Ruby on Rails Creating a polymorphic join table

Found this via example here: https://stackoverflow.com/a/51564821/38375

Needed it to setup polymorphic join table for Product and ProductSubscription the join to the “Foo” table.

To set this up in Rails, I needed to do this:

class ProductsFoos < ApplicationRecord
  belongs_to :item, polymorphic: true
  belongs_to :foo
end

class Foo < ApplicationRecord
  has_many :products_foos, class_name: 'ProductsFoos', dependent: :destroy
  has_many :products, through: :products_foos
  has_many :product_subscriptions, through: :products_foos
end

class Product < ApplicationRecord
  has_many :products_foos, class_name: 'ProductsFoos', dependent: :destroy, as: :item
  has_many :foos, through: :products_foos
end

class ProductSubscription < ApplicationRecord
  has_many :products_foos, class_name: 'ProductsFoos', dependent: :destroy, as: :item
  has_many :foos, through: :products_foos
end

It was important to set belongs_to :item, polymorphic: true in the join-table class Then setup the has_many :products_foos and add as: :item

That then allows me to do this:

product = Product.last
product.foos << Foo.first

That creates a new join-table record, and sets item_id to product.id and item_type to "Product"