conditional validate

http://stackoverflow.com/questions/11882497/rails-validation-on-custom-action

validates :cat_no, :presence => true, :on => :update, :if => :just_approved?

def just_approved?
  changed.include?("approved") && approved?
end

js validation

http://railsadventures.wordpress.com/2012/10/21/using-rails-remote-forms-with-jquery-validations/

以下も参考して

• 2014-02-14-jquery-validate
• 2014-02-24-promise-deferred