belongs_to through associations

Delegate:

class Company < ActiveRecord::Base
  has_many :employees
  has_many :dogs, :through => :employees
end
 
class Employee < ActiveRescord::Base
  belongs_to :company
  has_many :dogs
end
 
class Dog < ActiveRecord::Base
  belongs_to :employee
 
  delegate :company, :to => :employee, :allow_nil => true
end

Use has_one instead of belongs_to in your :though  validates_uniqueness_of instead of using a proper unique constraint in your database:

class Choice
  belongs_to :user
  belongs_to :answer
  has_one :question, :through => :answer
end

   A belongs_to association cannot have a :through option off caching the question_id on Choice and adding a unique index to the table especially because validates_uniqueness_of is prone to race conditions.Add a custom validation to Choice that confirms that question_id matches,