有時候為了簡化我們的代碼。

1 舉個例子

Student類：

@Datapublic class Student { private Integer id; private Integer age; private Integer sno;}

有時候我們想通過age這個屬性獲取Student對象

有時候我們也想通過sno這個屬性獲取Student對象

難道我們在DAO層寫兩個接口？

比如這樣子？

Student getStudentByAge(Int age);

Student getStudentBySno(Int sno);

那么在mapper文件中要這樣寫？

<select parameterType='int' resultMap='studentMap'> select * from student where age=#{age} </select> <select parameterType='int' resultMap='studentMap'> select * from student where sno=#{sno} </select>

顯然，這樣子是不高效的

2 上手測試 實驗

實體類 Student：

@Datapublic class Student { @ApiModelProperty(name = 'id',example = '1',position = 1) private Integer id; @ApiModelProperty(name = 'age',value = '年齡',example = '18',position = 2) private Integer age; @ApiModelProperty(name = 'sno',value = '學號',example = '334',position = 3) private Integer sno;}

數據庫：

CREATE TABLE `student` ( `id` int(11) NOT NULL AUTO_INCREMENT, `age` int(11) DEFAULT NULL COMMENT ’年齡’, `sno` int(11) NOT NULL COMMENT ’學號’, PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

手動添加一些數據

Dao層：

@Mapperpublic interface StudentDao { /** * @description: 通過student中的屬性 查詢到student * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: student **/ Student getStudent(Student student); /** * @description: 通過age sno 屬性來刪除 * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: void **/ void deleteStudent(Student student);}

Mapper

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE mapper PUBLIC '-//mybatis.org//DTD Mapper 3.0//EN' 'http://mybatis.org/dtd/mybatis-3-mapper.dtd' ><mapper namespace='com.dao.StudentDao'> <resultMap type='com.entity.Student'> <id property='id' column='id'/> <result property='age' column='age'/> <result property='sno' column='sno'/> </resultMap> <select parameterType='com.entity.Student' resultMap='studentMap'> select * from student where <if test='age != null'>age=#{age}</if> <if test='sno !=null'>sno=#{sno}</if> </select> <delete parameterType='Student'> delete from student <where> <if test='age != null'> age =#{age} </if> <if test='sno != sno'> sno=#{sno} </if> </where> </delete></mapper>

Service層：

@Servicepublic class StudentService { @Autowired StudentDao studentDao; /** * @description: 通過student中的屬性 查詢到student * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: student **/ public Student getStudent(Student student){ return studentDao.getStudent(student); } /** * @description: 通過age sno 屬性來刪除 * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: void **/ public void deleteStudent(Student student){ studentDao.deleteStudent(student); }}

Controller:

@RestController@Api('學生接口')@RequestMapping('/student')public class StudentController { @Autowired StudentService studentService; /** * @description: 通過student中的屬性 查詢到student * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: student **/ @ApiOperation('通過屬性查詢student') @PostMapping('/getStudent') Student getStudent(@RequestBody Student student){ return studentService.getStudent(student); } /** * @description: 通過age sno 屬性來刪除 * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: void **/ @ApiOperation('通過屬性刪除student') @PostMapping('/delete') public void deleteStudent(@RequestBody Student student){ studentService.deleteStudent(student); }}

3 直接測試

通過age屬性查詢student：成功

通過sno屬性查詢:

通過屬性age刪除Student:

通過sno屬性刪除Student

補充知識：mybatis使用if條件判斷，數字類型不能寫 0 ！=‘’，否則會進不到條件拼接里面

1.對于 if條件判斷：數字類型屬性判斷的時候

注意不可以是這種情況

<if test='delFlag!= null and delFlag!= ’’'> and del_flag = #{delFlag}</if>

參數一個是0，一個是''，最終debug會走進case 8 里面，0和“”都會被轉成double進行比較，都會變成0.0，這就是mybati中if test 0!=''判定為false的原因

以上這篇mybatis通過if語句實現增刪改查操作就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持好吧啦網。