How do I change an ActiveRecord from marked to be saved to make sure it does not get saved, from within the model itself?
before_save :ignore_new_delete_exisiting_if_blank(self.attribute)

def ignore_new_delete_exisiting_if_blank(attribute)
  self.do_not_save_me! if attribute.blank?

  #what is that magic "do_not_save_me" method?
  #Is there such thing, or something to achieve the same thing?
end

def ignore_new_delete_exisiting_if_blank_attribute
  if attribute.blank?
    errors.add(:base, "Not allowed to save if attribute is blank.")
  end
end

validates_presence_of :attribute

accepts_nested_attributes_for :posts, :reject_if => proc { |attributes| attributes['title'].blank? }

def ignore_new_delete_exisiting_if_blank(attribute)
  attribute.present?
end