Question

I have a Payment Model which is polymorphic on activities

class Payment
  belongs_to :activity, polymorphic: true
end

one of the activities is referrals.

class Referral
  has_many :payments, :as => :activity

  def self.unpaid
    where(payments.count == 0)
  end
end

I want to create a class method so I can get all of the referrals which are unpaid. I was using this approach above, but getting a undefined_method error on payments.
Referral.first.payments.count works fine.

what am I missing here?

Answer 1

It sounds to me what you’re looking for are ActiveRecord Scopes. Using a scope, you’d do something like this:

class Referral
  has_many :payments, :as => :activity

  scope :unpaid, includes(:payments).where('payments.id is null')
end

This will perform a join on payments, and then the condition will find all columns that have no payments.id (in other words, with no payments). Then you could do Referral.unpaid.all, and see all referrals where there are no joined payments.