Hibernate 一对多双向关联Demo

以Classes[班级]和Student[学生]为例的Demo

//Classes.java
public class Classes implements Serializable {
    private long cid;
    private String cname;
    private String cdesc;
    private Set<Student> students;
     //get和set
    
}

//Student .java

public class Student implements Serializable {
    private long sid;
    private String sname;
    private String sdesc;
    private Classes classes;
    
    //get和set
}

 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>
 5     <class name="cn.test.testDoubl.Classes" >
 6         <id name="cid" type="java.lang.Long" length="5">
 7             <column name="cid"></column>
 8             <generator class="increment"></generator>
 9         </id>
10         <property name="cname" type="java.lang.String" length="20"></property>
11         <property name="cdesc" type="java.lang.String" length="50"></property>
12         <!-- 
13             cascade指的是对象对对象的操作
14             inverse指的是对象对关系的操作
15          -->
16         <set name="students" cascade="all">
17             <key>
18             <!-- 
19                     通过classes建立与student之间的联系
20                  -->
21                 <column name="cid"></column>
22             </key>
23             <one-to-many class="cn.test.testDoubl.Student"/>
24         </set>
25     </class>
26 </hibernate-mapping>

 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>
 5     <class name="cn.test.testDoubl.Student">
 6         <id name="sid" type="java.lang.Long" length="5">
 7             <column name="sid"></column>
 8             <generator class="increment"></generator>
 9         </id>
10         <property name="sname" type="java.lang.String" length="20"></property>
11         <property name="sdesc" type="java.lang.String" length="50"></property>
12         <!-- 
13             多对一
14                注意：在many-to-one中没有inverse属性
15                      对student表的修改本身就是维护外键
16          -->
17         <many-to-one name="classes" class="cn.test.testDoubl.Classes" cascade="all">
18         <!-- 
19                 外键
20                    描述了通过student建立与classes之间的联系
21              -->
22             <column name="cid"></column>
23         </many-to-one>
24     </class>
25 </hibernate-mapping>

总结：

当发生transaction.commit的时候，hibernate内部会检查所有的持久化对象会对持久化对象做一个更新,因为classes是一个持久化状态的对象，所以hibernate 内部要对classes进行更新，因为在classes.hbm.xml文件中<set name="students" cascade="all" inverse="true"> 意味着在更新classes的时候，要级联操作student,而student是一个临时状态的对象所以要对student进行保存，在保存student的时候，就把外键更新了。

  1 package cn.test.testDoubl;
  2 
  3 import java.util.HashSet;
  4 import java.util.Set;
  5 
  6 import org.hibernate.Session;
  7 import org.hibernate.SessionFactory;
  8 import org.hibernate.Transaction;
  9 import org.hibernate.cfg.Configuration;
 10 import org.junit.Test;
 11 
 12 public class DoTestDoubl {
 13     private static SessionFactory sessionFactory;
 14     static{
 15         Configuration configuration=new Configuration();
 16         configuration.configure("cn/test/testDoubl/hibernate.cfg.xml");
 17         sessionFactory=configuration.buildSessionFactory();
 18     }
 19     
 20     /**
 21      * 1、保存班级
 22      * 2、保存学生
 23      * 3、保存班级的时候同时保存学生
 24      * 4、保存班级的时候同时保存学生，并且建立班级和学生之间的关系
 25      * 5、已经存在一个班级，新建一个学生，并且建立该学生和该班级之间的关系
 26      * 6、已经存在一个学生，新建一个班级，并且建立该学生和该班级之间的关系
 27      * 7、已经存在一个学生，已经存在一个班级，解除该学生和原来班级之间的关系，建立该学生和新班级之间的关系
 28      * 8、已经存在一个学生，解除该学生和该学生所在班级之间的关系
 29      * 9、解除该班级和所有的学生之间的关系，再重新建立该班级和一些新的学员之间的关系
 30      * 10、解除该班级和所有的学生之间的关系
 31      * 11、删除班级
 32      *      *
 33      *          *  解除该班级和所有的学生之间的关系
 34      *          *  删除该班级
 35      *      *   
 36      *          删除班级的同时删除学生
 37      * 12、删除学生
 38      *      同删除班级
 39      */
 40     
 41     //3、保存班级的时候同时保存学生
 42     /*
 43      *  Hibernate: select max(cid) from Classes
 44         Hibernate: select max(sid) from Student
 45         Hibernate: insert into Classes (cname, cdesc, cid) values (?, ?, ?)
 46         Hibernate: insert into Student (sname, sdesc, cid, sid) values (?, ?, ?, ?)
 47         Hibernate: update Student set cid=? where sid=?
 48      */
 49     
 50     @Test
 51     public void testSaveClassesandStudent(){
 52         
 53         Session session=sessionFactory.openSession();
 54         Transaction transaction=session.beginTransaction();
 55         Student student=new Student();
 56         student.setSname("1111");
 57         student.setSdesc("111111111111");
 58         
 59         Set<Student> set=new HashSet<Student>();
 60         set.add(student);
 61         
 62         Classes classes=new Classes();
 63         classes.setCname("oo1");
 64         classes.setCdesc("我们都是No。1");
 65         
 66         classes.setStudents(set);
 67         
 68         session.save(classes);
 69         
 70         transaction.commit();
 71         session.close();
 72         
 73     }
 74     
 75     
 76     //4、保存班级的时候同时保存学生，并且建立班级和学生之间的关系
 77     /*
 78      *  Hibernate: select max(sid) from Student
 79         Hibernate: select max(cid) from Classes
 80         Hibernate: insert into Classes (cname, cdesc, cid) values (?, ?, ?)
 81         Hibernate: insert into Student (sname, sdesc, cid, sid) values (?, ?, ?, ?)
 82      */
 83     @Test
 84     public void testSaveClassesandStudent2(){
 85         
 86         Session session=sessionFactory.openSession();
 87         Transaction transaction=session.beginTransaction();
 88         
 89         Student student=new Student();
 90         student.setSname("1111");
 91         student.setSdesc("111111111111");
 92                 
 93         Classes classes=new Classes();
 94         classes.setCname("oo1");
 95         classes.setCdesc("我们都是No。1");    
 96         
 97         student.setClasses(classes);//通过student来维护classes
 98                                     //对student的增、删、改本身就是对外键的操作，所以这里不再发出update语句
 99                                      //一对多，多的一方维护关系，效率比较高
100         
101         session.save(student);
102         
103         transaction.commit();
104         session.close();
105         
106     }
107     
108     //5、已经存在一个班级，新建一个学生，并且建立该学生和该班级之间的关系
109     /*
110      *  Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_, classes0_.cdesc as cdesc0_0_ from Classes classes0_ where classes0_.cid=?
111         Hibernate: select max(sid) from Student
112         Hibernate: insert into Student (sname, sdesc, cid, sid) values (?, ?, ?, ?)
113      */
114     @Test
115     public void testSaveStudentToClasses(){
116         Session session =sessionFactory.openSession();
117         Transaction transaction=session.beginTransaction();
118         
119         Classes classes=(Classes) session.get(Classes.class, 1L);
120         
121         Student student=new Student();
122         student.setSname("王尼玛");
123         student.setSdesc("暴走漫画，就是劲爆");
124         student.setClasses(classes);
125         
126         session.save(student);
127         
128         transaction.commit();
129         session.close();
130     }
131     
132     //6、已经存在一个学生，新建一个班级，并且建立该学生和该班级之间的关系
133     /*
134      *  Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_, student0_.sdesc as sdesc1_0_, student0_.cid as cid1_0_ from Student student0_ where student0_.sid=?
135         Hibernate: select max(cid) from Classes
136         Hibernate: insert into Classes (cname, cdesc, cid) values (?, ?, ?)
137         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
138      */
139     @Test
140     public void testSaveClassesToStudent(){
141         Session session=sessionFactory.openSession();
142         Transaction transaction=session.beginTransaction();
143         
144         Student student=(Student) session.get(Student.class, 1L);
145         
146         Classes classes=new Classes();
147         classes.setCname("黑客集训");
148         classes.setCdesc("里面都是牛人");
149         
150         student.setClasses(classes);
151         
152         session.save(classes);
153         
154         transaction.commit();
155         session.close();
156     }
157     
158     //7、已经存在一个学生，已经存在一个班级，解除该学生和原来班级之间的关系，建立该学生和新班级之间的关系
159     /*
160      *  Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_, classes0_.cdesc as cdesc0_0_ from Classes classes0_ where classes0_.cid=?
161         Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_, student0_.sdesc as sdesc1_0_, student0_.cid as cid1_0_ from Student student0_ where student0_.sid=?
162         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
163      */
164     @Test
165     public void testToRebuild(){
166         Session session=sessionFactory.openSession();
167         Transaction transaction=session.beginTransaction();
168         
169         Classes classes=(Classes) session.get(Classes.class, 1L);
170         Student student=(Student) session.get(Student.class, 1L);
171         student.setClasses(classes);
172         transaction.commit();
173         session.close();
174     }
175     
176     //8、已经存在一个学生，解除该学生和该学生所在班级之间的关系
177     /*
178      *  Hibernate: select student0_.sid as sid1_0_, student0_.sname as sname1_0_, student0_.sdesc as sdesc1_0_, student0_.cid as cid1_0_ from Student student0_ where student0_.sid=?
179         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
180      */
181     @Test
182     public void testToRomove(){
183         Session session=sessionFactory.openSession();
184         Transaction transaction=session.beginTransaction();
185         
186         Student student=(Student) session.get(Student.class, 1L);
187         student.setClasses(null);
188         
189         transaction.commit();
190         session.close();
191     }
192     
193     //9、解除该班级和所有的学生之间的关系，再重新建立该班级和一些新的学员之间的关系
194     /*
195      *  Hibernate: select classes0_.cid as cid0_0_, classes0_.cname as cname0_0_, classes0_.cdesc as cdesc0_0_ from Classes classes0_ where classes0_.cid=?
196         Hibernate: select students0_.cid as cid0_1_, students0_.sid as sid1_, students0_.sid as sid1_0_, students0_.sname as sname1_0_, students0_.sdesc as sdesc1_0_, students0_.cid as cid1_0_ from Student students0_ where students0_.cid=?
197         Hibernate: select max(sid) from Student
198         Hibernate: insert into Student (sname, sdesc, cid, sid) values (?, ?, ?, ?)
199         Hibernate: insert into Student (sname, sdesc, cid, sid) values (?, ?, ?, ?)
200         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
201         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
202         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
203         Hibernate: update Student set sname=?, sdesc=?, cid=? where sid=?
204         Hibernate: update Student set cid=? where sid=?
205         Hibernate: update Student set cid=? where sid=?
206      */
207     @Test
208     public void testremoveAndRebuild(){
209         Session session=sessionFactory.openSession();
210         Transaction transaction=session.beginTransaction();
211         
212         Classes classes=(Classes) session.get(Classes.class, 2L);
213         Set<Student> students=classes.getStudents();
214         for(Student student:students)
215         {
216             student.setClasses(null);
217         }
218         
219         Student student=new Student();
220         student.setSname("新建1");
221         student.setSdesc("新建轩辕rtyuio");
222         Student student2=new Student();
223         student2.setSname("新建2");
224         student2.setSdesc("新建轩sdfghyujikol;辕rtyuio");
225         
226         students.add(student);
227         students.add(student2);
228         
229         transaction.commit();
230         session.close();
231     }
232     
233     //10、解除该班级和所有的学生之间的关系
234     @Test
235     public void testRemoveAllStudents(){
236         Session session=sessionFactory.openSession();
237         Transaction transaction=session.beginTransaction();
238         
239         Classes classes=(Classes) session.get(Classes.class, 2L);
240         Set<Student> students= classes.getStudents();
241         for(Student student:students){
242             student.setClasses(null);
243         }
244         transaction.commit();
245         session.close();
246     }
247     
248     //11、删除班级
249     //先解除关系，再删除班级
250     @Test
251     public void testDeleteClasses(){
252         Session session=sessionFactory.openSession();
253         Transaction transaction=session.beginTransaction();
254         
255         Classes classes=(Classes) session.get(Classes.class, 1L);
256         Set<Student> set=classes.getStudents();
257         for(Student student:set){
258             student.setClasses(null);
259         }
260         session.delete(classes);
261         transaction.commit();
262         session.close();
263     }
264     
265     //在删除班级的时候，同时删除整个班级的学生
266     
267     @Test
268     public void testDeleteClasses2(){
269         Session session=sessionFactory.openSession();
270         Transaction transaction=session.beginTransaction();
271         
272         Classes classes=(Classes) session.get(Classes.class, 2L);
273         Set<Student> set=classes.getStudents();
274         for(Student student:set){
275             student.setClasses(null);
276             break;
277         }
278         //session.delete(classes);
279         transaction.commit();
280         session.close();
281     }
282     
283 }

一对多双向关联例子

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原文地址：https://www.cnblogs.com/liuwt365/p/4220052.html