CODEWITHSUNDEEP
ruby-on-railscachingtags
Kelly
Kelly

Reputation: 41551

Does Rails have tags for expiring a cache?

Our app uses Rails.cache in the controller to cache some items outside the scope of the view (like meta tags), then uses fragment_caching on the bulk of the view.

The view caches one main model, but we have used data from 5 other models (not connected by an Association) inside that main cache. It's easy to expire the fragment with a sweeper on the main model, but those additional models also change and need to trigger this page to expire.

We can't use a regexp route for deleting the cache keys because we have to reference this cache entry by only the main model -- the other models are determined by an expensive query that we perform inside the cache block in the controller.

Does Rails 3 have a way to essentially use tags to mark a cache entry, so we can trash it when any of the 6 models on the page change, but we can still find the cache entry from only the main model's key?

Here's some dummy code to express the idea:

In the controller

@cache_key = "/page/#{params[:name]}/#{params[:id]}"
unless fragment_exist? ( { :slug => @cache_key })
  # run our processes here that will be needed in the view, 
  # then cache the data that is used outside the view
  Rails.cache.write(@cache_key, { (data goes here) } )
  # run our expensive query here:
  @similar_pages = Page.pricey_query!.limit(5).all
else 
  cached = Rails.cache.read(@cache_key)
end

In the view

- cache( {:slug => @cache_key} ) do
 - @similar_pages.each do |page|
  = image_tag page.photos.first.image.url
  -# more pretty stuff here

My goal:

Upvotes: 3

Views: 1160

Answers (3)

a moose
a moose

Reputation: 311

Cashier may be helpful. "Tag based caching"

# in your view
cache @some_record, :tag => 'some-component'

# later
Cashier.expire 'some-component'

https://github.com/twinturbo/cashier

Upvotes: 0

Kelly
Kelly

Reputation: 41551

Just as tadman states in the comments of the question, I had to invent my own solution, since Rails doesn't technically allow tags in the sense that I needed them. Here's a generalized solution for those interested in doing something similar:

I created a new table called SimilarPages:

create_table :similar_pages, {:id => false} do |t|
  t.integer :page_id, :similar_page_id
  # you could also do `t.string :tag_name` or similar
end
add_index :similar_pages, :page_id
add_index :similar_pages, :similar_page_id

Technically, I could do a self-referential has_many relationship on Pages, but I decided not to since I don't ever need to reference it that way. I just created a simple SimilarPage model:

class SimilarPage < ActiveRecord::Base
  belongs_to :page
  belongs_to :similar_page, :class_name => 'Page'
end

Then using ar-extensions (because I'm lazy, and also because I wanted to do this in one INSERT statement), I do this within the cache block:

SimilarPage.delete_all("page_id = '#{@page_id}'")
SimilarPage.import [:page_id, :similar_page_id], @similar_pages.collect {|s| SimilarPage.new(:page_id=>@page_id,:similar_page_id=>s.id)}

In my expire_cache_for method of my Observer, I do this:

SimilarPage.where(:similar_page_id => expiring_page.id).all.each do |s|
  ActionController::Base.new.expire_fragment(/page_show__#{s.page_id}__.*/) 
  # the regexp is for different currencies being cached ^
  Rails.cache.delete("page_show_#{s.page_id}")
end

Upvotes: 2

Jason Yost
Jason Yost

Reputation: 4937

There is an excellent explanation of how Rails generates tags for content expiration in this video http://railslab.newrelic.com/2009/02/19/episode-8-memcached

The short if it is if you pass your entire object into the cache it will generate a cache key that that uses the timestamp which will get updated when you change your object.

Upvotes: 0

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