file.rb

class Listing < ApplicationRecord
  belongs_to :author, class_name: 'Person', inverse_of: :listings
end

class Person < ApplicationRecord
  has_many :listings, foreign_key: 'author_id', inverse_of: :author
end

[4] pry(main)> Person.find('c-m9PWhIar54aabagq7ICb').listings.first.author;
  Person Load (0.9ms)  SELECT  `people`.* FROM `people` WHERE `people`.`id` = '1' LIMIT 1 
  Listing Load (0.5ms)  SELECT  `listings`.* FROM `listings` WHERE `listings`.`author_id` = '1' ORDER BY `listings`.`id` ASC LIMIT 1 
  Person Load (1.1ms)  SELECT  `people`.* FROM `people` WHERE `people`.`id` = '1' LIMIT 1