Simple solution to enable transaction rollbacks

application_controller.rb

class ApplicationController < ActionController::Base

  around_filter :check_dry_run
  
  def check_dry_run
    ActiveRecord::Base.transaction do
      yield
      raise ActiveRecord::Rollback, "dry_run specified; no changes made" if @dry_run
    end
  end
end

sample_controller.rb

class SampleController < ApplicationController
  def create
    if params[:dry_run].blank?
      @dry_run = true
    else
      @dry_run = false
    end
    
    @sample = Sample.new params[:sample]
    @sample.save
    
    respond_with @sample
    
  end

end