Creating two different objects (from different models) at the same time - Rails

Question

I have two models: Product and Category, which I want to tie together. Say each product has a unique category, how do I set Rails to create (or generate) a new Category object each time a user creates a new Product object?

Answer 1

    class Product < ActiveRecord::Base
      after_create do
        Category.create product: self
      end
        has_one :category
    end

    class Category < ActiveRecord::Base
      belongs_to :product
    end

and in console

 > a= Product.create
 > a.category
 => #<Category id: 1, product_id: 5, created_at: "2015-11-04 12:53:22", updated_at: "2015-11-04 12:53:22">