Rails : belongs_to and has_many using non-standard ids

Question

I've got two models, Item and Product as follows:

irb(main):007:0> Item
=> Item(id: integer, identification_number: string, production_date: date, 
        created_at: datetime, updated_at: datetime, going_in: boolean)
irb(main):008:0> Product
=> Product(id: integer, sku: string, barcode_identification: string, 
           created_at: datetime, updated_at: datetime)

Think of this as an item is of a particular product.

I've managed to refer all the items of a particular product (Product.find(1).items) via

class Product < ActiveRecord::Base
  has_many :items, :foreign_key => "identification_number", 
                   :primary_key => "barcode_identification"
end

but I can't seem to refer the Product of a particular item. This is what I've got now:

class Item < ActiveRecord::Base
  set_primary_key :identification_number
  belongs_to :product, :foreign_key => "barcode_identification"
end

And as far as my understanding re: databases are concerned, that should work. Except that it doesn't. Maybe I'm missing out on something here? I'm fairly new to rails (around a month or less.)

Answer 1

Does it have to be a belongs_to? Since you're specifying both primary and foreign key, why not

class Product < ActiveRecord::Base
  has_many :items, :foreign_key => "identification_number", 
                   :primary_key => "barcode_identification"
end

class Item < ActiveRecord::Base
  has_one :product, :foreign_key => "barcode_identification", 
                    :primary_key => "identification_number"
end