Using multiple has_many associations on one model

Question

I am working in a rails app where a Company has_many orders. An order has a name and that is it. The order can have_many television_spots, radio_placements, and newspaper_placements, the data in these tables is not the same so they have to be split up. Now if an order has_many radio_placements it will not have television_spots or newspaper_placements. My question is it bad practice to have a has_many relationship on a model even if it does not exist?, would it be better better to make a Company have_many television_orders and a television_order have_many television_spots? And thus a Company have_many radio_orders and a radio_order have_many radio_placements, and so on. I think that the first option is dryer initially but using the second strategy could result in cleaner more understandable code as the app grows and what we do with the data changes.

Answer 1

It's not bad practice to have a has_many association that does not actually have any models associated. The real question is what object type the radio_placements, television_spots and newspaper_placements should really be associated to. If they should in fact be related to the Order model, then place the associations there. From my understanding of your question/data shape it would appear that you do want these relationships to be on the Order model. So something like:

class Company
    has_many :orders
    has_many :television_spots, through: :orders
    has_many :radio_placements, through: :orders
    has_many :newspaper_placements, through: :orders
end

class Order
    has_many :television_spots
    has_many :radio_placements
    has_many :newspaper_placements
end

Hopefully that helps.