Rails how to find an object through its polymorphic relationship?

Question

MongoDB

The database is mongodb, we use mongoid
The situation is as follows: The class country (Country)
Has many names through a polymorphic relationship:
(The reason is that you can find what it is by any name - is it a country?, a city? or a person? )
has_many :alternames, :as => :alternameable, :class_name => 'Altername'
class Altername
include Mongoid::Document
field :name, type: String
field :lang, type: String
belongs_to :alternameable, :polymorphic => true
end
I can not find a solution - how to get a Country by "name" - name (if, in principle, there is a Country with such a name)
Country.alternames.find_by(name: 'Vasya') doesn't work - says that unknown parameter alternames for Country:class

Answer 1

In general, I poorly understood the task, more precisely, how you solve it, but this of
course will not work, because has_many and all other possible connections have an instance of the class, and not the class.
That is, something like this should work for you.
Most likely, you need something like here:
Or variations (for example, add join, remove the name class, etc., already by context)
UPD :
I would in your case did concern

# app/models/concerns/alternameable.rb
module Alternameable

  extend ActiveSupport::Concern

  def self.included(base)

    base.class_eval do

      def has_altername_for?(name)
        joins(:alternames).where(name: name, alternameable_type: self.name).present?
      end

    end
  end

  module ClassMethods
  end

end

And connected to each class

class Country
include Alternameable
end