Question

I have a controller action that calls a model method which generates a serialized list of data pulled from another model database. I need this to be uncached because the SQL queries should be random data pulls.

Here’s a general idea of my code (Note that User has_one Foo, Bar is an arbitrary model of data, :data_list is of type text, and the database is SQLite):

# app/models/foo.rb

class Foo < ActiveRecord::Base
  serialize :data_list

  def generate_data
    list = []
    for i in 1..4
      data = Bar.find(:first, :order => "Random()")
      list << data
    end
    self.data_list = list
  end
end

# app/controllers/users_controller.rb

class UsersController < ApplicationController
  def generate_action
    ...
    uncached do
      @user.foo.generate_data
    end
    @user.foo.save
  end
end

# app/views/user/show.html.erb

...
<% @user.foo.data_list.each do |data| %>
  <%= data %><br />
<% end %>

Whenever uncached do ... end is removed, everything works fine and the show view prints out each set of Bar objects in @user.foo.data_list. Unfortunately, because of Rails’ SQL caching, it ends up look like this:

RandomDataPoint8
RandomDataPoint8
RandomDataPoint8
RandomDataPoint8

When I need to look like this:

RandomDataPoint7
RandomDataPoint13
RandomDataPoint2
RandomDataPoint21

It should be noted that running user.foo.generate_data from Rails command line works perfectly with the randomization. It is only when being called from the controller that caching starts to occur.

My research suggested I use uncached in the controller to remove caching, however it seems to destroy my data serialization and I receive the error:

undefined method 'each' for #<String:0x007ff49008dc70>

In fact, it does this even if I retroactively add in uncached (having successfully generated a data_plan without uncached prior) and save the controller, but don’t call generate_action.

Answer 1

EDIT
I believe this problem is actually related to the fact that I was storing an object in the hash. Switching to the object id fixed this problem. Another SO question of mine regarding this can be found here:
Rails – Accessing serialized data from console

The following has been preserved just because the syntax may still help people, but I don’t believe it was the actual cause of the problem.

---

I solved this by moving uncached to the model. For reference, the source I was using to originally solve this problem was this link: http://railspikes.com/2008/8/18/disabling-activerecord-query-caching-when-needed

What I overlooked is that he puts uncached in the model, not the controller. Also, the syntax needed to be a little different:

# app/models/foo.rb

self.class.uncached do
   ...
end

instead of

uncached do
  ...
end

The source for the syntax correction is this SO response: https://stackoverflow.com/a/967690/337903