Redis-存储用户喜欢

Question

I'm currently learning Redis, and I want to show to the user if he already liked a post or not, like on facebook.

I was thinking of storing a list of users id, something like this:

$redis.rpush('users_liked_post_#{post_id}', user_id)

$redis.lrange('users_liked_post_#{post_id}', 0, -1)

# [34, 23, 433, 432, 324]

And then check if the user id is in that list to tell if he already liked the post. But it's a O(n) speed, is there a better way ?

Answer 1

Use a Set instead - it ensure no duplicates (ie a user can't like a post twice) and you can check existence quickly, ie (assuming redis-rb):

redis.sadd 'post:{#post_id}:likes', '{#user_id}'

Note that in order to do the reverse query, get the list of pages that a user liked, you'll need to keep another Set with the likes per each user, eg:

redis.sadd 'user:{#user_id}:likes' '{#post_id}'