解读controller层,service层,mapper层,entity层的作用与联系

@RestController
@RequestMapping("/user")
public class UserController {
 
    @Autowired
    private UserMapper userMapper;
    
    @GetMapping("/select")
    public List<User> index(){
        List<User> all = userMapper.findAll();
        return all;
    }
 
    @Autowired
    private UserService userService;
    @PostMapping("/insert")
    public boolean save(@RequestBody User user){
        return userService.saveUser(user);
    }
 
    @DeleteMapping("/{id}")
    public Integer delete(@PathVariable Integer id){
        return userMapper.deleteById(id);
    }

public class UserService extends ServiceImpl<UserMapper, User> {
        public boolean saveUser(User user) {
            if(user.getId() == null){
            return save(user);//mybatis-plus提供的方法，表示插入数据。
            }else{
            return updateById(user);
        }
}

@Mapper
@Repository
public interface UserMapper extends BaseMapper<User> {//数据库查询接口，专门用来跟数据库交互用的
    @Select("SELECT * from sys_user")
    public List<User> findAll();
 
    List<User> findAll1();
    @Insert("INSERT into sys_user(username,password,nickname,email,phone,address)VALUES(#{username},#{password},#{nickname}," +
            "#{email},#{phone},#{address});")
    public int insert(User user);
 
    public int updateUser(User user);
 
    @Delete("delete from sys_user where id = #{id}")
    public Integer deleteById(@Param("id") Integer id);

@Data//Data注解代替了get和set方法
@TableName(value = "sys_user")
public class User {
    @TableId(type = IdType.AUTO)
    private Integer id;
    private String username;
    private String password;
    private String nickname;
    private String email;
    private String phone;
    private String address;
}