"查"操作(企业开发中尽量不使用*,需要哪些字段就写哪些字段,都需要就全写上)

Mybatis 会自动地根据数据库的字段名和Java对象的属性名进行映射,如果名称一样就进行赋值

但是那些名称不一样的,我们想要拿到,该怎么拿呢?

一开始数据库字段名和Java对象属性名如下图所示,名称不一样

 

解决办法:

1.对 Mysql 的查询结果进行重命名 ,在@Select括号里面把这三个字段名用as修改成Java对象属性名

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import org.apache.ibatis.annotations.*;

import java.util.List;

@Mapper
public interface UserInfoMapper {
    @Select("select id, username, password, age, gender, phone, delete_flag as deleteflag, create_time as createtime, update_time as updatetime" +
            " from userInfo")
    List<UserInfo> selectAll();

}

右键,generate,test,勾选,OK

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.List;

import static org.junit.jupiter.api.Assertions.*;

@Slf4j
@SpringBootTest
class UserInfoMapperTest {
    @Autowired
    private UserInfoMapper userInfoMapper;
    @Test
    void selectAll() {
        List<UserInfo> list = userInfoMapper.selectAll();
        log.info(list.toString());
    }

}

每列数据就都能找到了 

2.使用 @Result 注解

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import org.apache.ibatis.annotations.*;

import java.util.List;

@Mapper
public interface UserInfoMapper {
    
    @Results({
            @Result(column = "delete_flag",property = "deleteFlag"),
            @Result(column = "create_time",property = "createTime"),
            @Result(column = "update_time",property = "updateTime")
    })
    @Select("select * from userInfo")
    List<UserInfo> selectAll2();

    
}

右键,generate,test,勾选,OK

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.List;

import static org.junit.jupiter.api.Assertions.*;

@Slf4j
@SpringBootTest
class UserInfoMapperTest {
    @Autowired
    private UserInfoMapper userInfoMapper;
    
    @Test
    void selectAll2() {
        List<UserInfo> list = userInfoMapper.selectAll();
        log.info(list.toString());
    }
}

成功

当我们别的时候也需要查找 delete_flag 和 create_time 和 update_time,就也需要写这一段语句

@Results({
        @Result(column = "delete_flag",property = "deleteFlag"),
        @Result(column = "create_time",property = "createTime"),
        @Result(column = "update_time",property = "updateTime")
})

这样就太繁琐了

接下来我们学习如何复用 Result 的定义,加上 id 和 value

然后哪里需要用就在前面加上@ResultMap

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import org.apache.ibatis.annotations.*;

import java.util.List;

@Mapper
public interface UserInfoMapper {
   

    @Results(id="BaseMap",value = {
            @Result(column = "delete_flag",property = "deleteFlag"),
            @Result(column = "create_time",property = "createTime"),
            @Result(column = "update_time",property = "updateTime")
    })
    @Select("select * from userInfo")
    List<UserInfo> selectAll2();

    @ResultMap(value = "BaseMap")
    @Select("select * from userInfo where id = #{id}")
    UserInfo selectOne(Integer id);

    
}

右键,generate,test.勾选.ok 

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.List;

import static org.junit.jupiter.api.Assertions.*;

@Slf4j
@SpringBootTest
class UserInfoMapperTest {
    @Autowired
    private UserInfoMapper userInfoMapper;
   
    @Test
    void selectOne() {
        log.info(userInfoMapper.selectOne(1).toString());
    }
}

成功