【hibernate框架】多对多双向关联(XML实现)-白红宇

多对多的双向关联：(非常少用)

通过老师可以知道他教了多少学生，这是单项多对多。而如果同时通过学生知道有多少个老师教他，那么就是多对多双向的关联。

XML实现：

Student.java:

package cn.edu.hpu.many2many;import java.util.HashSet; import java.util.Set;public class Student {	private int id;	private String name;		private Set
    
      teachers=new HashSet
     
      ();		public Set
      
        getTeachers() {		return teachers;	}	public void setTeachers(Set
       
         teachers) {		this.teachers = teachers;	}	public int getId() {		return id;	}	public void setId(int id) {		this.id = id;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}	}

Teacher.java:

package cn.edu.hpu.many2many;import java.util.HashSet;import java.util.Set;import cn.edu.hpu.many2many.Student;public class Teacher {	private int id;	private String name;	private Set
    
      students=new HashSet
     
      ();	//选择set的原因是因为，set互相之间不会有重复的	//跟数据库模型比较匹配	public int getId() {		return id;	}	public void setId(int id) {		this.id = id;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}		public Set
      
        getStudents() {		return students;	}	public void setStudents(Set
       
         students) {		this.students = students;	}	}

配置文件：

Student.hbm.xml:

Teacher.hbm.xml:

在hibernate.cfg.xml中配置：

生成的sql语句：

create table t_s (

student_id integer not null,

teacher_id integer not null,

primary key (teacher_id, student_id)

)

create table xm_student (

id integer not null auto_increment,

name varchar(255),

primary key (id)

)

create table xm_teacher (

id integer not null auto_increment,

name varchar(255),

primary key (id)

)

alter table t_s

add index FK1BF687B5893C2 (teacher_id),

add constraint FK1BF687B5893C2

foreign key (teacher_id)

references xm_teacher (id)

alter table t_s

add index FK1BF686ABD4922 (student_id),

add constraint FK1BF686ABD4922

foreign key (student_id)

references xm_student (id)

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