[ActiveRecord] Get a polymorphic owner class out of the owned object

The question is: how can we retrieve a owners class of a polymorphic association without loading the owner object into memory?

class Source < ApplicationRecord
  self.has_one :state,
    dependent: :delete,
    as: :stateable
end

class State < ApplicationRecord
  belongs_to :stateable,
    polymorphic: true
end

Solution

There are (at least) two ways to do this. First one is not recommended (as it might fail with multiple namespaces with same class names, etc:

State.last.stateable_type.constantize #=> Source

or a better one that will work out of any scope:

State.last.association(:stateable).klass #=> Source