gistfile1.rb

def used_promotion_credits(order)
    p = PromotionCredit.arel_table
    o = Order.arel_table

    if order.user.anonymous?
      user_condition = o[:email].eq order.email
    else
      user_condition = o[:user_id].eq order.user_id
    end
    
    PromotionCredit.includes(:order).where(p[:source_id].eq(promotion_id), o[:state].eq(Order::FINALIZED_STATES), user_condition)
  end