mybatis通过if语句实现增删改查操作

有时候为了简化我们的代码。

1 举个例子

Student类：

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

有时候我们想通过age这个属性获取Student对象

有时候我们也想通过sno这个属性获取Student对象

难道我们在DAO层写两个接口？

比如这样子？

Student getStudentByAge(Int age);

Student getStudentBySno(Int sno);

那么在mapper文件中要这样写？

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

显然，这样子是不高效的

2 上手测试 实验

实体类 Student：

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

数据库：

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

手动添加一些数据

Dao层：

@Mapperpublic interface StudentDao { /** * @description: 通过student中的属性 查询到student * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: student **/ Student getStudent(Student student); /** * @description: 通过age sno 属性来删除 * @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层：

@Servicepublic class StudentService { @Autowired StudentDao studentDao; /** * @description: 通过student中的属性 查询到student * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: student **/ public Student getStudent(Student student){ return studentDao.getStudent(student); } /** * @description: 通过age sno 属性来删除 * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: void **/ public void deleteStudent(Student student){ studentDao.deleteStudent(student); }}

Controller:

@RestController@Api('学生接口')@RequestMapping('/student')public class StudentController { @Autowired StudentService studentService; /** * @description: 通过student中的属性 查询到student * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: student **/ @ApiOperation('通过属性查询student') @PostMapping('/getStudent') Student getStudent(@RequestBody Student student){ return studentService.getStudent(student); } /** * @description: 通过age sno 属性来删除 * @param: student * @author: Yuz * @creat_time: 2019/8/20 * @return: void **/ @ApiOperation('通过属性删除student') @PostMapping('/delete') public void deleteStudent(@RequestBody Student student){ studentService.deleteStudent(student); }}

3 直接测试

通过age属性查询student：成功

通过sno属性查询:

通过属性age删除Student:

通过sno属性删除Student

补充知识：mybatis使用if条件判断，数字类型不能写 0 ！=‘’，否则会进不到条件拼接里面

1.对于 if条件判断：数字类型属性判断的时候

注意不可以是这种情况

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

参数一个是0，一个是''，最终debug会走进case 8 里面，0和“”都会被转成double进行比较，都会变成0.0，这就是mybati中if test 0!=''判定为false的原因

以上这篇mybatis通过if语句实现增删改查操作就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持好吧啦网。