Question

Is there a way to find all Polymorphic models of a specific polymorphic type in Rails? So if I have Group, Event, and Project all with a declaration like:

has_many :assignments, :as => :assignable

Can I do something like:

Assignable.all

…or

BuiltInRailsPolymorphicHelper.all("assignable")

That would be nice.

Edit:

… such that Assignable.all returns [Event, Group, Product] (array of classes)

Answer 1

There is no direct method for this. I wrote this monkey patch for ActiveRecord::Base.
This will work for any class.

class ActiveRecord::Base

  def self.all_polymorphic_types(name)
    @poly_hash ||= {}.tap do |hash|
      Dir.glob(File.join(Rails.root, "app", "models", "**", "*.rb")).each do |file|
        klass = File.basename(file, ".rb").camelize.constantize rescue nil
        next unless klass.ancestors.include?(ActiveRecord::Base)

        klass.
          reflect_on_all_associations(:has_many).
          select{ |r| r.options[:as] }.
          each do |reflection|
            (hash[reflection.options[:as]] ||= []) << klass
          end
      end
    end
    @poly_hash[name.to_sym]
  end

end

Now you can do the following:

Assignable.all_polymorphic_types(:assignable).map(&:to_s)
# returns ['Project', 'Event', 'Group']