mybatis通过if语句实现增删改查操作
有个机车梦 人气:0有时候为了简化我们的代码。
1 举个例子
Student类:
@Data public 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 id="getStudentByAge" parameterType="int" resultMap="studentMap"> select * from student where age=#{age} </select> <select id="getStudentBySno" 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:
@Data public 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:
@Mapper public 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 id="studentMap" type="com.entity.Student"> <id property="id" column="id"/> <result property="age" column="age"/> <result property="sno" column="sno"/> </resultMap> <select id="getStudent" 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 id="deleteStudent" 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:
@Service public 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
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