实体新增id字段

package com.ruoyi.system.domain;

public class Student {

    private Integer id;
    /**
     * 学生姓名
     */
    private String name;
    /**
     * 学生年龄
     */
    private Integer age;
    /**
     * alt+insert生成get,set方法
     */
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }
}

controller

package com.ruoyi.web.controller.system;

import com.ruoyi.system.domain.Student;
import com.ruoyi.system.service.StudentService;
import org.apache.xmlbeans.impl.xb.xsdschema.Public;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

@RestController
@RequestMapping("student/student")
public class StudentController {
    @Autowired
    private StudentService studentService;
    @GetMapping("list")
    /**
     * alt+回车找到对应的包
     */
    public Map<String,Object> list(){
        List<Student> lst = studentService.list();
        Map<String,Object> map = new HashMap<>();
        map.put("data",lst);
        return map;
    }
    /**
     * 实现删除功能接口
     * delete from student where id = 5
     */
    @GetMapping("delete")
    public Map<String,Object> delete(Integer id){
        Integer ss = studentService.delete(id);
        System.out.println(ss);
        Map<String,Object> map = new HashMap<>();
        map.put("msg","删除数据成功!");
        map.put("code",200);
        return map;
    }
    /**
     * 实现添加接口
     * INSERT INTO `student`( `name`, `age`) VALUES ('eageg', 3);
     */
    @PostMapping("add")
    /**前端给后端传递的参数
     * {
     * 	"name" : "小是",
     * 	"age" : 1
     * }
     */
    public Map<String,Object> add(@RequestBody Student student){
        Integer ss = studentService.add(student);
        System.out.println(ss);
        Map<String,Object> map = new HashMap<>();
        map.put("msg","添加数据成功!");
        map.put("code",200);
        return map;
    }
    /**
     * 修改接口
     * UPDATE `student` SET `name` = '小是', `age` = 1 WHERE `id` = 14;
     */
    @PostMapping("update")
    public Map<String,Object> update(@RequestBody Student student){
        Integer ss = studentService.update(student);
        System.out.println(ss);
        Map<String,Object> map = new HashMap<>();
        map.put("msg","修改数据成功!");
        map.put("code",200);
        return map;
    }
    /**
     * 根据id查询所有数据
     *select * from student where id = 14
     */
    @GetMapping("selectById")
    public Map<String,Object> selectById(Integer id){
        List<Student> lst = studentService.selectById(id);
        Map<String,Object> map = new HashMap<>();
        map.put("data",lst);
        return map;
    }
}

serviceImpl

package com.ruoyi.system.service.impl;

import com.ruoyi.system.domain.Student;
import com.ruoyi.system.mapper.StudentMapper;
import com.ruoyi.system.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class StudentServiceImpl implements StudentService {
    @Autowired
    private StudentMapper studentMapper;
    @Override
    public List<Student> list() {
        return studentMapper.list();
    }

    @Override
    public Integer delete(Integer id) {
        return studentMapper.delete(id);
    }

    @Override
    public Integer add(Student student) {
        return studentMapper.add(student);
    }

    @Override
    public Integer update(Student student) {
        return studentMapper.update(student);
    }

    @Override
    public List<Student> selectById(Integer id) {
        return studentMapper.selectById(id);
    }

}

mapper

package com.ruoyi.system.mapper;

import com.ruoyi.system.domain.Student;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface StudentMapper {
    List<Student> list();

    Integer delete(Integer id);

    Integer add(Student student);

    Integer update(Student student);

    List<Student> selectById(Integer id);
}

xml

<?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.ruoyi.system.mapper.StudentMapper">

    <resultMap type="Student" id="SysUserResult">
        <result property="id"     column="id"      />
        <result property="name"     column="name"      />
        <result property="age"     column="age"      />
    </resultMap>
    <insert id="add" parameterType="Student">
        INSERT INTO `student`( `name`, `age`) VALUES (#{name}, #{age});
    </insert>
    <update id="update" parameterType="Student">
        UPDATE `student` SET `name` = #{name}, `age` = #{age} WHERE `id` = #{id};
    </update>
    <delete id="delete" parameterType="int">
        delete from student where id = #{id}
    </delete>
    <select id="list" resultMap="SysUserResult">
        SELECT * FROM `student`
    </select>
    <select id="selectById" resultMap="SysUserResult">
        select * from student where id = #{id}
    </select>

</mapper>