gistfile1.rb

module SelectiveAttributeValidatable

  def self.included(base)
    base.send(:include, InstanceMethods)

    base.class_eval do
      alias_method_chain :update_attributes, :check
    end
  end

  module InstanceMethods

    # Store the set of attributes passed in to #update_attributes.
    def update_attributes_with_check(attrs)
      @attrs_to_validate = attrs.keys.map(&:to_s)
      update_attributes_without_check(attrs)
    end


    # Returns true if a given attribute was passed in to #update_attributes.
    def should_validate?(attr)
      if self.new_record?
        attrs_to_validate_on_create.include?(attr)
      else
        @attrs_to_validate.blank? || 
        @attrs_to_validate.include?(attr) || 
        self.status == 'ENABLED'
      end
    end

    # This method must be overwritten in the class
    # where this module is included. Specify whichever 
    # attributes you want validated on create:
    #   ['name', 'sku']
    def attrs_to_validate_on_create
      []
    end

    # Allows for the should_validate_x? condition 
    # in your validations.
    def method_missing(method, *args)
      if method.to_s =~ /^should_validate_([_\w]+)[?]/
        return should_validate?($1)
      else
        super
      end
    end

  end

end