require 'active_record'

::ActiveRecord::Associations::Builder::HasOne.class_eval do
  # Based on
  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations/builder/collection_association.rb#L50
  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations/builder/singular_association.rb#L11
  def self.define_accessors(mixin, reflection)
    super
    name = reflection.name
    mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
      def #{name.to_s}_id
        association(:#{name}).reader.id
      end
    CODE
  end
end