Question

So I was wondering if we can have a conditional allow_nil option for a validation on a rails model.

What I would like to do is to be able to allow_nil depending upon some logic(some other attribute)

So I have a product model which can be saved as draft. and when being saved as draft the price can be nil, but when not a draft save the price should be numerical. how can I achieve this. The following doesn’t seem to work. It works for draft case but allows nil even when status isn’t draft.

class Product<ActiveRecord::Base
   attr_accessible :status, price
   validates_numericality_of :price, allow_nil: :draft?

   def draft?
     self.status == "draft"
   end

end

Looking at rails docs I looks like there isn’t an option to pass a method to allow_nil?

One possible solution is to do separate validations for both cases

 with_options :unless => :draft? do |normal|
    normal.validates_numericality_of :price
 end

 with_options :if => :draft? do |draft|
   draft.validates_numericality_of :price, allow_nil: true
 end

Any other ways to get this working ?

Thanks

Answer 1

You can use if and unless to do the following

class Product<ActiveRecord::Base
   attr_accessible :status, price
   validates_numericality_of :price, allow_nil: true, if: :draft?
   validates_numericality_of :price, allow_nil: false, unless: :draft?

   def draft?
     self.status == "draft"
   end

end

With the above, you will have 2 validations set up, one that applies when draft? == true, which will allow nils, and one where draft? == false which will not allow nils