Hibernate！！多对多(单向|双向)关联映射

多对多——单向关联映射

 1 package com.hb.model;

 2 

 3 import java.util.HashSet;

 4 import java.util.Set;

 5 

 6 import javax.persistence.Entity;

 7 import javax.persistence.GeneratedValue;

 8 import javax.persistence.Id;

 9 import javax.persistence.ManyToMany;

10 import javax.persistence.Table;

11 

12 @Entity

13 @Table(name="t_teacher")

14 public class Teacher {

15     private  int  tid ;

16     private  String  tname;

17     private  Set<Student>  students = new  HashSet<Student>();

18     

19     @Id

20     @GeneratedValue

21     public int getTid() {

22         return tid;

23     }

24     public void setTid(int tid) {

25         this.tid = tid;

26     }

27     public String getTname() {

28         return tname;

29     }

30     public void setTname(String tname) {

31         this.tname = tname;

32     }

33     @ManyToMany

34     public Set<Student> getStudents() {

35         return students;

36     }

37     public void setStudents(Set<Student> students) {

38         this.students = students;

39     }

40     

41     

42 

43 }

package com.hb.model;



import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.Table;



@Entity

@Table(name="t_student")

public class Student {

    private  int sid; 

    private  String   sname;

    

    @Id

    @GeneratedValue

    public int getSid() {

        return sid;

    }

    public void setSid(int sid) {

        this.sid = sid;

    }

    public String getSname() {

        return sname;

    }

    public void setSname(String sname) {

        this.sname = sname;

    }

    

    



}

生成的表如下：

 

这样生成的中间表的名称是自动生成的，也可以通过加入一些属性改变表的名称

只需要在Teacher类里面添加一些属性，修改后的代码如下：

 1 @Entity

 2 @Table(name="t_teacher")

 3 public class Teacher {

 4     private  int  tid ;

 5     private  String  tname;

 6     private  Set<Student>  students = new  HashSet<Student>();

 7     

 8     @Id

 9     @GeneratedValue

10     public int getTid() {

11         return tid;

12     }

13     public void setTid(int tid) {

14         this.tid = tid;

15     }

16     public String getTname() {

17         return tname;

18     }

19     public void setTname(String tname) {

20         this.tname = tname;

21     }

22     @ManyToMany

23     @JoinTable(name="t_s",  //表名

24             joinColumns={ @JoinColumn(name="teacher_id")},  //  ？？？

25             inverseJoinColumns={@JoinColumn(name="student_id")}  // 对方那张表的对应的外键的id 

26         )

27     public Set<Student> getStudents() {

28         return students;

29     }

30     public void setStudents(Set<Student> students) {

31         this.students = students;

32     }

33 }

 

 

多对多单向关联在xml文件中的配置

 1 <hibernate-mapping>

 2     <class name="com.hb.model.Teacher">

 3         <id name="tid">

 4             <generator class="native"></generator>

 5         </id>

 6         

 7         <property name="tname"></property>

 8         <set name="students" table="t_s">

 9             <key column="teacher_id"></key>

10             <many-to-many class="com.hb.model.Student" column="student_id"/>

11         </set>

12     </class>

13     

14 </hibernate-mapping>

多对多——双向关联映射

• 很少用到
• 双向总会用到mappedBy