Rails 4 - Combining scopes in a DRY manner

Question

Lets say I have this 3 scopes:

scope :assembly_reclamation, -> { where(status: 5) }
scope :customer_reclamation, -> { where(status: 9) }
scope :wrong_delivery,       -> { where(status: 12) }

Now let's say that I want to make a scope that joins those 3 categories. I am doing it right now like this:

scope :returnable, -> { where(status: [5, 9, 12]) }

While this works, it has some disadvantages. if I were to change the conditions of one of the 3 categories, I would have to rework the scope that contains them all as well.

Something like this seems more DRY:

scope :returnable, -> { assembly_reclamation.or.customer_reclamation.or.wrong_delivery }

But this is not valid code.

Is there a way to code it in such a fashion?

UPDATE

I know I have used an example using categories and ids, but please do not make it about it. It is about merging scopes.

UPDATE 2 I have changed the name of the attributes from idto status, because everyone was concentrating on the issue of the id, and that is not the point of the question

Answer 1

If you really are dealing with category_ids, it would be more meaningful for anyone, who reads the code if you have these ids as constants in Category model:

class Category
  ASSEMBLY_RECLAMATION_ID = 5
  CUSTOMER_RECLAMATION_ID = 9
  WRONG_DELIVERY_ID       = 12
  RETURNABLE_IDS          = [ASSEMBLY_RECLAMATION_ID, CUSTOMER_RECLAMATION_ID, WRONG_DELIVERY_ID]
end

From now on, you can use these constants in your scopes, and only change the constants, not scopes' implementation.

P.S. Rails 5 added OR support, but it's not that relevant for you until you upgrade.

EDIT

One way to combine few scopes is as follows:

scope :returnable, lambda {
  where(id: assembly_reclamation.ids + customer_reclamation.ids + wrong_delivery.ids)
}