mybatis-plus多表联查join的实现

<dependency>
            <groupId>com.github.yulichang</groupId>
            <artifactId>mybatis-plus-join</artifactId>
            <version>1.2.4</version>
        </dependency>

@Data
public class User {
  //对应数据库的主键（uuid，自增id，雪花算法,redis，zookper）
  @TableId(type = IdType.AUTO)
  private Integer id;

  @NotNull(message = "名称xxx不能为空")//空校验
  @NotBlank //不能为空字符串
  @Size(min = 1,max = 5,message = "ssssss")//字符串长度校验
  private String name;

//  @Min(value = 10,message = "最小值10")
//  @Max(value = 90,message = "最大值为99")

  @NotNull
//  @Max(value = 50,message = "超过最大值")
//  @Min(value = 10,message = "超过最小值")
  @Range(min=10,max = 99,message = "错误")//数字范围校验
  private Integer age;
  @NotNull
  private String email;


  //逻辑删除字段
  @TableLogic //逻辑删除注解
  private Integer deleted;

  //字段添加填充内容
  //策略
//  @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
  @TableField(fill = FieldFill.INSERT)

  @DateTimeFormat(pattern = "yyyy-MM-dd")
  @JsonFormat(pattern = "yyyy-MM-dd", timezone = "GMT+8")
  private LocalDateTime createTime;
  //策略
//  @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")

  @JsonFormat(pattern = "yyyy-MM-dd", timezone = "GMT+8")
  @TableField(fill = FieldFill.INSERT_UPDATE)
  private LocalDateTime updateTime;

  @TableField(fill = FieldFill.INSERT)
  private Integer createBy;

  @TableField(fill = FieldFill.INSERT_UPDATE)
  private Integer updateBy;

  @Version//乐观锁注解
  private Integer version;

}

@Data
public class UserScore {
    @TableId(type = IdType.AUTO)
    private long id;
    private String course;
    private String score;
    private Long userId;
}

@Data
public class UserCourseTeacher {
    @TableId(type = IdType.AUTO)
    private Integer id;

    private Long teacher;

    private Long userCourseId;
}

@Repository
@Mapper
public interface UserMapper extends MPJBaseMapper<User> {
}

@Repository
@Mapper
public interface UserScoreMapper extends MPJBaseMapper<UserScore> {
}

@Mapper
@Repository
public interface UserCourseTeacherMapper extends MPJBaseMapper<UserCourseTeacher> {
}

@Data
public class UserTeacherDto extends User {
    private String course;
    private String score;
    private String teacher;
}

select a.*,b.score,b.course,c.teacher from user a left join user_score b on a.id=b.user_id left join user_course_teacher c on b.id=c.user_course_id

public List<UserTeacherDto> GetAllUserTeacher(){
        MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>()
                .selectAll(User.class)
                .select(UserScore::getScore,UserScore::getCourse)
                .select(UserCourseTeacher::getTeacher)
                .leftJoin(UserScore.class,UserScore::getUserId,User::getId)
                .leftJoin(UserCourseTeacher.class,UserCourseTeacher::getUserCourseId,UserScore::getId);
        List<UserTeacherDto> list=userMapper.selectJoinList(UserTeacherDto.class, mPJLambdaWrapper);
        return list;
    }

@Override
    public Map<String,Object> GetUserDtoByPage(){
        Map<String,Object> result=new HashMap<>();
        MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>()
                .selectAll(User.class)
                .select(UserScore::getScore,UserScore::getCourse)
                .leftJoin(UserScore.class,UserScore::getUserId,User::getId);

        IPage<UserDto> UserDtoPage=userMapper.selectJoinPage(
                new Page<UserDto>(3,2),
                UserDto.class,
                mPJLambdaWrapper
        );
        result.put("list",UserDtoPage.getRecords());
        result.put("count",UserDtoPage.getTotal());
        return result;
    }

MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>()
                .selectAll(User.class)

@Override
    public List<UserTeacherDto> GetAllUserTeacher(Map<String,Long> params){
        System.out.println("传递参数");
        System.out.println(params.get("id"));
        MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>()
                .selectAll(User.class)
                .select(UserScore::getScore,UserScore::getCourse)
                .select(UserCourseTeacher::getTeacher)
                .leftJoin(UserScore.class,UserScore::getUserId,User::getId)
                .leftJoin(UserCourseTeacher.class,UserCourseTeacher::getUserCourseId,UserScore::getId);
        if(params.get("id")!=null && params.get("id").toString()!=""){
            mPJLambdaWrapper.eq(UserScore::getId,params.get("id"));
        }
        List<UserTeacherDto> list=userMapper.selectJoinList(UserTeacherDto.class, mPJLambdaWrapper);
        return list;
    }