How can I specify validation only for one model with polymorphic association?

Question

I have a polymorphic model command who can be associated to a cover or to an additional_return. Those are the field in command :

  create_table "commands", force: :cascade do |t|
    t.date     "placement_date"
    t.date     "estimated_delivery_date"
    t.string   "commandable_type"
    t.integer  "commandable_id"
    ...
  end

The thing is : for cover I would like to validate the estimated_delivery_date but not for the model additional_return. How can I specify a validation only for one model ?

 class Command < ApplicationRecord
   belongs_to :user, dependent: :destroy
   belongs_to :commandable, polymorphic: true
   validates_presence_of :commandable_type,
                         :commandable_id
 end

Answer 1

You could do something like this:

validates :estimated_delivery_date, presence: true, if: :date_required?

private
def date_required?
  commandable.is_a?(Cover)
end