class Place < ApplicationRecord
end

class SubPlace < Place
    has_many :posts, class_name: "SubPlace", foreign_key: "sub_place_id"
end

class Post < ApplicationRecord
    belongs_to :sub_place, class_name: "SubPlace", foreign_key: "sub_place_id"
end

ActiveRecord::StatementInvalid (PG::UndefinedColumn: ERROR:  column places.sub_place_id does not exist)