STI with many types - ruby-on-rails

Question

I have a rails 4 app with STI models:
# models/person.rb
def Person < ActiveRecord::Base
end
# models/director.rb
def Director < Person
end
# models/actor.rb
def Director < Person
end
But because one person can be an actor and an director simultaneously, I want STI with many types like:
person = Person.first
person.type = "Director, Actor"
person.save
Actor.first.id => 1
Director.first.id => 1
Is there mechanism in rails or gem for realize this?

Answer 1

Rails does not support this and I'm not aware of any gems that support this as described (i.e. multiple subclass names in the type column).
There is gem at https://github.com/mhuggins/multiple_table_inheritance which uses separate tables for the subclasses and you can always use mixins as an alternative to inheritance.

Answer 2

I believe the more Rails idiomatic way to do something similar would be via scopes, which would allow you to do:
person = Person.first
person.position = 'Director, Actor'
person.save
person.directors.first.id => 1
person.actors.first.id => 1
And you would just have to define a pair of scopes in your Person class:
scope :actors, -> { where('position like ?', '%Actor%') }
scope :directors, -> { where('position like ?', '%Director%') }
You would lose the ability to do person.is_a? with this, but Ruby doesn't really do multiple inheritance in such a way as to allow #is_a? to return true when passed sibling classes anyway. You can also get effectively similar functionality with a simple test method:
def is_actor?
self.position =~ /Actor/
end
def is_director?
self.position =~ /Director/
end
EDIT: I haven't done a lot of Rails 4, so my scope syntax MAY not be right, I just glanced at the docs. The principle should be sound, though.

Answer 3

Thank to all answerers above!
I found solution that most appropriate for me:
I've created hmt association Person-ProfessionsPerson-Profession and leave descendants for Person class (Director and Actor).
# models/profession.rb
Profession < ActiveRecord::Base
has_many :professions_people, dependent: :destroy
has_many :people, through: :professions_people
end
# models/person.rb
def Person < ActiveRecord::Base
has_many :professions_people, dependent: :destroy
has_many :professions, through: :professions_people
end
# models/director.rb
def Director < Person
include PeopleFromProfession
end
# models/actor.rb
def Actor < Person
include PeopleFromProfession
end
I've seed 2 professions with column "class_type" (which should not change in app's work) "Actor" and "Director"
I've also add concern PeopleFromProfession for share some code:
# models/concerns/actor.rb
module PeopleFromProfession
extend ActiveSupport::Concern
included do
default_scope { includes(:professions).where(professions: {class_type: self.name}) }
after_create :create_join_table_record
end
module ClassMethods
def model_name
Person.model_name
end
end
private
def create_join_table_record
self.professions << Profession.where(class_type: self.class.name).first
end
end
default_scope is for scoping only people with specific profession, create_join_table_record callback is monkey-patch for create missed join table record.
Class method model_name was overwriting for purposes, that covered here Best practices to handle routes for STI subclasses in rails
If you will find some problems in that approach, please tell me.