ActiveRecord fetching records from has_many and related relationship through scopes

Question

I have two models: Customer and Order . Sometimes it happens that two Customers are actually the same customer, which is indicated by one of them having a master_id which points to another Customer record. When fetching Orders for a customer, I'd also like to fetch Orders from slave Customers (ie the ones that claim the Customer I'm querying from is their master Customer record).

So:

Customer1: id: 1, master_id: nil, orders: [Order1, Order2]

Customer2: id: 2, master_id: 1, orders: [Order3]

query Customer1.all_orders should return all 3 Order objects

I know how to do this through a method - pluck ids of slave Customers, add the original customer's id to the array and then look for Orders whose customer_id is in this array:

has_many :slave_records, class_name: 'Customer', foreign_key: 'master_id'

def all_orders
  order_ids = slave_records.map(&:id).push(id)
  Order.where(customer_id: order_ids)
end

But is there a way to do this using scopes and relations? It's Rails 4 (I know that Rails 5 was supposed to have an OR thing in its version of ActiveRecord).

Answer 1

Adding scope in Order model will get you closer to what you want.

class Order
  scope :for_master, -> (master) { where("customer_id = #{master.id} OR customer_id IN (?)", master.slave_records.select(:id)) }
end

So for any master customer, call the scope and you will get orders for children too.

Order.for_master(customer)

You will not be able to call customer.all_orders . But, you will be able to get all results in a cleaner way.