CODEWITHSUNDEEP
redis
0xSina
0xSina

Reputation: 21553

Redis delete item in sorted set

I am using Redis to implement a 'feed' system in my social networking app similar to Instagram/facebook.

I have a key "user:id:feed" which contains a sorted set of ids that point to pictures. What I am wondering is, when a particular photo is deleted, how can I make sure that photo id is also deleted in all feeds that contain that photo id?

Would I have to loop through each and every feed set and delete it? Is that a common pattern in redis?

Thanks

Upvotes: 2

Views: 2334

Answers (1)

Didier Spezia
Didier Spezia

Reputation: 73226

The common pattern in Redis is to cross-reference items in various data structures. You have to do it explicitly (there is no automatic referential integrity mechanism with Redis).

Here you have a many-to-many relationship between feeds and photos. If you need to add/remove both feeds and photos, you will probably want to use 2 distinct data structures to materialize this relationship.

user:id:feed  ->  sorted sets of photo:n (referring to photos)
photo:n       ->  set of user:id:feed (referring to feeds)

So you can efficiently retrieve the photos from the feeds, and the feeds from the photos. For instance to delete a photo:

  • retrieve the feeds from photo:n
  • pipeline several ZREM operations (one per user:id::feed)

So the delete operation is finally costing two roundtrips. You can decrease to 1 roundtrip by using a Lua server-side script.

Upvotes: 2

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