Question

So right now users have a list of items that changes, but not too often, so I decided to keep it in a cache like so:

  #Fetch the cache
  def self.fetch_cache(user)
    Rails.cache.fetch(user.items, :expires_in => 15.minutes) do
      user.items.order("created_at ASC").all
    end    
  end

This works if the user has items. The problem is, if the user doesn’t have any items (because they’re a new user or something) and the cache will return an error.

How should I be using this to make it work for users with nothing?

Thanks!

Answer 1

You’re using a really weird cache key there (the first argument to Rails.cache.fetch). You’re supposed to be passing a string that identifies the cache entry but you’re passing in an association.

Rails is probably helpfully calling to_s on user.items in order to turn it into a string that but that’s not a useful cache key as you’re going to have to load the user’s items in order to compute the cache key to get the users’ items from the cache!

Something like "user_#{user.id}_items" would be a far better cache key.