delete Paperclip attachment unless it is the last one

I have a rails app with the follow code:

class Rig < ActiveRecord::Base
  has_many :rig_pictures, :dependent => :destroy

  accepts_nested_attributes_for :rig_pictures, 
                                :allow_destroy => true,
                                #we reject blank pictures unless they have to be deleted
                                :reject_if => lambda { |a| a['picture'].blank? && !a['_destroy'] }

  validate :has_beween_1_and_x_pictures
private

  def has_beween_1_and_x_pictures
    errors.add_t开发者_StackOverflow中文版o_base("must not have more than 8 pictures") if rig_pictures.size > 8
    errors.add_to_base("must have at least 1 picture") if rig_pictures.size < 1
  end
end

My problem is the "must have at least 1 picture" validation. If the user is in the Edit form and delete all his picture, the validation will not fail because at that point, it does not know what I want to delete it.

So my question is: how can I make sure the validation only considers the real pictures and not those I want to delete?

Thx.

Maybe You could try a validation in the RidPicture Model .

Something similar to

def before_destroy
    if ( self.rid.rid_pictures.count <= 1)
      errors.add_to_base  "Almost one image"
      false
    end 
end

not tested