Fix for unexpected :time column behavior in Rails 3.2

dst_helper.rb

module DstHelper
  # Have a Time inherit DST status from a Date.
  def inherit_dst date, time
    time = time.change(:year => date.year, :month => date.mon, :day => date.day)
  end
  
  def self.included includer
    # Mix in class methods.
    includer.extend ClassMethods
  end
  
  module ClassMethods
    # For ActiveRecord models only.
    def applies_dst options={:from => nil, :to => nil}
      from = options[:from]
      to = options[:to]
      
      define_method("#{to}=") do |new_value|
        # Clear date information away from a Time object, so the correct value
        # is returned without having to #reload the object.
        self[to] = new_value.change :year => 2000, :month => 1, :day => 1
      end
      
      define_method(to) do
        from_value = self[from]
        to_value = self[to]
        
        if from_value and to_value
          inherit_dst(from_value, to_value).in_time_zone
        else
          # "Raw" value.
          to_value.in_time_zone
        end
      end
    end
  end
end

Create a file at lib/dst_helper.rb with the above code. Apply in your models by doing this:

class MyModel < ActiveRecord::Base
  include DstHelper

  applies_dst :from => :date, :to => :time
end

Now, when you access my_model.time, you'll get what you expect.