exception e) {
42             if (ts != null) {
43                 ts.rollback();
44             }
45             e.printStackTrace();
46 
47             // TODO: handle exception
48         } finally {
49             if (session != null && session.isOpen()) {
50                 session.close();
51             }
52         }
53     }
54 
55 }

7.测试运行

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原文地址：https://www.cnblogs.com/ansibee/p/7073611.html