sti_nested.rb

class Animal < ApplicationRecord
  belongs_to :place, polymorphic: true
end

class Monkey < Animal
  validates :name, presence: true
end

class Cat < Animal
  validates :breed, presence: true
end

class Jungle < ApplicationRecord
  has_many :animals, as: :place
  accepts_nested_attributes_of :animals, 
end

=> jungle = Jungle.new(animals_attributes: [{ type: 'Monkey', name: nil}, { type: 'Cat', beed: nil }])
=> jungle.valid?
=> false
=> jungle.errors.full_messages
=> ["Animals name can't be blank", "Animals breed can't be blank"]