the incandescent bulb

Note to self :

If you’re using fragment caching and you’re application is deployed to a hosting provider with multiple slices. don’t forget to define the location of the cache and store your cache in a location that all slices have access to. by default rails stores the cache in /tmp/cache , normally I would point it to RAILS_ROOT + tmp/cache

Here’s how to explicitly define the location of your cache:

Just need to define this in your environment.rb or create a file in the initializers directory.

ActionController::Base.fragment_cache_store = :file_store, "/path/to/cache/directory"

Some links about caching that I find very useful:

http://www.railsenvy.com/2007/2/28/rails-caching-tutorial
http://www.railsenvy.com/2007/3/20/ruby-on-rails-caching-tutorial-part-2

I came across this problem just today, it cost me about 30 minutes to 1 hour just figuring out what I did wrong not to mention the time I spent trying to look for the solution. Luckily I stumbled upon this ticket. here Apparently this problem has already been reported and a patch has already been submitted over a year ago. But it hasn’t been pushed to rails core yet. Anyways to summarize the situation, heres how one can stumble into this problem:

Lets say you have a view which uses the date helper datetime_select like so:

<% form_for(:ticket, :url => tickets_path) do |f| %>
  	 <%= f.text_field :title -%>
  	 <%= f.text_field :description -%>
  	 <%= f.datetime_select :date_this_ticket_might_get_resolved -%>
<% end %>

And here’s a sample controller:

class TicketsController < ApplicationController

	def	create
		@ticket = Ticket.new(params[:ticket])
		@ticket.save
	end

end

And lastly the model:

class Ticket < ActiveRecord::Base

  	 def date_this_ticket_might_get_resolved=(val)
    	 	self.date_of_submission = Time.mktime( val[:year], val[:month], val[:day],
                                            val[:hour], val[:minute]) + 1.year
  	 end

  	 def date_this_ticket_might_get_resolved
    	 	self.date_of_submission + 1.year # add another year just to be sure
  	 end

end

You will get something like this error:

NoMethodError (You have a nil object when you didn't expect it!The error occurred while evaluating nil.klass):
	/vendor/rails/activerecord/lib/active_record/base.rb:2645:in `execute_callstack_for_multiparameter_attributes'
	/vendor/rails/activerecord/lib/active_record/base.rb:2644:in `each'
	/vendor/rails/activerecord/lib/active_record/base.rb:2644:in `execute_callstack_for_multiparameter_attributes'
	/vendor/rails/activerecord/lib/active_record/base.rb:2630:in `assign_multiparameter_attributes'
	/vendor/rails/activerecord/lib/active_record/base.rb:2375:in `attributes='

I was using Rails 2.1 with Ruby 1.8.6 , The patch can be found on this link, Just follow the instructions its just a one liner change on ActiveRecord::Base.