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首先给大家推荐几个网页：

 没事看看 - MyBatis工具：www.mybatis.tk

 入门

  mybatis视频教程

 

一、多对多关系。

一般我们在设置多对多关系的时候，都是建立第三张关系表。

例子：学生t_student与课程t_courses，一个学生可以对应学习多门课程，一门课程对应可以有多名学生学习。第三张关系表t_stu_cou。

1）关系整理好，接着建立数据库表，添加信息。

1 create table t_student( 2  id int primary key auto_increment, 3  student_name varchar(20) 4 ); 5  6 create table t_courses( 7 id  int primary key auto_increment, 8 courses_name varchar(20) 9 );10 11 create table t_stu_cou(12  id int primary key auto_increment,13  fk_stu_id int,14  fk_cou_id int 15 );

 添加数据。

1 insert into t_student values (null,'米兰'); 2 insert into t_student values (null,'凌雪'); 3 insert into t_student values (null,'成成'); 4 insert into t_student values (null,'睿懿'); 5 insert into t_student values (null,'瑞瑞'); 6  7 insert into t_courses values (null,'语文'); 8 insert into t_courses values (null,'数学'); 9 insert into t_courses values (null,'计算机');10 insert into t_courses values (null,'java编程');11 insert into t_courses values (null,'html');12 13 insert into t_stu_cou values (null,1,1);14 insert into t_stu_cou values (null,1,2);15 insert into t_stu_cou values (null,2,3);16 insert into t_stu_cou values (null,2,4);17 insert into t_stu_cou values (null,3,1);18 insert into t_stu_cou values (null,3,5);19 insert into t_stu_cou values (null,4,4);20 insert into t_stu_cou values (null,4,2);

 

 

 2）建立JavaBean。

 CoursesBean.java

1 package com.cy.mybatis.beans; 2  3 import java.io.Serializable; 4 import java.util.List; 5 /** 6  * manyTOmany 7  * @author acer 8  * 9  */10 public class CoursesBean implements Serializable{11 12     13     private static final long serialVersionUID = 1L;14     private Integer id;15     private String name;16    // 使用 List
   
    集合，是说明学习这门课程的所有学生17     private List
    
      student;18     public CoursesBean() {19         super();20     }21     public CoursesBean(Integer id, String name, List
     
       student) {22         super();23         this.id = id;24         this.name = name;25         this.student = student;26     }27     public Integer getId() {28         return id;29     }30     public void setId(Integer id) {31         this.id = id;32     }33     public String getName() {34         return name;35     }36     public void setName(String name) {37         this.name = name;38     }39     public List
      
        getStudent() {40         return student;41     }42     public void setStudent(List
       
         student) {43         this.student = student;44     }45     @Override46     public String toString() {47         return "CoursesBean [id=" + id + ", name=" + name + ", student="48                 + student + "]";49     }50     51 52 }
       
      
     
    
   

 

 StudentBean.java

1 package com.cy.mybatis.beans; 2  3 import java.io.Serializable; 4 import java.util.List; 5 /** 6  * manyTOmany 7  * @author acer 8  * 9  */10 public class StudentBean implements Serializable{11 12     private static final long serialVersionUID = 1L;13      14     private Integer id;15     private String name;    16     private List
   
     courses;17     public StudentBean() {18         super();19         // TODO Auto-generated constructor stub20     }21     public StudentBean(Integer id, String name, List
    
      courses) {22         super();23         this.id = id;24         this.name = name;25         this.courses = courses;26     }27     public Integer getId() {28         return id;29     }30     public void setId(Integer id) {31         this.id = id;32     }33     public String getName() {34         return name;35     }36     public void setName(String name) {37         this.name = name;38     }39     public List
     
       getCourses() {40         return courses;41     }42     public void setCourses(List
      
        courses) {43         this.courses = courses;44     }45     @Override46     public String toString() {47         return "StudentBean [id=" + id + ", name=" + name + ", courses="48                 + courses + "]";49     }50     51 52 }
      
     
    
   

 

 

3) 定义接口  

CoursesMapper.java

1 package com.cy.mybatis.mapper; 2  3 import com.cy.mybatis.beans.CoursesBean; 4  5 public interface CoursesMapper { 6      7     /** 8      * 根据id查询课程 9      * @param id10      * @return11      */12     public CoursesBean findCouById(int id);13     14     /**15      * 要求查课时，将选课的学生一并查出16      * @param id17      * @return18      */19     public CoursesBean findCouAndStu(int id);20 21 22     23 24 }

 

StudentMapper.java

1 package com.cy.mybatis.mapper; 2  3 import com.cy.mybatis.beans.StudentBean; 4  5 public interface StudentMapper { 6     /** 7      * 根据id值查询学生信息 8      * @param id 9      * @return10      */11     public StudentBean findStuById(int id);12     13     /**14      * 要求查询学生时，将学生选择的课程查出15      * @param id16      * @return17      */18     public StudentBean findStuAndCou(int id);19 20 }

 

 

 4) 定义xml文件。CoursesMapper.xml    StudentMapper.xml

 mybatis实际是对XML进行操作，我们所有的方法都直接定义在XML中，写个接口只是为了更好的符合我们3层的思想.XML中只要有方法，就可以使用，而调用的方式就是：namespace+方法名；

 CoursesMapper.xml 

 

1 
    2  3 
   
     4  5  6  
    
      7    
        9                            10     
     11     
     12  
    13 14  
    
     15     
     16     
     17     18     
     20     
     21  
    22 23 24     25  
    26   select * from t_courses where id=#{id}27  28  29  30  31  
    33  
    34     select * from t_student where id in (select fk_stu_id from t_stu_cou where fk_cou_id=#{id})35  36     37  
    38  select * from t_courses where id=#{id}39  40 
   

 

 StudentMapper.xml

1 
    2  3 
   
     4  5 
    
      6     
      7     
      8 
     9 10 
    
     11      
     12      
     13      
     14 
    15     
    16         select * from t_student where id = #{id}17     18     19     
    20         select * from t_student where id = #{id}21     22     
    23         select * from t_courses where id in (select fk_cou_id from t_stu_cou where fk_stu_id = #{id})24     25     26 
   

 

 5) 测试

1 package com.cy.mybatis.service; 2  3 import org.apache.ibatis.session.SqlSession; 4  5 import com.cy.mybatis.beans.CoursesBean; 6 import com.cy.mybatis.beans.StudentBean; 7 import com.cy.mybatis.mapper.CoursesMapper; 8 import com.cy.mybatis.mapper.StudentMapper; 9 import com.cy.mybatis.tools.DBTools;10 11 12 13 public class ManyToManyService {14     15     public static void main(String[] args) {16         17         findStudentByCourses();18         findCoursesByStudent();19     }20 21     22 23     private static void findCoursesByStudent() {24         SqlSession session = DBTools.getSession();25         StudentMapper sm=session.getMapper(StudentMapper.class);26         StudentBean sb=sm.findStuAndCou(1);27         System.out.println(sb);28         29     }30 31 32 33     private static void findStudentByCourses() {34         SqlSession session = DBTools.getSession();35         CoursesMapper cm=session.getMapper(CoursesMapper.class);36         CoursesBean cb=cm.findCouAndStu(2);37         System.out.println(cb);38     }39 40 }

 

 结果显示：

1 DEBUG 2016-02-27 09:56:53,852 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection 2 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 586269. 3 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@8f21d] 4 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select * from t_courses where id=?  5 DEBUG 2016-02-27 09:56:54,105 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 2(Integer) 6 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====>  Preparing: select * from t_student where id in (select fk_stu_id from t_stu_cou where fk_cou_id=?)  7 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====> Parameters: 2(Integer) 8 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <====      Total: 2 9 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 110 CoursesBean [id=2, name=数学, student=[StudentBean [id=1, name=米兰, courses=null], StudentBean [id=4, name=睿懿, courses=null]]]11 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection12 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 23881129.13 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@16c65a9]14 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select * from t_student where id = ? 15 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 1(Integer)16 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====>  Preparing: select * from t_courses where id in (select fk_cou_id from t_stu_cou where fk_stu_id = ?) 17 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====> Parameters: 1(Integer)18 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <====      Total: 219 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 120 StudentBean [id=1, name=米兰, courses=[CoursesBean [id=1, name=语文, student=null], CoursesBean [id=2, name=数学, student=null]]]

 

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