Rails accepts_nested_attributes_for with _destroy can skip presence validation

Question

So I have a typical Rails model with accepts_nested_attributes_for with presence validation

(snippets)

class Book < ActiveRecord::Base
  ...

  has_one :cover
  accepts_nested_attributes_for :cover, allow_destroy: true

  validate :require_cover

  def require_cover
    errors.add('', 'You must have a cover for the book.') if self.cover.blank?
  end

  ...
end

This works and validates okay on the first step when I'm creating. But when I try to edit it and click delete on the cover (clicking delete adds _destroy true) and save it, it deleted the cover but the validation regarding presence has passed already.

I think what happened was:

1. tagged destroy cover
2. validation process happens (thinks there is still cover (but maybe doesn't recognize destroy))
3. valid and goes to saving
4. saves book and
5. passes

No validation again regarding the no cover

Have I done this incorrectly? Is there another way to implement this? Or how do I revalidate this scenario (like, after the save and destroy that has happened, there would be another validation to say that the resulting object is now invalid)?

Answer 1

I found the fix to my question, I was right that the save doesn't take into account those that are tagged as _destroy.

This link describes the problem better and has the answer to it too. http://homeonrails.com/2012/10/validating-nested-associations-in-rails/

Basically he rejected those that are marked for destruction and counted the remaining ones.