关注模块面经文档#

【写流程：推模式】

用户发布新笔记
    │
    ▼
查询该用户的所有粉丝列表（从 MySQL tb_follow 查询）
    │
    ▼
遍历每个粉丝，将笔记 ID 写入粉丝的收件箱
    ZADD feed:{粉丝ID} {当前时间戳} {笔记ID}
    │
    └── 每个粉丝都有独立的 ZSet 收件箱

【读流程：滚动分页】

用户刷新关注页
    │
    ▼
ZREVRANGEBYSCORE feed:{userId} {max} 0 LIMIT {offset} 2
    │
    ├── 返回笔记 ID 列表
    ├── 记录本次最小 score（minTime）
    └── 记录与 minTime 相同 score 的个数（offset，用于下次跳过重复）
    │
    ▼
根据笔记 ID 查询笔记详情返回

@Override
public Result follow(Long followUserId, Boolean isFollow) {
    Long userId = UserHolder.getUser().getId();
    String key = "follows:" + userId;  // Redis Set key

    if (isFollow) {
        // 关注：写 DB + 写 Redis
        Follow follow = new Follow();
        follow.setUserId(userId);
        follow.setFollowUserId(followUserId);
        boolean isSuccess = save(follow);
        if (isSuccess) {
            stringRedisTemplate.opsForSet().add(key, followUserId.toString());
        }
    } else {
        // 取关：删 DB + 删 Redis
        boolean isSuccess = remove(new QueryWrapper<Follow>()
            .eq("user_id", userId)
            .eq("follow_user_id", followUserId));
        if (isSuccess) {
            stringRedisTemplate.opsForSet().remove(key, followUserId.toString());
        }
    }
    return Result.ok();
}

@Override
public Result followCommons(Long targetUserId) {
    Long userId = UserHolder.getUser().getId();
    String key1 = "follows:" + userId;
    String key2 = "follows:" + targetUserId;

    // Redis SINTER 求交集，返回两个用户共同关注的 ID 集合
    Set<String> intersect = stringRedisTemplate.opsForSet().intersect(key1, key2);

    if (intersect == null || intersect.isEmpty()) {
        return Result.ok(Collections.emptyList());
    }

    // 解析 ID，批量查询用户信息
    List<Long> ids = intersect.stream().map(Long::valueOf).collect(Collectors.toList());
    List<UserDTO> users = userService.listByIds(ids)
        .stream()
        .map(user -> BeanUtil.copyProperties(user, UserDTO.class))
        .collect(Collectors.toList());

    return Result.ok(users);
}

@Override
public Result saveBlog(Blog blog) {
    UserDTO user = UserHolder.getUser();
    blog.setUserId(user.getId());
    boolean isSuccess = save(blog);
    if (!isSuccess) {
        return Result.fail("新增笔记失败!");
    }

    // 查询作者的所有粉丝
    List<Follow> follows = followService.query()
        .eq("follow_user_id", user.getId()).list();

    // 推送笔记 ID 到每个粉丝的 ZSet 收件箱
    for (Follow follow : follows) {
        Long fanId = follow.getUserId();
        String key = FEED_KEY + fanId;   // feed:{fanId}
        stringRedisTemplate.opsForZSet()
            .add(key, blog.getId().toString(), System.currentTimeMillis());
    }
    return Result.ok(blog.getId());
}