string_nullifier.rb

# Include in ActiveRecord::Base to have your models automatically convert 
# empty strings and the like to nil before save.
module StringNullifier
  def self.included(model)
    model.class_eval do
      extend StringAttributesAccessor
      before_validation :nullify_strings
    end
  end
  
  module StringAttributesAccessor
    def string_attributes
      columns.select { |c| c.type == :string }.map { |c| c.name.to_sym }
    end
  end
  
private
  def nullify_strings
    self.class.string_attributes.each do |attribute|
      if (v = send attribute) and v.is_a?(String) and v.strip.empty?
        send "#{attribute}=", nil
      end
    end
  end
end