Question

I know you can do:

validates :cat_no, :presence => true, :on => :create

I have a custom action:

 def approve
    @product = Product.find(params[:id])
    @product.update_attribute :approved, true
    redirect_to product_path(@product)
 end

And i’d like to do:

validates :cat_no, :presence => true, :on => :approve

This doesn’t seem to work. Is there a simple way of doing this?

Answer 1

I think you’re misunderstanding the idea of validations. Validations are triggered by changes to the model (via save, create or update), not by controller actions, so it doesn’t make sense in your case to have your approved action trigger a validation.

Looking at your code, it seems to me what you really want to do is run a validation on cat_no when the model is updated, on the condition that the value of approved has just become true (i.e. line 2 of your approve action where you have @product.update_attribute :approved, true).

I think the code below should achieve that:

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

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

UPDATE:

In retrospect, the validation above is probably more permissive than what you’d actually want to have. If you have an approved record and you change cat_no to nil, it will validate because approved has not changed (so changed.include?("approved") will evaluate to false).

More likely this is what you actually want:

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