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多对一

比如说，我们很多个学生对应一个老师，这就是多对一。

CREATE TABLE `teacher` (  `id` INT(10) NOT NULL,  `name` VARCHAR(30) DEFAULT NULL,  PRIMARY KEY (`id`)) ENGINE=INNODB DEFAULT CHARSET=utf8INSERT INTO teacher(`id`, `name`) VALUES (1, '秦老师'); CREATE TABLE `student` (  `id` INT(10) NOT NULL,  `name` VARCHAR(30) DEFAULT NULL,  `tid` INT(10) DEFAULT NULL,  PRIMARY KEY (`id`),  KEY `fktid` (`tid`),  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)) ENGINE=INNODB DEFAULT CHARSET=utf8INSERT INTO `student` (`id`, `name`, `tid`) VALUES (1, '武少伟', 1); INSERT INTO `student` (`id`, `name`, `tid`) VALUES (2, '李鸿彬', 1); INSERT INTO `student` (`id`, `name`, `tid`) VALUES (3, '武少伟', 1); INSERT INTO `student` (`id`, `name`, `tid`) VALUES (4, '姚震', 1); INSERT INTO `student` (`id`, `name`, `tid`) VALUES (5, '夏彬峰', 1);

1. 首先建立实体类

package com.baidu.pojo;public class Student {
       private int id;    private String name;    private Teacher teacher;    public Student(int id, String name, Teacher teacher) {
           this.id = id;        this.name = name;        this.teacher = teacher;    }    public Student() {
       }    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 Teacher getTeacher() {
           return teacher;    }    public void setTeacher(Teacher teacher) {
           this.teacher = teacher;    }    @Override    public String toString() {
           return "Student{" +                "id=" + id +                ", name='" + name + '\'' +                ", teacher=" + teacher +                '}';    }}

package com.baidu.pojo;public class Teacher {
       private int id;    private String name;    public Teacher() {
       }    public Teacher(int id, String name) {
           this.id = id;        this.name = name;    }    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;    }    @Override    public String toString() {
           return "Teacher{" +                "id=" + id +                ", name='" + name + '\'' +                '}';    }}

2. 添加dao层代码

package com.baidu.dao;import com.baidu.pojo.Student;import java.util.List;public interface StudentDao {
       //获得全部学生的信息，以及对应的老师    List
   
     getStudents();    List
    
      getStudents2();}
    
   

3. 添加映射文件

   
   
        
            select * from mybatis.student        
            
         
        
            select * from mybatis.teacher where id = #{id}        
        
            select s.id,s.name,t.id as tid,t.name as tname from mybatis.student as s,mybatis.teacher as t        where s.tid = t.id        
            
             
             
             
                 
                  
              
         
    
   

4. 添加测试文件

package com.baidu.dao;import com.baidu.pojo.Student;import com.baidu.utils.MyBatisUtils;import org.apache.ibatis.session.SqlSession;import org.junit.Test;import java.util.List;public class StudentDaoTest {
       @Test    public void getStudents(){
           SqlSession sqlSession = MyBatisUtils.getSqlSession();        StudentDao mapper = sqlSession.getMapper(StudentDao.class);        List
   
     students = mapper.getStudents();        for (Student student : students) {
               System.out.println(student);        }    }    @Test    public void getStudents2(){
           SqlSession sqlSession = MyBatisUtils.getSqlSession();        StudentDao mapper = sqlSession.getMapper(StudentDao.class);        List
    
      students = mapper.getStudents2();        for (Student student : students) {
               System.out.println(student);        }    }}
    
   

一对多

1. 配置pojo层代码

package com.baidu.pojo;import java.util.List;public class Teacher {
       private int id;    private String name;    private List
   
     students;    public Teacher(int id, String name, List
    
      students) {
           this.id = id;        this.name = name;        this.students = students;    }    public Teacher() {
       }    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 List
     
       getStudents() {
           return students;    }    public void setStudents(List
      
        students) {
           this.students = students;    }    @Override    public String toString() {
           return "Teacher{" +                "id=" + id +                ", name='" + name + '\'' +                ", students=" + students +                '}';    }}
      
     
    
   

2. 配置dao层代码

Teacher getTeacher(int id);

3. 配置映射文件

   
       
            select s.id as sid,t.id as tid,s.name as sname,t.name as tname        from mybatis.student as s,mybatis.teacher as t        where s.tid = t.id and t.id = #{id}        
            
             
             
             
                 
                  
              
         
    
   

4. 测试

package com.baidu;import com.baidu.dao.TeacherDao;import com.baidu.pojo.Teacher;import com.baidu.utils.MyBatisUtils;import org.apache.ibatis.session.SqlSession;import org.junit.Test;public class TeacherDaoTest {
       @Test    public  void getTeacher(){
           SqlSession sqlSession = MyBatisUtils.getSqlSession();        TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);        Teacher teacher = mapper.getTeacher(1);        System.out.println(teacher);    }}

1. 配置dao层文件

Teacher getTeacherTwo(int id);

2. 配置映射文件

        select * from mybatis.teacher where id = #{id}        
           
        
               select * from mybatis.student where tid = #{id}    

3. 测试文件

@Test    public  void getTeacher2(){
           SqlSession sqlSession = MyBatisUtils.getSqlSession();        TeacherDao mapper = sqlSession.getMapper(TeacherDao.class);        Teacher teacher = mapper.getTeacherTwo(1);        System.out.println(teacher);    }

动态SQL查询

   
            delete from smbms.smbms_role        
                
     
                      id = #{id}            
             
        
       
   
            update smbms.smbms_role        
                
     
      roleCode = #{roleCode},
                 
     
      roleName = #{roleName},
                 
     
      createdBy = #{createdBy},
                 
     
      creationDate = #{creationDate},
                 
     
      modifyBy = #{modifyBy},
                 
     
      modifyDate = #{modifyDate},
             
        
   

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