Question

I’m trying to increase performance in my application by caching database queries. These are simple queries since I need to load and cache all objects.

Here’s a shortened version of my application_controller.rb:

class ApplicationController < ActionController::Base
  protect_from_forgery

  def show_all
    load_models
    respond_to do |format|
      format.json { render :json => {"items" => @items}
      }
    end
  end

  protected    
  def load_models
    @items = Rails.cache.fetch "items", :expires_in => 5.minutes do
      Item.all
    end
  end
end

But when I try and load this page I get this error:

ArgumentError in ApplicationController#show_all
undefined class/module Item

I’ve been following low-level caching guides by Heroku posted here: https://devcenter.heroku.com/articles/caching-strategies#low-level-caching

Any ideas what I can do here to get caching working? Is there a better way to accomplish this?

Answer 1

I fixed this issue by storing encoded JSON in Rails.cache.fetch instead of the raw ActiveRecord objects. I then retrieve the stored JSON, decode it, and render it for the view. The finished code looks like this:

  def show_all
    json = Rails.cache.fetch "Application/all", :expires_in => 5.minutes do
      load_models
      obj = { "items" => @items }
      ActiveSupport::JSON.encode(obj)
    end

    respond_to do |format|
      format.json { render :json => ActiveSupport::JSON.decode(json) }
    end
  end

  def load_models
    @items = Item.all
  end