Rails expire low level cache on update - ruby-on-rails

Question

I am using Rails low level cache in my controller but I don't know how to expire the cache when record is updated. Below is snippets of my controller
def show
#user = Rails.cache.fetch("users/params[:id]", expires_in: 2.minutes) do
User.find(params[:id])
end
end
So rails is creating cache fine. But when I update the record I want to expire old cache and create new one. e.g
User.first.touch
I found that rails have cache_key_with_version but I am not sure how to use that with my example
#user = User.first
#user.cache_key_with_version #=> "users/1-20220316023452830286"
I won't have #user object at the first call in my controller so I am not sure how to use #user.cache_key_with_version as my key.
#user = Rails.cache.fetch(#user.cache_key_with_version)
Above code will not work as #user is nil at this stage.
One way I can think of is use after_save callback in model to delete cache key on save. Some thing like this
class User < ApplicationRecord
after_save :delete_cache_key
private
def delete_cache_key
Rails.cache.delete("users/#{self.id}")
end
end
But may be there is better way to solve this.

Answer 1

If you want Rails to get expired when record update, add cache_key_with_version to your cache key, so the controller will be like
def show
#user = User.find(params[:id])
Rails.cache.fetch("users/#{#user.cache_key_with_version}", expires_in: 2.minutes) do
# some other query that need to be done
end
end
loading a record should not be a heavy load, if it is, than use .select(:id, :updated_at) may be a choice
def show
user_cache_key = User.select(:id, :updated_at).find(params[:id]).cache_key_with_version
#user = Rails.cache.fetch("users/#{user_cache_key}", expires_in: 2.minutes) do
User.find(params[:id])
end
end
cache key is made with updated_at and id, so we only these two column to make a cache key with version. When record update, it will update updated_at, too, the previous cache will be discarded