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1 多对一处理

多个学生关联一个老师

1.1 环境配置

pom.xml

   
       
            
     
      myBatis
             
     
      org.example
             
     
      1.0-SNAPSHOT
         
        
    
     4.0.0
        
    
     myBatis_01
        
            
     
      8
             
     
      8
         
       
        
            
                 
                      
       
        src/main/java
                       
                           
        
         **/*.xml
                            
        
         **/*.properties
                        
                   
                  
                      
       
        src/main/resources
                       
                           
        
         **/*.xml
                            
        
         **/*.properties
                        
                   
              
         
        
            
             
                 
      
       log4j
                  
      
       log4j
                  
      
       1.2.17
              
             
                 
      
       org.projectlombok
                  
      
       lombok
                  
      
       1.16.10
              
         
    
   

核心配置文件mybatis-config.xml

数据库

/* Navicat Premium Data Transfer Source Server         : localhost Source Server Type    : MySQL Source Server Version : 50527 Source Host           : localhost:3306 Source Schema         : mybatis Target Server Type    : MySQL Target Server Version : 50527 File Encoding         : 65001 Date: 20/01/2021 12:12:55*/SET NAMES utf8mb4;SET FOREIGN_KEY_CHECKS = 0;-- ------------------------------ Table structure for student-- ----------------------------DROP TABLE IF EXISTS `student`;CREATE TABLE `student`  (  `id` int(11) NOT NULL,  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,  `tid` int(11) DEFAULT NULL,  PRIMARY KEY (`id`) USING BTREE,  INDEX `tid`(`tid`) USING BTREE,  CONSTRAINT `tid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;SET FOREIGN_KEY_CHECKS = 1;

/* Navicat Premium Data Transfer Source Server         : localhost Source Server Type    : MySQL Source Server Version : 50527 Source Host           : localhost:3306 Source Schema         : mybatis Target Server Type    : MySQL Target Server Version : 50527 File Encoding         : 65001 Date: 20/01/2021 12:25:12*/SET NAMES utf8mb4;SET FOREIGN_KEY_CHECKS = 0;-- ------------------------------ Table structure for teacher-- ----------------------------DROP TABLE IF EXISTS `teacher`;CREATE TABLE `teacher`  (  `id` int(11) NOT NULL,  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,  PRIMARY KEY (`id`) USING BTREE) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;-- ------------------------------ Records of teacher-- ----------------------------INSERT INTO `teacher` VALUES (1, 'teacher_zs');SET FOREIGN_KEY_CHECKS = 1;

实体类的构建

@Datapublic class Student {       private int id;    private String name;   //多个学生可以是同一个老师，即多对一    private Teacher teacher;}

@Datapublic class Teacher {       private int id;    private String name;}

接口的构建

public interface TeacherMapper {       @Select("select * from teacher where id = #{id}")    Teacher getTeacherById(@Param("id") int id);}

测试类的编写

public class DaoTest {       //注意导包：org.apache.log4j.Logger    static Logger logger = Logger.getLogger(DaoTest.class);    @Test    public  void test(){          try(SqlSession sqlSession = MyBatisUtils.getSqlSesion();){              TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);           Teacher teacher = mapper.getTeacherById(1);           System.out.println(teacher);       }    }}

测试成功！！！

1.2 按查询嵌套处理

StudentMapper.xml

   
   
   
   
       
            select * from student        
        	
             
         
            
            select * from teacher where id = #{   id}    
   

测试类

@Test    public void getStudent() {           try(SqlSession sqlSession = MyBatisUtils.getSqlSesion();){               StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);            List
   
     studentList = mapper.getStudents();            System.out.println(studentList);        }    }
   

1.3 按结果嵌套处理

   
   
   
   
       
            SELECT s.id sid , s.name sname , t.name tname        FROM student s , teacher t        WHERE s.tid = t.id        
            
             
             
                 
              
         
    
   

2 一对多处理

2.1 按结果嵌套处理

实体类的编写

@Datapublic class Student {      private int id;   private String name;   private int tid;}

@Data public class Teacher {      private int id;   private String name;   //一个老师多个学生   private List
   
     students;}
   

TeacherMapper接口编写方法

public interface TeacherMapper {       Teacher getTeacher(@Param("id") int id);}

编写接口对应的Mapper配置文件

   
       
            SELECT s.id sid, s.name sname , t.name tname, t.id tid        FROM student s,teacher t        WHERE s.tid = t.id and t.id=#{   id}        
            
             
                 
                  
              
         
    
   

测试类

public class DaoTest {       //注意导包：org.apache.log4j.Logger    static Logger logger = Logger.getLogger(DaoTest.class);    @Test    public  void test(){          try(SqlSession sqlSession = MyBatisUtils.getSqlSesion();){              TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);           Teacher teacher = mapper.getTeacher(1);           System.out.println(teacher);       }    }}

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