If the news has an ID or unique identifier. You can consider using the redis collection type. And the uniqueness of the collection prevents duplicate addition problems!
redis.sadd('personmark:userID',newsID);//Add an element to the user collection
redis.smembers('personmark:userID');//Get all the news IDs collected by the user at once

Use sorted set zset;
key is user ID;
member is the unique ID of the news;
Score is the date increment starting from a previous day (for example, starting from 2015-1-1, today's score is 155?); once you have the score, you can take it out without sorting and display it directly;
zadd(key, score, member)：Add news
zrank(key, member): Returns according to score from small to large, that is, the collected news is sorted by date from new to old;
zrangebyscore(key, min, max): Returns the set of scores from start to end, used to realize page turning display of news;

key: news_fav_uid
value: a collection of news IDs (array)
where uid is the user ID.
$news_ids = array(1024,1025,1026);
echo json_encode($news_ids);
No matter you are using Memcached/Redis/MySQL, you can store it like this.
array_push pushes new collections to the end of the $news_ids array.
If you want to sort by time, you only need json_decode to decode, array_reverse to flip the array, and then foreach to output.

The answer on the 1st floor is very good, but I just want to add that there is no need to use redis as a cache here, just use it as a data storage, because redis is also a database